Write doubles with the shortest digits (Żmij), digits in registers

Write doubles with the conversion of Zmij by Victor Zverovich (MIT), ported to C++11 (detail/conversions/zmij.hpp). It finds the shortest decimal that reads back as the same double, and the closest one if there are several. Grisu2, used until now, is fast but not always shortest: it sometimes writes a 17th digit where 16 suffice, or a last digit that is not the closest. The layout is unchanged (1.5, 100.0, 1e+100, -0.0); float keeps Grisu2. Digits are converted eight at a time with the BCD conversion of Xiang JunBo, as in Zmij, and written with one byte swap per eight digits and fixed-size moves instead of per-digit loops. Leading and trailing zeros are counted from those bytes. to_chars() uses a local buffer when the caller's is shorter than the 41 bytes this may write. The powers of ten come from the number-parsing table, adjusted where it holds values rounded up, and extended with Zmij's compressed tables beyond 10^308. write_shortest() converts its 16 digits in one vector register (SSE2 on x86-64, NEON on 64-bit Arm, both baseline) and inserts the decimal point inside the register, avoiding a store-forwarding stall that cost about 25% of the time to write a double. dump() writes floats and integers straight into the serializer's write buffer instead of copying them from a member buffer, and small integers eight digits at a time. read_eight_bytes() and parse_eight_digits() are marked always-inline, which GCC had been calling out of line in the number-parsing loops. Of one million random doubles, about 0.14% are now written with different digits, always to a value that still reads back as the same double. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Speed up the lexer: own float parser, string scan, and \u table
2026-11-03 13:28:32 +00:00 · 2026-10-06 10:48:06 +02:00 · 2026-10-06 10:48:06 +02:00 · 2026-10-06 08:36:40 +02:00 · 2026-10-06 07:46:24 +02:00 · 2026-10-06 07:40:39 +02:00
88 changed files with 16292 additions and 1794 deletions
@@ -16,6 +16,9 @@ only_commits:

 environment:
  matrix:
+    # The Visual Studio 2017 jobs compile everything with /std:c++17, so they
+    # only build the C++17 variant of each test, split into two jobs each to
+    # stay below AppVeyor's 60-minute limit per job.
    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
      configuration: Debug
      platform: x86
@@ -34,7 +37,13 @@ environment:
      configuration: Release
      platform: x86
      CXX_FLAGS: "/permissive- /std:c++17 /utf-8 /W4 /WX"
-      CMAKE_OPTIONS: ""
+      CMAKE_OPTIONS: "-DJSON_TestStandards=17 -DJSON_TestShard=0/2"
+      GENERATOR: Visual Studio 15 2017
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
+      configuration: Release
+      platform: x86
+      CXX_FLAGS: "/permissive- /std:c++17 /utf-8 /W4 /WX"
+      CMAKE_OPTIONS: "-DJSON_TestStandards=17 -DJSON_TestShard=1/2"
      GENERATOR: Visual Studio 15 2017

    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
@@ -55,7 +64,13 @@ environment:
      configuration: Release
      platform: x64
      CXX_FLAGS: "/permissive- /std:c++17 /Zc:__cplusplus /utf-8 /W4 /WX"
-      CMAKE_OPTIONS: ""
+      CMAKE_OPTIONS: "-DJSON_TestStandards=17 -DJSON_TestShard=0/2"
+      GENERATOR: Visual Studio 15 2017
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
+      configuration: Release
+      platform: x64
+      CXX_FLAGS: "/permissive- /std:c++17 /Zc:__cplusplus /utf-8 /W4 /WX"
+      CMAKE_OPTIONS: "-DJSON_TestStandards=17 -DJSON_TestShard=1/2"
      GENERATOR: Visual Studio 15 2017

 init:
@@ -66,7 +81,7 @@ install:
  - if "%platform%"=="x86"    set GENERATOR_PLATFORM=Win32

 before_build:
-  - cmake . -G "%GENERATOR%" -A "%GENERATOR_PLATFORM%" -DCMAKE_CXX_FLAGS="%CXX_FLAGS%" -DCMAKE_IGNORE_PATH="C:/Program Files/Git/usr/bin" -DJSON_BuildTests=On "%CMAKE_OPTIONS%"
+  - cmake . -G "%GENERATOR%" -A "%GENERATOR_PLATFORM%" -DCMAKE_CXX_FLAGS="%CXX_FLAGS%" -DCMAKE_IGNORE_PATH="C:/Program Files/Git/usr/bin" -DJSON_BuildTests=On %CMAKE_OPTIONS%

 build_script:
  - cmake --build . --config "%configuration%" --parallel 2
@@ -17,11 +17,11 @@ permissions:
  contents: read

 jobs:
-  macos-14:
-    runs-on: macos-14 # https://github.com/actions/runner-images/blob/main/images/macos/macos-14-Readme.md
+  macos-15:
+    runs-on: macos-15 # https://github.com/actions/runner-images/blob/main/images/macos/macos-15-Readme.md
    strategy:
      matrix:
-        xcode: ['15.0.1', '15.1', '15.2', '15.3', '15.4']
+        xcode: ['16.0', '16.1', '16.2', '16.3', '16.4', '26.0.1', '26.1.1', '26.2', '26.3']
    env:
      DEVELOPER_DIR: /Applications/Xcode_${{ matrix.xcode }}.app/Contents/Developer

@@ -36,11 +36,11 @@ jobs:
      - name: Test
        run: cd build ; ctest -j 10 --output-on-failure

-  macos-15:
-    runs-on: macos-15 # https://github.com/actions/runner-images/blob/main/images/macos/macos-15-Readme.md
+  macos-26:
+    runs-on: macos-26 # https://github.com/actions/runner-images/blob/main/images/macos/macos-26-arm64-Readme.md
    strategy:
      matrix:
-        xcode: ['16.0', '16.1', '16.2', '16.3', '16.4', '26.0.1']
+        xcode: ['26.4.1', '26.5', '26.6']
    env:
      DEVELOPER_DIR: /Applications/Xcode_${{ matrix.xcode }}.app/Contents/Developer

@@ -107,7 +107,7 @@ jobs:
    container: ubuntu:24.04
    strategy:
      matrix:
-        target: [ci_cmake_flags, ci_test_diagnostics, ci_test_diagnostic_positions, ci_test_noexceptions, ci_test_noimplicitconversions, ci_test_legacycomparison, ci_test_noglobaludls, ci_test_disableenumserialization, ci_test_disabletuplereferenceconversion, ci_test_skiplibraryversioncheck, ci_test_simdutf, ci_test_strict_nul_handling, ci_test_no_thread_local]
+        target: [ci_cmake_flags, ci_test_diagnostics, ci_test_diagnostic_positions, ci_test_noexceptions, ci_test_noimplicitconversions, ci_test_legacycomparison, ci_test_noglobaludls, ci_test_disableenumserialization, ci_test_disabletuplereferenceconversion, ci_test_skiplibraryversioncheck, ci_test_simdutf, ci_test_strict_nul_handling, ci_test_delete_deprecated_functions, ci_test_no_thread_local]
    steps:
      - name: Install build-essential
        run: apt-get update ; apt-get install -y build-essential unzip wget git
@@ -209,7 +209,7 @@ jobs:
    strategy:
      matrix:
        # older GCC docker images (4, 5, 6) fail to check out code
-        compiler: ['7', '8', '9', '10', '11', '12', '13', '14', '15', 'latest']
+        compiler: ['7', '8', '9', '10', '11', '12', '13', '14', '15', '16', 'latest']
    container: gcc:${{ matrix.compiler }}
    steps:
      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
@@ -25,6 +25,7 @@ cc_library(
        "include/nlohmann/detail/conversions/from_json.hpp",
        "include/nlohmann/detail/conversions/to_chars.hpp",
        "include/nlohmann/detail/conversions/to_json.hpp",
+        "include/nlohmann/detail/conversions/zmij.hpp",
        "include/nlohmann/detail/exceptions.hpp",
        "include/nlohmann/detail/hash.hpp",
        "include/nlohmann/detail/input/binary_reader.hpp",
@@ -62,6 +62,7 @@ option(JSON_MultipleHeaders                "Use non-amalgamated version of the l
 option(JSON_SystemInclude                  "Include as system headers (skip for clang-tidy)." OFF)
 option(JSON_StrictNulHandling              "Build with strict NUL-byte handling enabled." OFF)
 option(JSON_StrictBinaryUTF8               "Build with UTF-8 checks in the CBOR, UBJSON, BJData, and BSON writers enabled." OFF)
+option(JSON_DeleteDeprecatedFunctions      "Delete the deprecated functions instead of only deprecating them." OFF)

 if (JSON_CI)
    include(ci)
@@ -123,6 +124,10 @@ if (JSON_StrictBinaryUTF8)
    message(STATUS "Strict UTF-8 checks in binary writers enabled (JSON_STRICT_BINARY_UTF8=1)")
 endif()

+if (JSON_DeleteDeprecatedFunctions)
+    message(STATUS "Deprecated functions are deleted (JSON_DELETE_DEPRECATED_FUNCTIONS=1)")
+endif()
+
 if (JSON_Diagnostic_Positions)
    message(STATUS "Diagnostic positions enabled (JSON_DIAGNOSTIC_POSITIONS=1)")
 endif()
@@ -159,6 +164,7 @@ target_compile_definitions(
    $<$<BOOL:${JSON_LegacyDiscardedValueComparison}>:JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON=1>
    $<$<BOOL:${JSON_StrictNulHandling}>:JSON_STRICT_NUL_HANDLING=1>
    $<$<BOOL:${JSON_StrictBinaryUTF8}>:JSON_STRICT_BINARY_UTF8=1>
+    $<$<BOOL:${JSON_DeleteDeprecatedFunctions}>:JSON_DELETE_DEPRECATED_FUNCTIONS=1>
 )

 target_include_directories(
@@ -1391,9 +1391,10 @@ THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR I

 - The class contains the UTF-8 Decoder from Bjoern Hoehrmann which is licensed under the [MIT License](https://opensource.org/licenses/MIT) (see above). Copyright &copy; 2008-2009 [Björn Hoehrmann](https://bjoern.hoehrmann.de/) <bjoern@hoehrmann.de>
 - The class contains a slightly modified version of the Grisu2 algorithm from Florian Loitsch which is licensed under the [MIT License](https://opensource.org/licenses/MIT) (see above). Copyright &copy; 2009 [Florian Loitsch](https://florian.loitsch.com/)
+- The class contains a port of the shortest double-to-decimal conversion of [Żmij](https://github.com/vitaut/zmij) by Victor Zverovich, which is licensed under the [MIT License](https://opensource.org/licenses/MIT) (see above). Copyright &copy; 2025 [Victor Zverovich](https://github.com/vitaut)
 - The class contains a copy of [Hedley](https://nemequ.github.io/hedley/) from Evan Nemerson which is licensed as [CC0-1.0](https://creativecommons.org/publicdomain/zero/1.0/).
 - The class contains parts of [Google Abseil](https://github.com/abseil/abseil-cpp) which is licensed under the [Apache 2.0 License](https://opensource.org/licenses/Apache-2.0).
- The class contains an adapted version of the Eisel-Lemire algorithm and its table of powers of five from [fast_float](https://github.com/fastfloat/fast_float) by Daniel Lemire and contributors, which is available under the [MIT License](https://opensource.org/licenses/MIT) (used here), the Apache 2.0 License, and the Boost Software License. Copyright &copy; 2021 The fast_float authors
+- The class contains an adapted version of the Eisel-Lemire algorithm, its table of powers of five, and its digit comparison for long numbers from [fast_float](https://github.com/fastfloat/fast_float) by Daniel Lemire and contributors, which is available under the [MIT License](https://opensource.org/licenses/MIT) (used here), the Apache 2.0 License, and the Boost Software License. Copyright &copy; 2021 The fast_float authors

 <img align="right" src="https://git.fsfe.org/reuse/reuse-ci/raw/branch/master/reuse-horizontal.png" alt="REUSE Software">

@@ -249,6 +249,20 @@ add_custom_target(ci_test_strict_nul_handling
    COMMENT "Compile and test with strict NUL-byte handling enabled"
 )

+###############################################################################
+# Delete the deprecated functions.
+###############################################################################
+
+add_custom_target(ci_test_delete_deprecated_functions
+    COMMAND ${CMAKE_COMMAND}
+    -DCMAKE_BUILD_TYPE=Debug -GNinja
+    -DJSON_BuildTests=ON -DJSON_FastTests=ON -DJSON_DeleteDeprecatedFunctions=ON
+    -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_delete_deprecated_functions
+    COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_delete_deprecated_functions
+    COMMAND cd ${PROJECT_BINARY_DIR}/build_delete_deprecated_functions && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
+    COMMENT "Compile and test with the deprecated functions deleted"
+)
+
 ###############################################################################
 # Disable global UDLs.
 ###############################################################################
@@ -362,7 +376,7 @@ add_custom_target(ci_test_coverage
 # Sanitizers.
 ###############################################################################

-set(CLANG_CXX_FLAGS_SANITIZER "-g -O1 -fsanitize=address -fsanitize=undefined -fsanitize=integer -fsanitize=nullability -fno-omit-frame-pointer -fno-sanitize-recover=all -fno-sanitize=unsigned-integer-overflow -fno-sanitize=unsigned-shift-base")
+set(CLANG_CXX_FLAGS_SANITIZER "-g -O1 -fsanitize=address -fsanitize=undefined -fsanitize=integer -fsanitize=nullability -fno-omit-frame-pointer -fno-sanitize-recover=all -fno-sanitize=unsigned-integer-overflow -fno-sanitize=unsigned-shift-base -fsanitize-ignorelist=${PROJECT_SOURCE_DIR}/cmake/clang_sanitizer_ignorelist.txt")

 add_custom_target(ci_test_clang_sanitizer
    COMMAND CXX=${CLANG_TOOL} CXXFLAGS=${CLANG_CXX_FLAGS_SANITIZER} ${CMAKE_COMMAND}
@@ -705,7 +719,7 @@ ci_get_cmake(4.0.0  CMAKE_4_0_0_BINARY)
 # the tests require CMake 3.13 or later, so they are excluded for CMake 3.5.0
 set(JSON_CMAKE_FLAGS_3_5_0 JSON_Diagnostics JSON_Diagnostic_Positions JSON_GlobalUDLs JSON_ImplicitConversions JSON_DisableEnumSerialization
    JSON_LegacyDiscardedValueComparison JSON_Install JSON_MultipleHeaders JSON_SystemInclude JSON_Valgrind
-    JSON_StrictNulHandling JSON_StrictBinaryUTF8)
+    JSON_StrictNulHandling JSON_StrictBinaryUTF8 JSON_DeleteDeprecatedFunctions)
 set(JSON_CMAKE_FLAGS_3_31_6 JSON_BuildTests ${JSON_CMAKE_FLAGS_3_5_0})
 set(JSON_CMAKE_FLAGS_4_0_0 JSON_BuildTests ${JSON_CMAKE_FLAGS_3_5_0})

@@ -0,0 +1,8 @@
+# Sanitizer ignore list for ci_test_clang_sanitizer (-fsanitize-ignorelist).
+#
+# libstdc++ 14's <format> declares `_Scanner(basic_string_view<_CharT>, size_t __nargs = -1)`, so every std::format
+# call converts -1 to size_t, which -fsanitize=integer reports as implicit-integer-sign-change. This is
+# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119429, not a bug in this library. Only that check and only <format> are
+# excluded, so implicit sign changes in the library and the tests are still reported.
+[implicit-integer-sign-change]
+src:*/include/c++/*/format
@@ -219,6 +219,7 @@ INSERT INTO searchIndex(name, type, path) VALUES ('Supported Macros', 'Guide', '
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_ASSERT', 'Macro', 'api/macros/json_assert/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_BRACE_INIT_COPY_SEMANTICS', 'Macro', 'api/macros/json_brace_init_copy_semantics/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_CATCH_USER', 'Macro', 'api/macros/json_throw_user/index.html');
+INSERT INTO searchIndex(name, type, path) VALUES ('JSON_DELETE_DEPRECATED_FUNCTIONS', 'Macro', 'api/macros/json_delete_deprecated_functions/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_DIAGNOSTICS', 'Macro', 'api/macros/json_diagnostics/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_DIAGNOSTIC_POSITIONS', 'Macro', 'api/macros/json_diagnostic_positions/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_DISABLE_ENUM_SERIALIZATION', 'Macro', 'api/macros/json_disable_enum_serialization/index.html');
@@ -249,6 +250,7 @@ INSERT INTO searchIndex(name, type, path) VALUES ('JSON_TRY_USER', 'Macro', 'api
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_USE_GLOBAL_UDLS', 'Macro', 'api/macros/json_use_global_udls/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_USE_IMPLICIT_CONVERSIONS', 'Macro', 'api/macros/json_use_implicit_conversions/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON', 'Macro', 'api/macros/json_use_legacy_discarded_value_comparison/index.html');
+INSERT INTO searchIndex(name, type, path) VALUES ('JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS', 'Macro', 'api/macros/json_use_objects_for_enum_keyed_maps/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_USE_SIMDUTF', 'Macro', 'api/macros/json_use_simdutf/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('Macros', 'Macro', 'api/macros/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE', 'Macro', 'api/macros/nlohmann_define_derived_type/index.html');
@@ -8,7 +8,7 @@ static basic_json diff(const basic_json& source,
 Creates a [JSON Patch](http://jsonpatch.com) so that value `source` can be changed into the value `target` by calling
 [`patch`](patch.md) function.

-For two JSON values `source` and `target`, the following code yields always `#!cpp true`:
+For two JSON values `source` and `target`, the following code always yields `#!cpp true`:
 ```cpp
 source.patch(diff(source, target)) == target;
 ```
@@ -27,7 +27,7 @@ a JSON patch to convert the `source` to `target`

 ## Exception safety

-Strong guarantee: if an exception is thrown, there are no changes in the JSON value.
+Strong guarantee: `source` and `target` are never modified.

 ## Complexity

@@ -62,6 +62,9 @@ Linear.

 ## Notes

+Floating-point numbers are written with the fewest digits that read back as the same value (for `#!cpp double`; see
+[number handling](../../features/types/number_handling.md#number-serialization)).
+
 Binary values are serialized as an object containing two keys:

 - "bytes": an array of bytes as integers
@@ -97,3 +100,5 @@ Binary values are serialized as an object containing two keys:
 - Error handlers added in version 3.4.0.
 - Serialization of binary values added in version 3.8.0.
 - Error handler `keep` added in version 3.13.0.
+- Doubles are written with the shortest digits (Żmij instead of Grisu2) since version 3.13.0; about 0.1% of doubles are
+  written differently, most of them with fewer digits.
@@ -120,3 +120,12 @@ Linear in the size of the input.
 - Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
 - Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
 - Added `error_handler` parameter in version 3.13.0.
+
+!!! warning "Deprecation"
+
+    - Overload (2) replaces calls to `from_bjdata` with a pointer and a length as first two parameters, which has been
+      deprecated in version 3.13.0. This overload will be removed in version 4.0.0. Please replace all calls like
+      `#!cpp from_bjdata(ptr, len, ...);` with `#!cpp from_bjdata(ptr, ptr+len, ...);`.
+
+    You should be warned by your compiler with a `-Wdeprecated-declarations` warning if you are using a deprecated
+    function.
@@ -106,3 +106,12 @@ Linear in the size of the input.
 ## Version history

 - Added in version 3.13.0.
+
+!!! warning "Deprecation"
+
+    - Overload (2) replaces calls to `from_bon8` with a pointer and a length as first two parameters, which has been
+      deprecated in version 3.13.0. This overload will be removed in version 4.0.0. Please replace all calls like
+      `#!cpp from_bon8(ptr, len, ...);` with `#!cpp from_bon8(ptr, ptr+len, ...);`.
+
+    You should be warned by your compiler with a `-Wdeprecated-declarations` warning if you are using a deprecated
+    function.
@@ -23,9 +23,10 @@ type to use.
 ## Template parameters

 `NumberFloatType`
-:   the type to store floating-point numbers. Parsing and serialization are implemented in terms of
-    `#!cpp std::strtof`/`#!cpp std::strtod`/`#!cpp std::strtold` and `#!cpp std::snprintf`, so the type must be
-    `#!cpp float`, `#!cpp double`, or `#!cpp long double`. The
+:   the type to store floating-point numbers. The parser converts `#!cpp float`, `#!cpp double`, and a
+    `#!cpp long double` that is IEEE 754 binary64 itself and other `#!cpp long double` formats with
+    `#!cpp std::from_chars` or `#!cpp std::strtold`, and serialization falls back to `#!cpp std::snprintf`, so the
+    type must be `#!cpp float`, `#!cpp double`, or `#!cpp long double`. The
    [binary formats](../../features/binary_formats/index.md) additionally require `#!cpp float` or `#!cpp double`,
    because they have no encoding for `#!cpp long double`. See
    [Template Parameter Requirements](../../features/types/template_parameters.md#numberfloattype).
@@ -55,6 +56,10 @@ This implementation does exactly follow this approach, as it uses double precisi
 smaller than `-1.79769313486232e+308` and values greater than `1.79769313486232e+308` will be stored as NaN internally
 and be serialized to `null`.

+During deserialization (from JSON text or any of the binary formats), a finite number that does not fit into
+`number_float_t` is rejected with [`out_of_range.406`](../../home/exceptions.md#jsonexceptionout_of_range406), for
+example a double-precision number in a binary format when `number_float_t` is `#!cpp float`.
+
 ### Storage

 Floating-point number values are stored directly inside a `basic_json` type.
@@ -47,8 +47,9 @@ With the default values for `NumberIntegerType` (`std::int64_t`), the default va

 When the default type is used, the maximal integer number that can be stored is `9223372036854775807` (INT64_MAX) and
 the minimal integer number that can be stored is `-9223372036854775808` (INT64_MIN). Integer numbers that are out of
-range will yield over/underflow when used in a constructor. During deserialization, too large or small integer numbers
-will automatically be stored as [`number_unsigned_t`](number_unsigned_t.md) or [`number_float_t`](number_float_t.md).
+range will yield over/underflow when used in a constructor. During deserialization (from JSON text or any of the binary
+formats), too large or small integer numbers will automatically be stored as [`number_unsigned_t`](number_unsigned_t.md)
+or [`number_float_t`](number_float_t.md).

 [RFC 8259](https://tools.ietf.org/html/rfc8259) further states:
 > Note that when such software is used, numbers that are integers and are in the range [-2<sup>53</sup>+1, 2<sup>53</sup>-1] are
@@ -48,8 +48,9 @@ With the default values for `NumberUnsignedType` (`std::uint64_t`), the default

 When the default type is used, the maximal integer number that can be stored is `18446744073709551615` (UINT64_MAX) and
 the minimal integer number that can be stored is `0`. Integer numbers that are out of range will yield over/underflow
-when used in a constructor. During deserialization, too large or small integer numbers will automatically be stored
-as [`number_integer_t`](number_integer_t.md) or [`number_float_t`](number_float_t.md).
+when used in a constructor. During deserialization (from JSON text or any of the binary formats), too large or small
+integer numbers will automatically be stored as [`number_integer_t`](number_integer_t.md) or
+[`number_float_t`](number_float_t.md).

 [RFC 8259](https://tools.ietf.org/html/rfc8259) further states:
 > Note that when such software is used, numbers that are integers and are in the range [-2<sup>53</sup>+1, 2<sup>53</sup>-1] are
@@ -68,6 +68,8 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
 - Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key in `j` is
  not valid UTF-8 and `error_handler` is `strict` (the default only if
  [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled)
+- Throws [type_error.321](../../home/exceptions.md#jsonexceptiontype_error321) if `j` or a value nested in it is
+  discarded; example: `"cannot serialize discarded value to BJData"`

 ## Complexity

@@ -119,4 +121,6 @@ Linear in the size of the JSON value `j`.
 - BJData version parameter (for draft3 binary encoding) added in version 3.12.0.
 - Added `error_handler` parameter in version 3.13.0. Its default, `keep`, writes the bytes of a string or object key
  that is not valid UTF-8 unchanged, as before; `strict` (the default if
-  [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled) throws `type_error.316`.
+  [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled) throws `type_error.316`.
+- Throws `type_error.321` for a discarded value since version 3.13.0; previously, a discarded value nested in an
+  array or object was silently skipped, producing invalid BJData.
@@ -58,6 +58,9 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
 - Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key is
  not valid UTF-8 and `error_handler` is `strict` (the default only if
  [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled)
+- Throws [type_error.321](../../home/exceptions.md#jsonexceptiontype_error321) if a value nested in `j` is discarded
+  (the top-level value itself is covered by `type_error.317` above, since it must be an object); example:
+  `"cannot serialize discarded value to BSON"`

 ## Complexity

@@ -110,6 +113,8 @@ pass before anything is written.
 - Throws `out_of_range.412` and `out_of_range.415` since version 3.13.0.
 - Linear in the size of `j`, and no longer limited by the call stack for deeply nested values, since version 3.13.0.
 - `out_of_range.415` is now detected before anything is written, like the other exceptions above, since version 3.13.0.
+- Throws `type_error.321` for a discarded value nested in `j` since version 3.13.0; previously, it was silently
+  skipped, producing a document whose declared size did not match what was actually written.
 - Added `error_handler` parameter in version 3.13.0. Its default, `keep`, writes the bytes of a string or object key
  that is not valid UTF-8 unchanged, as before; `strict` (the default if
  [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled) throws `type_error.316` before anything
@@ -49,6 +49,8 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
 - Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key in `j` is
  not valid UTF-8 and `error_handler` is `strict` (the default only if
  [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled)
+- Throws [type_error.321](../../home/exceptions.md#jsonexceptiontype_error321) if `j` or a value nested in it is
+  discarded; example: `"cannot serialize discarded value to CBOR"`

 ## Complexity

@@ -86,3 +88,5 @@ Linear in the size of the JSON value `j`.
 - Added `error_handler` parameter in version 3.13.0. Its default, `keep`, writes the bytes of a string or object key
  that is not valid UTF-8 unchanged, as before; `strict` (the default if
  [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled) throws `type_error.316`.
+- Throws `type_error.321` for a discarded value since version 3.13.0; previously, a discarded value nested in an
+  array or object was silently skipped, producing invalid CBOR.
@@ -54,6 +54,8 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
  `"subtype 70000 is too large for the MessagePack ext type (max 255)"`
 - Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key in `j` is
  not valid UTF-8 and `error_handler` is `strict`
+- Throws [type_error.321](../../home/exceptions.md#jsonexceptiontype_error321) if `j` or a value nested in it is
+  discarded; example: `"cannot serialize discarded value to MessagePack"`

 ## Complexity

@@ -108,3 +110,5 @@ Linear in the size of the JSON value `j`.
 - Fixed in version 3.13.0 to serialize `number_integer_t`/`number_unsigned_t` pairs of different width correctly;
  before, integers could be serialized with the wrong value if `number_integer_t` was narrower than
  `number_unsigned_t`.
+- Throws `type_error.321` for a discarded value since version 3.13.0; previously, a discarded value nested in an
+  array or object was silently skipped, producing invalid MessagePack.
@@ -61,6 +61,8 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
 - Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key in `j` is
  not valid UTF-8 and `error_handler` is `strict` (the default only if
  [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled)
+- Throws [type_error.321](../../home/exceptions.md#jsonexceptiontype_error321) if `j` or a value nested in it is
+  discarded; example: `"cannot serialize discarded value to UBJSON"`

 ## Complexity

@@ -112,3 +114,5 @@ Linear in the size of the JSON value `j`.
 - Added `error_handler` parameter in version 3.13.0. Its default, `keep`, writes the bytes of a string or object key
  that is not valid UTF-8 unchanged, as before; `strict` (the default if
  [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled) throws `type_error.316`.
+- Throws `type_error.321` for a discarded value since version 3.13.0; previously, a discarded value nested in an
+  array or object was silently skipped, producing invalid UBJSON.
@@ -58,6 +58,13 @@ header. See also the [macro overview page](../../features/macros.md).
 - [**JSON_DISABLE_ENUM_SERIALIZATION**](json_disable_enum_serialization.md) - switch off default serialization/deserialization functions for enums
 - [**JSON_DISABLE_TUPLE_REFERENCE_CONVERSION**](json_disable_tuple_reference_conversion.md) - switch off conversion from a one-element tuple of a JSON reference
 - [**JSON_USE_IMPLICIT_CONVERSIONS**](json_use_implicit_conversions.md) - control implicit conversions
+- [**JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS**](json_use_objects_for_enum_keyed_maps.md) - opt in to storing maps with enum
+  keys as objects
+
+## Deprecated functions
+
+- [**JSON_DELETE_DEPRECATED_FUNCTIONS**](json_delete_deprecated_functions.md) - opt in to deleting the deprecated
+  functions ahead of their removal in version 4.0.0

 ## Comparison behavior

@@ -0,0 +1,96 @@
+# JSON_DELETE_DEPRECATED_FUNCTIONS
+
+```cpp
+#define JSON_DELETE_DEPRECATED_FUNCTIONS /* value */
+```
+
+When defined to `1`, all [deprecated functions](../../community/roadmap.md#removal-of-deprecated-functions) of the
+library are declared as deleted (`= delete`) instead of only being marked as deprecated. Code that still calls one of
+them no longer compiles. This way, you can find all calls that need to be replaced before version 4.0.0 removes these
+functions; the [migration guide](../../integration/migration_guide.md#replace-deprecated-functions) describes how.
+
+A deleted function, unlike a removed one, still takes part in overload resolution. A call that would select it
+therefore fails to compile instead of silently selecting another overload. This matters for the deprecated
+`from_*(ptr, len)` overloads of [`from_cbor`](../basic_json/from_cbor.md), [`from_msgpack`](../basic_json/from_msgpack.md),
+[`from_ubjson`](../basic_json/from_ubjson.md), [`from_bjdata`](../basic_json/from_bjdata.md),
+[`from_bon8`](../basic_json/from_bon8.md), and [`from_bson`](../basic_json/from_bson.md): without them, a call like
+`from_cbor(ptr, len)` would compile, read `ptr` as a NUL-terminated string, and convert `len` to the `strict` parameter.
+
+The macro does not affect the deprecated legacy comparison of discarded values, which is controlled by
+[`JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON`](json_use_legacy_discarded_value_comparison.md).
+
+## Default definition
+
+The default value is `0` (disabled, the deprecated functions can still be called, and the compiler warns about it).
+
+```cpp
+#define JSON_DELETE_DEPRECATED_FUNCTIONS 0
+```
+
+## Notes
+
+!!! info "CMake option"
+
+    The macro can also be set with the CMake option
+    [`JSON_DeleteDeprecatedFunctions`](../../integration/cmake.md#json_deletedeprecatedfunctions) (`OFF` by default).
+
+!!! warning "Opt-in only"
+
+    This macro must be defined **before** including `<nlohmann/json.hpp>`. Defining it after the include has no
+    effect. Define it for the whole project to avoid different declarations of the same class in different
+    translation units.
+
+!!! note "ABI compatibility"
+
+    The macro only turns calls that compile into calls that do not; it does not change the layout or the behavior of
+    any type. Its value is therefore not encoded in the [namespace](../../features/namespace.md).
+
+## Examples
+
+??? example "Example: default behavior (macro not defined)"
+
+    Without the macro, the deprecated overload is called, and the compiler warns about it:
+
+    ```cpp
+    #include <nlohmann/json.hpp>
+
+    using json = nlohmann::json;
+
+    int main()
+    {
+        const std::vector<std::uint8_t> v = {0x82, 0x01, 0x02};
+        auto j = json::from_cbor(v.data(), v.size());
+        // warning: 'from_cbor' is deprecated: Since 3.8.0; use from_cbor(ptr, ptr + len)
+    }
+    ```
+
+??? example "Example: deleted deprecated functions (macro defined to 1)"
+
+    With the macro, the call does not compile:
+
+    ```cpp
+    #define JSON_DELETE_DEPRECATED_FUNCTIONS 1
+    #include <nlohmann/json.hpp>
+
+    using json = nlohmann::json;
+
+    int main()
+    {
+        const std::vector<std::uint8_t> v = {0x82, 0x01, 0x02};
+        auto j = json::from_cbor(v.data(), v.size());
+        // error: call to deleted function 'from_cbor'
+    }
+    ```
+
+## See also
+
+- [Roadmap: removal of deprecated functions](../../community/roadmap.md#removal-of-deprecated-functions) - the
+  deprecated functions and the version they were deprecated in
+- [Migration guide: replace deprecated functions](../../integration/migration_guide.md#replace-deprecated-functions) -
+  how to replace each deprecated function
+
+## Version history
+
+- Added in version 3.13.0.
+- Planned to be removed in version 4.0.0, which removes the deprecated functions. The deprecated `from_*(ptr, len)`
+  overloads stay deleted in version 4.0.0.
@@ -112,3 +112,4 @@ The default value is `0` (disabled — existing behavior is preserved).
 ## Version history

 - Added in version 3.13.0.
+- Planned to become the default (with the macro removed) in version 4.0.0.
@@ -44,7 +44,7 @@ By default, implicit conversions are enabled.

 ## Examples

-??? example "Example: implicit conversion"
+??? example "Example: implicit and explicit conversions"

    This is an example for an implicit conversion:

@@ -0,0 +1,139 @@
+# JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
+
+```cpp
+#define JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS /* value */
+```
+
+When defined to `1`, maps whose keys are enums (such as `std::map<E, T>` or `std::unordered_map<E, T>`) are stored as
+JSON objects, using the enum's own conversion for the keys. By default, they are stored as arrays of `[key, value]`
+pairs.
+
+## Default definition
+
+The default value is `0` (disabled — existing behavior is preserved).
+
+```cpp
+#define JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS 0
+```
+
+## Notes
+
+!!! note "Background"
+
+    JSON object keys are strings, so a map is only stored as an object if its keys can be converted to a string type.
+    Enums are not, even if [`NLOHMANN_JSON_SERIALIZE_ENUM`](nlohmann_json_serialize_enum.md) maps them to strings, so a
+    map with enum keys becomes an array of `[key, value]` pairs:
+
+    ```json
+    [["stopped", "aa"], ["completed", "bb"]]
+    ```
+
+    With this macro, the same map becomes an object
+    (see [#4378](https://github.com/nlohmann/json/issues/4378)):
+
+    ```json
+    {"completed": "bb", "stopped": "aa"}
+    ```
+
+!!! note "Maps with non-unique keys"
+
+    Maps that allow duplicate keys, such as `std::multimap<E, T>` or `std::unordered_multimap<E, T>`, are not affected
+    by the macro and are still stored as arrays of `[key, value]` pairs, as an object cannot hold duplicate keys.
+
+!!! note "Reading"
+
+    Reading is not affected by the macro: a map with enum keys can always be read from both an array of pairs and an
+    object. For the latter, each key is converted to the enum with its `from_json` function, e.g., the one defined by
+    [`NLOHMANN_JSON_SERIALIZE_ENUM`](nlohmann_json_serialize_enum.md). Data written without the macro can therefore
+    still be read after enabling it.
+
+!!! warning "Keys must serialize to distinct strings"
+
+    Each key is converted with the enum's `to_json` function. If a key is not converted to a string (for instance, an
+    enum without [`NLOHMANN_JSON_SERIALIZE_ENUM`](nlohmann_json_serialize_enum.md), which is stored as an integer, or an
+    enumerator mapped to `nullptr`), [`type_error.302`](../../home/exceptions.md#jsonexceptiontype_error302) is thrown.
+    If two keys are converted to the same string (for instance, because
+    [`NLOHMANN_JSON_SERIALIZE_ENUM`](nlohmann_json_serialize_enum.md) maps an unlisted enumerator to the first entry),
+    [`type_error.318`](../../home/exceptions.md#jsonexceptiontype_error318) is thrown. In both cases, the target value
+    is not changed.
+
+!!! warning "Opt-in only"
+
+    This macro must be defined **before** including `<nlohmann/json.hpp>`. Defining it after the include has no effect.
+
+!!! note "ABI compatibility"
+
+    The value of this macro is encoded in the [namespace](../../features/namespace.md) (tag `_ekmo`), resulting in
+    distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program
+    without One Definition Rule (ODR) violations, but they cannot exchange instances of library types.
+
+## Examples
+
+??? example "Example: default behavior (macro not defined)"
+
+    Without the macro, a map with enum keys is stored as an array of pairs:
+
+    ```cpp
+    #include <map>
+    #include <nlohmann/json.hpp>
+
+    using json = nlohmann::json;
+
+    enum TaskState { TS_STOPPED, TS_RUNNING, TS_COMPLETED };
+
+    NLOHMANN_JSON_SERIALIZE_ENUM(TaskState, {
+        {TS_STOPPED, "stopped"},
+        {TS_RUNNING, "running"},
+        {TS_COMPLETED, "completed"},
+    })
+
+    int main()
+    {
+        std::map<TaskState, std::string> m = {{TS_STOPPED, "aa"}, {TS_COMPLETED, "bb"}};
+
+        json j = m;
+        // j is [["stopped","aa"],["completed","bb"]]
+    }
+    ```
+
+??? example "Example: objects for enum-keyed maps (macro defined to 1)"
+
+    With the macro, the same map is stored as an object:
+
+    ```cpp
+    #define JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS 1
+    #include <map>
+    #include <nlohmann/json.hpp>
+
+    using json = nlohmann::json;
+
+    enum TaskState { TS_STOPPED, TS_RUNNING, TS_COMPLETED };
+
+    NLOHMANN_JSON_SERIALIZE_ENUM(TaskState, {
+        {TS_STOPPED, "stopped"},
+        {TS_RUNNING, "running"},
+        {TS_COMPLETED, "completed"},
+    })
+
+    int main()
+    {
+        std::map<TaskState, std::string> m = {{TS_STOPPED, "aa"}, {TS_COMPLETED, "bb"}};
+
+        json j = m;
+        // j is {"completed":"bb","stopped":"aa"}
+
+        auto m2 = j.get<std::map<TaskState, std::string>>();
+        // m2 == m
+    }
+    ```
+
+## See also
+
+- [Specializing enum conversion](../../features/enum_conversion.md)
+- [**NLOHMANN_JSON_SERIALIZE_ENUM**](nlohmann_json_serialize_enum.md) - serialize/deserialize an enum
+- [**NLOHMANN_JSON_SERIALIZE_ENUM_STRICT**](nlohmann_json_serialize_enum_strict.md) - serialize/deserialize an enum with
+  exceptions
+
+## Version history
+
+- Added in version 3.13.0.
@@ -41,6 +41,9 @@ inline void from_json(const BasicJsonType& j, type& e);
      conversion. Select this default pair carefully. See example 1 below.
    - If an enum or JSON value is specified in multiple conversions, the first matching conversion from the top of the
      list will be returned when converting to or from JSON. See example 2 below.
+    - Maps with enum keys (e.g., `std::map<ENUM_TYPE, T>`) are stored as arrays of `[key, value]` pairs by default.
+      Define [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](json_use_objects_for_enum_keyed_maps.md) to store them as objects
+      with the converted keys. Such maps can be read from both forms.

 ## Examples

@@ -80,6 +83,7 @@ inline void from_json(const BasicJsonType& j, type& e);
 - [Specializing enum conversion](../../features/enum_conversion.md)
 - [`NLOHMANN_JSON_SERIALIZE_ENUM_STRICT`](./nlohmann_json_serialize_enum_strict.md)
 - [`JSON_DISABLE_ENUM_SERIALIZATION`](json_disable_enum_serialization.md)
+- [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](json_use_objects_for_enum_keyed_maps.md)

 ## Version history

@@ -44,6 +44,9 @@ inline void from_json(const BasicJsonType& j, type& e);
      `"enum value out of range for <type>"`.
    - If an enum or JSON value is specified in multiple conversions, the first matching conversion from the top of the
      list will be returned when converting to or from JSON. See example 2 below.
+    - Maps with enum keys (e.g., `std::map<ENUM_TYPE, T>`) are stored as arrays of `[key, value]` pairs by default.
+      Define [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](json_use_objects_for_enum_keyed_maps.md) to store them as objects
+      with the converted keys. Such maps can be read from both forms.

 ## Examples

@@ -99,6 +102,7 @@ inline void from_json(const BasicJsonType& j, type& e);
 - [Specializing enum conversion](../../features/enum_conversion.md)
 - [`NLOHMANN_JSON_SERIALIZE_ENUM`](./nlohmann_json_serialize_enum.md)
 - [`JSON_DISABLE_ENUM_SERIALIZATION`](json_disable_enum_serialization.md)
+- [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](json_use_objects_for_enum_keyed_maps.md)

 ## Version history

@@ -21,17 +21,18 @@ Note: Some modern features (like C++20 ranges or filesystem support) may be disa
      
        | Compiler                                     | Architecture | Operating System                  | CI        |
        |----------------------------------------------|--------------|-----------------------------------|-----------|
-        | AppleClang 15.0.0.15000040; Xcode 15.0.1     | arm64        | macOS 14.7.2 (Sonoma)             | GitHub    |
-        | AppleClang 15.0.0.15000100; Xcode 15.1       | arm64        | macOS 14.7.2 (Sonoma)             | GitHub    |
-        | AppleClang 15.0.0.15000100; Xcode 15.2       | arm64        | macOS 14.7.2 (Sonoma)             | GitHub    |
-        | AppleClang 15.0.0.15000309; Xcode 15.3       | arm64        | macOS 14.7.2 (Sonoma)             | GitHub    |
-        | AppleClang 15.0.0.15000309; Xcode 15.4       | arm64        | macOS 14.7.2 (Sonoma)             | GitHub    |
        | AppleClang 16.0.0.16000026; Xcode 16         | arm64        | macOS 15.2 (Sequoia)              | GitHub    |
        | AppleClang 16.0.0.16000026; Xcode 16.1       | arm64        | macOS 15.2 (Sequoia)              | GitHub    |
        | AppleClang 16.0.0.16000026; Xcode 16.2       | arm64        | macOS 15.2 (Sequoia)              | GitHub    |
        | AppleClang 17.0.0.17000013; Xcode 16.3       | arm64        | macOS 15.5 (Sequoia)              | GitHub    |
        | AppleClang 17.0.0.17000013; Xcode 16.4       | arm64        | macOS 15.5 (Sequoia)              | GitHub    |
        | AppleClang 17.0.0.17000319; Xcode 26.0.1     | arm64        | macOS 15.5 (Sequoia)              | GitHub    |
+        | AppleClang 17.0.0.17000404; Xcode 26.1.1     | arm64        | macOS 15.7.9 (Sequoia)            | GitHub    |
+        | AppleClang 17.0.0.17000603; Xcode 26.2       | arm64        | macOS 15.7.9 (Sequoia)            | GitHub    |
+        | AppleClang 17.0.0.17000604; Xcode 26.3       | arm64        | macOS 15.7.9 (Sequoia)            | GitHub    |
+        | AppleClang 21.0.0.21000099; Xcode 26.4.1     | arm64        | macOS 26.6.2 (Tahoe)              | GitHub    |
+        | AppleClang 21.0.0.21000101; Xcode 26.5       | arm64        | macOS 26.6.2 (Tahoe)              | GitHub    |
+        | AppleClang 21.0.0.21000101; Xcode 26.6       | arm64        | macOS 26.6.2 (Tahoe)              | GitHub    |
        | Clang 3.4.2                                  | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
        | Clang 3.5.2                                  | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
        | Clang 3.6.2                                  | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
@@ -89,7 +90,7 @@ Note: Some modern features (like C++20 ranges or filesystem support) may be disa
        | GNU 13.3.0                                   | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
        | GNU 14.2.0                                   | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
        | GNU 15.1.0                                   | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
-        | GNU 16.1.0                                   | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
+        | GNU 16.2.0                                   | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
        | GNU 16.1.0                                   | arm64        | Ubuntu 24.04                      | GitHub    |
        | icpc (ICC) 2021.10.0 20230609                | x86_64       | Ubuntu 22.04 LTS                  | GitHub    |
        | icpx (Intel oneAPI DPC++/C++) 2025.3.2       | x86_64       | Ubuntu 24.04 LTS                  | GitHub    |
@@ -64,6 +64,8 @@ The following macros guard changes that are planned to become the default in ver
 | [`JSON_PRECISE_STREAM_POSITION`](../api/macros/json_precise_stream_position.md)                                  | `0`         | `1`: reading from a stream does not consume the character after a number                                                      | –                                                                                                                  | 3.13.0 |
 | [`JSON_STRICT_NUL_HANDLING`](../api/macros/json_strict_nul_handling.md)                                          | `0`         | `1`: a NUL byte in the input is a parse error instead of the end of input                                                     | [`JSON_StrictNulHandling`](../integration/cmake.md#json_strictnulhandling)                                         | 3.13.0 |
 | [`JSON_STRICT_BINARY_UTF8`](../api/macros/json_strict_binary_utf8.md)                                            | `0`         | `1`: `to_cbor`, `to_ubjson`, `to_bjdata`, and `to_bson` throw for strings that are not valid UTF-8 by default                 | [`JSON_StrictBinaryUTF8`](../integration/cmake.md#json_strictbinaryutf8)                                           | 3.13.0 |
+| [`JSON_DISABLE_TUPLE_REFERENCE_CONVERSION`](../api/macros/json_disable_tuple_reference_conversion.md)            | `0`         | `1`: a `basic_json` value can no longer be created from a one-element tuple of a reference to it, such as `std::forward_as_tuple(j)`| [`JSON_DisableTupleReferenceConversion`](../integration/cmake.md#json_disabletuplereferenceconversion)             | 3.13.0 |
+| [`JSON_DELETE_DEPRECATED_FUNCTIONS`](../api/macros/json_delete_deprecated_functions.md)                          | `0`         | removed: the deprecated functions are removed (see below); the `from_*(ptr, len)` overloads stay deleted                      | [`JSON_DeleteDeprecatedFunctions`](../integration/cmake.md#json_deletedeprecatedfunctions)                         | 3.13.0 |

 For example, the following makes a 3.x release behave like version 4.0 with respect to these changes:

@@ -75,6 +77,8 @@ For example, the following makes a 3.x release behave like version 4.0 with resp
 #define JSON_PRECISE_STREAM_POSITION 1
 #define JSON_STRICT_NUL_HANDLING 1
 #define JSON_STRICT_BINARY_UTF8 1
+#define JSON_DISABLE_TUPLE_REFERENCE_CONVERSION 1
+#define JSON_DELETE_DEPRECATED_FUNCTIONS 1
 #include <nlohmann/json.hpp>
 ```

@@ -84,8 +88,13 @@ way to achieve this.
 ### Removal of deprecated functions

 Version 4.0 will remove all deprecated functions. Compiling with deprecation warnings enabled shows which of them your
-code still uses. The [migration guide](../integration/migration_guide.md#replace-deprecated-functions) shows how to
-replace each of them.
+code still uses. Defining [`JSON_DELETE_DEPRECATED_FUNCTIONS`](../api/macros/json_delete_deprecated_functions.md) to
+`1` turns these warnings into errors, as the deprecated functions are then deleted. The
+[migration guide](../integration/migration_guide.md#replace-deprecated-functions) shows how to replace each of them.
+
+The `from_*` overloads taking a pointer and a length are not removed in version 4.0, but stay deleted. Without them, a
+call like `from_cbor(ptr, len)` would still compile: it would read `ptr` as a NUL-terminated string and convert `len`
+to the `strict` parameter.

 | Deprecated                                                                                                                                                                                                                                         | Since  | Migration                                                                        |
 |----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------|----------------------------------------------------------------------------------|
@@ -97,6 +106,7 @@ replace each of them.
 | [`json_pointer::operator string_t`](../api/json_pointer/operator_string_t.md)                                                                                                                                                                      | 3.11.0 | [JSON Pointers](../integration/migration_guide.md#json-pointers)                 |
 | [`json_pointer`](../api/json_pointer/index.md) with a `basic_json` type as template argument, and the overloads of `value`, `contains`, `operator[]`, and `at` accepting such a pointer                                                           | 3.11.0 | [JSON Pointers](../integration/migration_guide.md#json-pointers)                 |
 | Comparing a [`json_pointer`](../api/json_pointer/index.md) with a string via [`operator==`](../api/json_pointer/operator_eq.md) or [`operator!=`](../api/json_pointer/operator_ne.md)                                                              | 3.11.2 | [JSON Pointers](../integration/migration_guide.md#json-pointers)                 |
+| [`from_bjdata`](../api/basic_json/from_bjdata.md) and [`from_bon8`](../api/basic_json/from_bon8.md) with `(ptr, len)`                                                                                                                              | 3.13.0 | [Parsing](../integration/migration_guide.md#parsing)                             |

 The deprecated legacy comparison of discarded values is controlled by a macro and therefore listed in the table above.

@@ -168,9 +168,9 @@ The library maps CBOR types to JSON value types as follows:
 !!! warning "Negative integer overflow"

    CBOR negative integers (major type 1) are decoded as `-1 - n`. If the encoded magnitude `n` is too large for the
-    result to fit into `number_integer_t` (`std::int64_t` by default), parsing fails with a
-    [`parse_error.112`](../../home/exceptions.md#jsonexceptionparse_error112) exception rather than overflowing
-    silently.
+    result to fit into `number_integer_t` (`std::int64_t` by default), the result is stored as `number_float_t`, like
+    a too small integer in JSON text. For example, `-18446744073709551616` (`0x3B` followed by eight `0xFF` bytes) is
+    stored as `-1.8446744073709552e+19`.

 !!! warning "Object keys"

@@ -58,6 +58,23 @@ assert(jPi.get<TaskState>() == TS_INVALID );
    --8<-- "examples/nlohmann_json_serialize_enum.output"
    ```

+## Maps with enum keys
+
+By default, maps with enum keys, such as `std::map<TaskState, std::string>`, are stored as arrays of `[key, value]`
+pairs, because JSON object keys must be strings. Define
+[`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](../api/macros/json_use_objects_for_enum_keyed_maps.md) before including the
+library to store them as objects, with the keys converted by the enum's `to_json()` function:
+
+```cpp
+std::map<TaskState, std::string> m = {{TS_STOPPED, "aa"}, {TS_COMPLETED, "bb"}};
+
+json j = m;
+// default:                                   [["stopped","aa"],["completed","bb"]]
+// with JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS: {"completed":"bb","stopped":"aa"}
+```
+
+Either form can be read back, with or without the macro.
+
 ## Notes

 Just as in [Arbitrary Type Conversions](arbitrary_types.md) above,
@@ -23,6 +23,17 @@ This macro overrides [`#!cpp catch`](https://en.cppreference.com/w/cpp/language/

 See [full documentation of `JSON_CATCH_USER(exception)`](../api/macros/json_throw_user.md).

+## `JSON_DELETE_DEPRECATED_FUNCTIONS`
+
+When defined to `1`, all deprecated functions are declared as deleted instead of only being marked as deprecated, so
+code that still calls them no longer compiles. This way, you can find all calls that need to be replaced before version
+4.0.0 removes these functions.
+
+The macro can also be set with the CMake option
+[`JSON_DeleteDeprecatedFunctions`](../integration/cmake.md#json_deletedeprecatedfunctions) (`OFF` by default).
+
+See [full documentation of `JSON_DELETE_DEPRECATED_FUNCTIONS`](../api/macros/json_delete_deprecated_functions.md).
+
 ## `JSON_DIAGNOSTICS`

 This macro enables extended diagnostics for exception messages. Possible values are `1` to enable or `0` to disable
@@ -86,7 +97,8 @@ See [full documentation of `JSON_DISABLE_ENUM_SERIALIZATION`](../api/macros/json
 ## `JSON_DISABLE_TUPLE_REFERENCE_CONVERSION`

 When defined to `1`, a JSON value can no longer be created from a one-element `std::tuple` holding a reference to a JSON
-value, such as the result of `std::forward_as_tuple(j)`. This lets `std::tuple` convert such tuples element-wise.
+value, such as the result of `std::forward_as_tuple(j)`. This lets `std::tuple` convert such tuples element-wise. This
+is planned to become the default in version 4.0.0.

 See [full documentation of `JSON_DISABLE_TUPLE_REFERENCE_CONVERSION`](../api/macros/json_disable_tuple_reference_conversion.md).

@@ -198,6 +210,13 @@ default.

 See [full documentation of `JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON`](../api/macros/json_use_legacy_discarded_value_comparison.md).

+## `JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`
+
+When defined to `1`, maps with enum keys (e.g., `std::map<E, T>`) are stored as objects, using the enum's conversion for
+the keys, instead of arrays of `[key, value]` pairs. It is switched off (`0`) by default.
+
+See [full documentation of `JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](../api/macros/json_use_objects_for_enum_keyed_maps.md).
+
 ## `JSON_USE_SIMDUTF`

 When defined, UTF-8 validation of JSON strings read from contiguous byte input is delegated to the
@@ -21,6 +21,8 @@ The complete default namespace name is derived as follows:
    - [`JSON_PRECISE_STREAM_POSITION`](../api/macros/json_precise_stream_position.md) defined non-zero appends `_psp`.
    - [`JSON_STRICT_NUL_HANDLING`](../api/macros/json_strict_nul_handling.md) defined non-zero appends `_snul`.
    - [`JSON_STRICT_BINARY_UTF8`](../api/macros/json_strict_binary_utf8.md) defined non-zero appends `_sbu8`.
+    - [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](../api/macros/json_use_objects_for_enum_keyed_maps.md) defined non-zero
+      appends `_ekmo`.
 - The inline namespace ends with the suffix `_v` followed by the 3 components of the version number separated by
  underscores. To omit the version component, see [Disabling the version component](#disabling-the-version-component)
  below.
@@ -82,12 +82,13 @@ flowchart TD

    - Numbers with a decimal digit or scientific notation are always stored as `#!c double`.
    - The number types can be changed, see [Template number types](#template-number-types). 
-    - Integers are converted by the library's own digit parser. Floating-point numbers are converted with
-      [`std::from_chars`](https://en.cppreference.com/w/cpp/utility/from_chars) if the library is compiled with C++17
-      and the standard library supports it, then with an exact fast path for `#!c double` values with few significant
-      digits, and otherwise with the locale-aware
-      [`std::strtod`](https://en.cppreference.com/w/cpp/string/byte/strtof) (`std::strtof`/`std::strtold` for the
-      other floating-point types). Before version 3.13.0, the conversion was realized by
+    - The library converts integers and floating-point numbers itself, independent of the locale. Floating-point
+      numbers are correctly rounded (to nearest, ties to even). Only a `#!c long double` that is not IEEE 754 binary64
+      (e.g., the 80-bit x87 format) is converted with `#!cpp std::from_chars` where available, or else with
+      [`std::strtold`](https://en.cppreference.com/w/cpp/string/byte/strtof). For that call, the library temporarily
+      replaces the `.` with the decimal point of the current locale (which may be longer than one byte, e.g., in
+      `fa_IR.UTF-8`), so the result does not depend on the locale either. Changing the locale in another thread during
+      parsing is undefined behavior of the C library, though. Before version 3.13.0, the conversion was realized by
      [`std::strtoull`](https://en.cppreference.com/w/cpp/string/byte/strtoul),
      [`std::strtoll`](https://en.cppreference.com/w/cpp/string/byte/strtol), and `std::strtod`, respectively.

@@ -100,10 +101,10 @@ flowchart TD
 ### Number limits

 - Any 64-bit signed or unsigned integer can be stored without loss of precision.
- Numbers exceeding the limits of `#!c double` (i.e., numbers that after conversion via
-[`std::strtod`](https://en.cppreference.com/w/cpp/string/byte/strtof) are not satisfying
+- Numbers exceeding the limits of `#!c double` (i.e., numbers whose rounded value is not satisfying
 [`std::isfinite`](https://en.cppreference.com/w/cpp/numeric/math/isfinite) such as `#!c 1E400`) will throw exception
-[`json.exception.out_of_range.406`](../../home/exceptions.md#jsonexceptionout_of_range406) during parsing.
+[`json.exception.out_of_range.406`](../../home/exceptions.md#jsonexceptionout_of_range406) during parsing. Numbers too
+small for `#!c double` (such as `#!c 1E-400`) become zero, with the sign of the number.
 - Floating-point numbers are rounded to the next number representable as `double`. For instance
 `#!c 3.141592653589793238462643383279` is stored as [`0x400921fb54442d18`](https://float.exposed/0x400921fb54442d18).
 This is the same behavior as the code `#!c double x = 3.141592653589793238462643383279;`.
@@ -133,9 +134,10 @@ That is, `-0` is stored as a signed integer, but the serialization does not repr
 ### Number serialization

 - Integer numbers are serialized as is; that is, no scientific notation is used.
- Floating-point numbers are serialized as specified by the `#!c %g` printf modifier with 
-  [`std::numeric_limits<double>::max_digits10`](https://en.cppreference.com/w/cpp/types/numeric_limits/max_digits10)
-  significant digits. The rationale is to use the shortest representation while still allowing round-tripping.
+- Floating-point numbers are serialized with the fewest digits that read back as the same value (the closest such
+  digits if there are several), in the layout of the `#!c %g` printf modifier: `#!c 1.5`, `#!c 100.0`, `#!c 1e+100`.
+  Doubles are converted with the algorithm of [Żmij](https://github.com/vitaut/zmij), floats with Grisu2, which
+  can write more digits than necessary.

 !!! hint "Notes regarding precision of floating-point numbers"

@@ -26,9 +26,9 @@ Requirements are split into two groups:
    diagnosed with dedicated error messages, and violating most of them results in a compiler error somewhere inside
    the library. Four violations are not caught at compile time at all:

-    - A [`StringType`](#stringtype) whose `data()` is not null-terminated compiles and can silently misparse
-      floating-point numbers, because the lexer may hand the buffer to `#!cpp std::strtod`, which reads up to the
-      terminating null character.
+    - A [`StringType`](#stringtype) whose `data()` is not null-terminated compiles and silently misparses numbers
+      stored as a `#!cpp long double` that is not IEEE 754 binary64 (e.g., the 80-bit x87 format), because the lexer
+      hands the buffer to `#!cpp std::strtold`.
    - A stateful [`AllocatorType`](#allocatortype) compiles and silently ignores its state: allocation, deallocation,
      and [`get_allocator()`](../../api/basic_json/get_allocator.md) each use a different default-constructed instance.
    - The two [cross-specialization conversions](#cross-specialization-conversions) below. These abort on an assertion
@@ -537,16 +537,18 @@ therefore silently changes parse results rather than raising an error. See

 `NumberFloatType` must be one of `#!cpp float`, `#!cpp double`, or `#!cpp long double`:

- The [parser](../parsing/index.md) converts number literals with `#!cpp std::from_chars` or, as a fallback, with
-  `#!cpp std::strtof`, `#!cpp std::strtod`, or `#!cpp std::strtold`; the library provides overloads for exactly these
-  three types.
+- The [parser](../parsing/index.md) converts number literals to `#!cpp float`, `#!cpp double`, and a
+  `#!cpp long double` that is IEEE 754 binary64 itself; other `#!cpp long double` formats are converted with
+  `#!cpp std::from_chars` where available, or with `#!cpp std::strtold`. The library provides overloads for exactly
+  these three types.
 - [`dump`](../../api/basic_json/dump.md) falls back to `#!cpp std::snprintf` with the `%g` and `%Lg` conversion
  specifiers, for which the library likewise provides only `#!cpp double` and `#!cpp long double` overloads
  (`#!cpp float` is promoted to `#!cpp double`).

-If `#!cpp std::numeric_limits<NumberFloatType>` describes an IEEE 754 binary32 or binary64 number, `dump` uses the
-Grisu2 algorithm, which produces the shortest representation that round-trips. Otherwise the `snprintf` fallback with
-`max_digits10` digits is used.
+If `#!cpp std::numeric_limits<NumberFloatType>` describes an IEEE 754 binary64 number, `dump` uses the algorithm of
+Żmij, which produces the shortest representation that round-trips. For IEEE 754 binary32 numbers, it uses Grisu2,
+which produces a short representation that round-trips. Otherwise the `snprintf` fallback with `max_digits10` digits is
+used.

 ### Required for the binary formats

@@ -558,7 +560,7 @@ binary32 or binary64 field and have no encoding for `#!cpp long double`.

 | Type                     | Support                                                                                                               |
 |--------------------------|-----------------------------------------------------------------------------------------------------------------------|
-| `#!cpp double` (default) | full; short round-trip output through Grisu2                                                                          |
+| `#!cpp double` (default) | full; shortest round-trip output through Żmij                                                                         |
 | `#!cpp float`            | full; short round-trip output through Grisu2                                                                          |
 | `#!cpp long double`      | `dump` and `parse` only; the binary format writers do not compile, as they only handle IEEE 754 binary32 and binary64 |
 | any other type           | not usable                                                                                                            |
@@ -331,9 +331,6 @@ An unexpected byte was read in a [binary format](../features/binary_formats/inde
    [json.exception.parse_error.112] parse error at byte 15: syntax error while parsing BSON binary: byte array length cannot be negative, is -1
    ```
    ```
-    [json.exception.parse_error.112] parse error at byte 9: syntax error while parsing CBOR value: negative integer overflow
-    ```
-    ```
    [json.exception.parse_error.112] parse error at byte 5: syntax error while parsing BSON document: document size 6 does not match the number of bytes read (5)
    ```

@@ -599,6 +596,9 @@ During implicit or explicit value conversion, the JSON type must be compatible w
    [json.exception.type_error.302] type must be string, but is object
    ```

+This exception is also thrown with [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](../api/macros/json_use_objects_for_enum_keyed_maps.md)
+if a key of a map with enum keys is not converted to a string, for instance, because the enum is stored as an integer.
+
 ### json.exception.type_error.303

 To retrieve a reference to a value stored in a `basic_json` object with `get_ref`, the type of the reference must match the value type. For instance, for a JSON array, the `ReferenceType` must be `array_t &`.
@@ -791,6 +791,33 @@ The dynamic type of the object cannot be represented in the requested serializat

    Encapsulate the JSON value in an object. That is, instead of serializing `#!json true`, serialize `#!json {"value": true}`

+### json.exception.type_error.318
+
+With [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](../api/macros/json_use_objects_for_enum_keyed_maps.md), a map with enum
+keys is stored as an object. This exception is thrown if two of its keys are converted to the same string, so one of the
+entries would be lost. This happens, for instance, if [`NLOHMANN_JSON_SERIALIZE_ENUM`](../api/macros/nlohmann_json_serialize_enum.md)
+does not list an enumerator and it is therefore converted like the first listed one.
+
+!!! failure "Example message"
+
+    ```
+    [json.exception.type_error.318] duplicate object key 'red'
+    ```
+
+### json.exception.type_error.321
+
+A discarded value (one created by [`parse()`](../api/basic_json/parse.md) with a callback that returns `false` for the
+value, or by default-constructing a [`basic_json`](../api/basic_json/index.md) with
+[`value_t::discarded`](../api/basic_json/value_t.md)) was passed to a binary serialization function, either directly or
+nested in an array or object. There is no way to represent a discarded value in CBOR, MessagePack, UBJSON, BJData, or BSON.
+
+!!! failure "Example message"
+
+    Serializing `#!json [1, 2]` to CBOR, where the second element was discarded by a parser callback:
+    ```
+    [json.exception.type_error.321] cannot serialize discarded value to CBOR
+    ```
+
 ## Out of range

 This exception is thrown in case a library function is called on an input parameter that exceeds the expected range, for instance, in the case of array indices or nonexisting object keys.
@@ -863,13 +890,18 @@ The JSON Patch operations 'remove' and 'add' cannot be applied to the root eleme

 ### json.exception.out_of_range.406

-A parsed number could not be stored as without changing it to NaN or INF.
+A parsed number could not be stored without changing it to NaN or INF. For the binary formats, this happens when a
+finite floating-point number does not fit into [`number_float_t`](../api/basic_json/number_float_t.md), for example a
+double-precision number when `number_float_t` is `#!cpp float`.

-!!! failure "Example message"
+!!! failure "Example messages"

    ```
    number overflow parsing '10E1000'
    ```
+    ```
+    [json.exception.out_of_range.406] syntax error while parsing CBOR value: number overflow
+    ```

 ### json.exception.out_of_range.407

@@ -18,6 +18,8 @@ The class contains the UTF-8 Decoder from Bjoern Hoehrmann which is licensed und

 The class contains a slightly modified version of the Grisu2 algorithm from Florian Loitsch which is licensed under the [MIT License](https://opensource.org/licenses/MIT) (see above). Copyright &copy; 2009 [Florian Loitsch](https://florian.loitsch.com/)

+The class contains a port of the shortest double-to-decimal conversion of [Żmij](https://github.com/vitaut/zmij) by Victor Zverovich, which is licensed under the [MIT License](https://opensource.org/licenses/MIT) (see above). Copyright &copy; 2025 [Victor Zverovich](https://github.com/vitaut)
+
 The class contains a copy of [Hedley](https://nemequ.github.io/hedley/) from Evan Nemerson which is licensed as [CC0-1.0](https://creativecommons.org/publicdomain/zero/1.0/).

-The class contains an adapted version of the Eisel-Lemire algorithm and its table of powers of five from [fast_float](https://github.com/fastfloat/fast_float) by Daniel Lemire and contributors, which is available under the [MIT License](https://opensource.org/licenses/MIT) (used here), the Apache 2.0 License, and the Boost Software License. Copyright &copy; 2021 The fast_float authors
+The class contains an adapted version of the Eisel-Lemire algorithm, its table of powers of five, and its digit comparison for long numbers from [fast_float](https://github.com/fastfloat/fast_float) by Daniel Lemire and contributors, which is available under the [MIT License](https://opensource.org/licenses/MIT) (used here), the Apache 2.0 License, and the Boost Software License. Copyright &copy; 2021 The fast_float authors
@@ -132,6 +132,12 @@ Build the unit tests when [`BUILD_TESTING`](https://cmake.org/cmake/help/latest/

 Enable CI build targets. The exact targets are used during the several CI steps and are subject to change without notice. This option is `OFF` by default.

+### `JSON_DeleteDeprecatedFunctions`
+
+Delete the deprecated functions instead of only deprecating them by defining the macro
+[`JSON_DELETE_DEPRECATED_FUNCTIONS`](../api/macros/json_delete_deprecated_functions.md). This option is `OFF` by
+default.
+
 ### `JSON_Diagnostics`

 Enable [extended diagnostic messages](../home/exceptions.md#extended-diagnostic-messages) by defining macro [`JSON_DIAGNOSTICS`](../api/macros/json_diagnostics.md). This option is `OFF` by default.
@@ -14,6 +14,13 @@ deprecations are annotated with
 [`HEDLEY_DEPRECATED_FOR`](https://nemequ.github.io/hedley/api-reference.html#HEDLEY_DEPRECATED_FOR) to report which
 function to use instead.

+!!! tip "Find all calls of deprecated functions"
+
+    Define [`JSON_DELETE_DEPRECATED_FUNCTIONS`](../api/macros/json_delete_deprecated_functions.md) to `1` (or set the
+    CMake option [`JSON_DeleteDeprecatedFunctions`](cmake.md#json_deletedeprecatedfunctions)) to delete all deprecated
+    functions. Every remaining call then fails to compile, even if deprecation warnings are disabled, so your code is
+    ready for version 4.0.0 once it compiles with the macro.
+
 ### Parsing

 - Function `friend std::istream& operator<<(basic_json&, std::istream&)` is deprecated since 3.0.0. Please use
@@ -41,8 +48,10 @@ function to use instead.
  [`from_ubjson`](../api/basic_json/from_ubjson.md), and [`from_bson`](../api/basic_json/from_bson.md)) via initializer
  lists is deprecated since 3.8.0. Instead, pass two iterators; for instance, call `from_cbor(ptr, ptr+len)` instead of
  `from_cbor({ptr, len})`. Likewise, passing a pointer and a length as two separate arguments to `from_cbor`,
-  `from_msgpack`, `from_ubjson`, and `from_bson` is deprecated since 3.8.0; call `from_cbor(ptr, ptr+len)` instead of
-  `from_cbor(ptr, len)`.
+  `from_msgpack`, `from_ubjson`, and `from_bson` is deprecated since 3.8.0, and to
+  [`from_bjdata`](../api/basic_json/from_bjdata.md) and [`from_bon8`](../api/basic_json/from_bon8.md) since 3.13.0; call
+  `from_cbor(ptr, ptr+len)` instead of `from_cbor(ptr, len)`. These overloads will not be removed in version 4.0.0, but
+  deleted, so a call like `from_cbor(ptr, len)` cannot compile and convert `len` to the `strict` parameter.

    === "Deprecated"
  
@@ -292,6 +292,7 @@ nav:
          - 'JSON_BRACE_INIT_COPY_SEMANTICS': api/macros/json_brace_init_copy_semantics.md
          - 'JSON_CATCH_USER, JSON_THROW_USER, JSON_TRY_USER': api/macros/json_throw_user.md
          - 'JSON_DIAGNOSTICS': api/macros/json_diagnostics.md
+          - 'JSON_DELETE_DEPRECATED_FUNCTIONS': api/macros/json_delete_deprecated_functions.md
          - 'JSON_DIAGNOSTIC_POSITIONS': api/macros/json_diagnostic_positions.md
          - 'JSON_DISABLE_ENUM_SERIALIZATION': api/macros/json_disable_enum_serialization.md
          - 'JSON_DISABLE_TUPLE_REFERENCE_CONVERSION': api/macros/json_disable_tuple_reference_conversion.md
@@ -313,6 +314,7 @@ nav:
          - 'JSON_USE_GLOBAL_UDLS': api/macros/json_use_global_udls.md
          - 'JSON_USE_IMPLICIT_CONVERSIONS': api/macros/json_use_implicit_conversions.md
          - 'JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON': api/macros/json_use_legacy_discarded_value_comparison.md
+          - 'JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS': api/macros/json_use_objects_for_enum_keyed_maps.md
          - 'JSON_USE_SIMDUTF': api/macros/json_use_simdutf.md
          - 'NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE': api/macros/nlohmann_define_derived_type.md
          - 'NLOHMANN_DEFINE_TYPE_INTRUSIVE, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE': api/macros/nlohmann_define_type_intrusive.md
@@ -50,6 +50,10 @@
    #define JSON_STRICT_BINARY_UTF8 0
 #endif

+#ifndef JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
+    #define JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS 0
+#endif
+
 #if JSON_DIAGNOSTICS
    #define NLOHMANN_JSON_ABI_TAG_DIAGNOSTICS _diag
 #else
@@ -92,14 +96,20 @@
    #define NLOHMANN_JSON_ABI_TAG_STRICT_BINARY_UTF8
 #endif

+#if JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
+    #define NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS _ekmo
+#else
+    #define NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS
+#endif
+
 #ifndef NLOHMANN_JSON_NAMESPACE_NO_VERSION
    #define NLOHMANN_JSON_NAMESPACE_NO_VERSION 0
 #endif

 // Construct the namespace ABI tags component
-#define NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g) json_abi ## a ## b ## c ## d ## e ## f ## g
-#define NLOHMANN_JSON_ABI_TAGS_CONCAT(a, b, c, d, e, f, g) \
-    NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g)
+#define NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g, h) json_abi ## a ## b ## c ## d ## e ## f ## g ## h
+#define NLOHMANN_JSON_ABI_TAGS_CONCAT(a, b, c, d, e, f, g, h) \
+    NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g, h)

 #define NLOHMANN_JSON_ABI_TAGS                                       \
    NLOHMANN_JSON_ABI_TAGS_CONCAT(                                   \
@@ -109,7 +119,8 @@
            NLOHMANN_JSON_ABI_TAG_BRACE_INIT_COPY_SEMANTICS,         \
            NLOHMANN_JSON_ABI_TAG_PRECISE_STREAM_POSITION,           \
            NLOHMANN_JSON_ABI_TAG_STRICT_NUL_HANDLING,               \
-            NLOHMANN_JSON_ABI_TAG_STRICT_BINARY_UTF8)
+            NLOHMANN_JSON_ABI_TAG_STRICT_BINARY_UTF8,                \
+            NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS)

 // Construct the namespace version component
 #define NLOHMANN_JSON_NAMESPACE_VERSION_CONCAT_EX(major, minor, patch) \
@@ -39,6 +39,25 @@ inline int count_leading_zeros(std::uint64_t x) noexcept
 #endif
 }

+/// number of trailing zero bits of x (x != 0)
+inline int count_trailing_zeros(std::uint64_t x) noexcept
+{
+#if defined(__GNUC__) || defined(__clang__)
+    return __builtin_ctzll(x);
+#else
+    int n = 0;
+    for (int shift = 32; shift != 0; shift >>= 1)
+    {
+        if ((x << (64 - shift)) == 0)
+        {
+            n += shift;
+            x >>= shift;
+        }
+    }
+    return n;
+#endif
+}
+
 /// the 128-bit product of two 64-bit numbers
 struct uint128_parts
 {
@@ -67,15 +86,21 @@ inline uint128_parts full_multiplication(std::uint64_t a, std::uint64_t b) noexc
 }

 /// eight bytes as a little-endian word (compilers fold this into one load on
-/// little-endian targets)
-inline std::uint64_t read_eight_bytes(const char* p) noexcept
+/// little-endian targets; always inlined, as GCC otherwise calls it in the
+/// number loops)
+JSON_HEDLEY_ALWAYS_INLINE std::uint64_t read_eight_bytes(const unsigned char* b) noexcept
 {
-    const auto* b = reinterpret_cast<const unsigned char*>(p); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
    return static_cast<std::uint64_t>(b[0]) | (static_cast<std::uint64_t>(b[1]) << 8u)
           | (static_cast<std::uint64_t>(b[2]) << 16u) | (static_cast<std::uint64_t>(b[3]) << 24u)
           | (static_cast<std::uint64_t>(b[4]) << 32u) | (static_cast<std::uint64_t>(b[5]) << 40u)
           | (static_cast<std::uint64_t>(b[6]) << 48u) | (static_cast<std::uint64_t>(b[7]) << 56u);
 }

+/// eight bytes as a little-endian word
+JSON_HEDLEY_ALWAYS_INLINE std::uint64_t read_eight_bytes(const char* p) noexcept
+{
+    return read_eight_bytes(reinterpret_cast<const unsigned char*>(p)); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+}
+
 }  // namespace detail
 NLOHMANN_JSON_NAMESPACE_END
@@ -172,7 +172,7 @@ inline void from_json(const BasicJsonType& j, EnumType& e)
          typename BasicJsonType::number_unsigned_t, underlying_type>::type;
    value_type val;
    get_arithmetic_value(j, val);
-    e = static_cast<EnumType>(static_cast<underlying_type>(val));
+    e = static_cast<EnumType>(bool_aware_static_cast<underlying_type>(val));
 }
 #endif  // JSON_DISABLE_ENUM_SERIALIZATION

@@ -530,11 +530,40 @@ void from_json_pair_array_to_map(const BasicJsonType& j, MapType& m)
    }
 }

+// read a map with enum keys from an object, using the enum's own from_json for
+// the keys (e.g., from NLOHMANN_JSON_SERIALIZE_ENUM); this is the form written
+// with JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
+template<typename BasicJsonType, typename Map>
+inline bool from_json_enum_keyed_object(const BasicJsonType& j, Map& m, std::true_type /*key is enum*/)
+{
+    if (!j.is_object())
+    {
+        return false;
+    }
+    m.clear();
+    for (const auto& p : *j.template get_ptr<const typename BasicJsonType::object_t*>())
+    {
+        m.emplace(BasicJsonType(p.first).template get<typename Map::key_type>(), p.second.template get<typename Map::mapped_type>());
+    }
+    return true;
+}
+
+template<typename BasicJsonType, typename Map>
+inline bool from_json_enum_keyed_object(const BasicJsonType& /*j*/, Map& /*m*/, std::false_type /*key is enum*/)
+{
+    return false;
+}
+
 template < typename BasicJsonType, typename Key, typename Value, typename Compare, typename Allocator,
           typename = enable_if_t < !std::is_constructible <
                                        typename BasicJsonType::string_t, Key >::value >>
 void from_json(const BasicJsonType& j, std::map<Key, Value, Compare, Allocator>& m)
 {
+    // NOLINTNEXTLINE(modernize-type-traits) we use C++11
+    if (from_json_enum_keyed_object(j, m, std::is_enum<Key> {}))
+    {
+        return;
+    }
    from_json_pair_array_to_map(j, m);
 }

@@ -543,6 +572,11 @@ template < typename BasicJsonType, typename Key, typename Value, typename Hash,
                                        typename BasicJsonType::string_t, Key >::value >>
 void from_json(const BasicJsonType& j, std::unordered_map<Key, Value, Hash, KeyEqual, Allocator>& m)
 {
+    // NOLINTNEXTLINE(modernize-type-traits) we use C++11
+    if (from_json_enum_keyed_object(j, m, std::is_enum<Key> {}))
+    {
+        return;
+    }
    from_json_pair_array_to_map(j, m);
 }

@@ -11,11 +11,32 @@

 #include <array> // array
 #include <cmath>   // signbit, isfinite
+#include <cstddef> // size_t
 #include <cstdint> // intN_t, uintN_t
 #include <cstring> // memcpy, memmove
 #include <limits> // numeric_limits
 #include <type_traits> // conditional

+#ifdef _MSC_VER
+    #include <cstdlib> // _byteswap_uint64
+#endif
+
+// SSE2 (every x86-64 CPU) and NEON (every 64-bit Arm CPU) convert the 16
+// digits of a double at once
+#if defined(__x86_64__) || (defined(_M_X64) && !defined(_M_ARM64EC))
+    #include <emmintrin.h>
+    #define JSON_DTOA_SSE2 1
+    #define JSON_DTOA_NEON 0
+#elif (defined(__aarch64__) || defined(_M_ARM64)) && !defined(_M_ARM64EC) && !defined(__ARM_BIG_ENDIAN)
+    #include <arm_neon.h>
+    #define JSON_DTOA_SSE2 0
+    #define JSON_DTOA_NEON 1
+#else
+    #define JSON_DTOA_SSE2 0
+    #define JSON_DTOA_NEON 0
+#endif
+
+#include <nlohmann/detail/conversions/zmij.hpp>
 #include <nlohmann/detail/macro_scope.hpp>

 NLOHMANN_JSON_NAMESPACE_BEGIN
@@ -918,6 +939,88 @@ void grisu2(char* buf, int& len, int& decimal_exponent, FloatType value)
    grisu2(buf, len, decimal_exponent, w.minus, w.w, w.plus);
 }

+/*!
+@brief the shortest digits of a positive finite float (other than double): Grisu2
+*/
+template<typename FloatType>
+JSON_HEDLEY_NON_NULL(1)
+void shortest_digits(char* buf, int& len, int& decimal_exponent, FloatType value)
+{
+    grisu2(buf, len, decimal_exponent, value);
+}
+
+/*!
+@brief the shortest digits of a positive finite double: the conversion of
+Zmij (see zmij.hpp), which always finds the shortest digits that read back as
+the same value (Grisu2 does not for about one double in a thousand), and the
+closest of them if there are several
+
+v = buf * 10^decimal_exponent, as for grisu2()
+*/
+JSON_HEDLEY_NON_NULL(1)
+inline void shortest_digits(char* buf, int& len, int& decimal_exponent, double value)
+{
+    static_assert(std::numeric_limits<double>::is_iec559 && std::numeric_limits<double>::digits == 53,
+                  "internal error: the conversion of Zmij needs IEEE 754 binary64 doubles");
+    JSON_ASSERT(std::isfinite(value));
+    JSON_ASSERT(value > 0);
+
+    std::uint64_t bits = 0;
+    std::memcpy(&bits, &value, sizeof(bits));
+    zmij::decimal d = zmij::to_decimal(bits);
+    // without trailing zeros (up to 16): 8, 4, 2, 1 at a time
+    while (d.significand % 100000000 == 0)
+    {
+        d.significand /= 100000000;
+        d.exponent += 8;
+    }
+    if (d.significand % 10000 == 0)
+    {
+        d.significand /= 10000;
+        d.exponent += 4;
+    }
+    if (d.significand % 100 == 0)
+    {
+        d.significand /= 100;
+        d.exponent += 2;
+    }
+    if (d.significand % 10 == 0)
+    {
+        d.significand /= 10;
+        d.exponent += 1;
+    }
+    // at most 17 digits, written from the back two at a time
+    static constexpr const char* pairs =
+        "00010203040506070809101112131415161718192021222324252627282930313233343536373839"
+        "40414243444546474849505152535455565758596061626364656667686970717273747576777879"
+        "8081828384858687888990919293949596979899";
+    std::array<char, 20> digits{};
+    std::size_t n = digits.size();
+    while (d.significand >= 100)
+    {
+        const std::uint64_t two_digits = d.significand % 100; // a variable: GCC calls a cast of the remainder useless where std::uint64_t is std::size_t
+        const auto i = static_cast<std::size_t>(two_digits) * 2;
+        d.significand /= 100;
+        n -= 2;
+        digits[n] = pairs[i];
+        digits[n + 1] = pairs[i + 1];
+    }
+    if (d.significand >= 10)
+    {
+        const auto i = static_cast<std::size_t>(d.significand) * 2;
+        n -= 2;
+        digits[n] = pairs[i];
+        digits[n + 1] = pairs[i + 1];
+    }
+    else
+    {
+        digits[--n] = static_cast<char>('0' + d.significand);
+    }
+    len = static_cast<int>(digits.size() - n);
+    std::memcpy(buf, digits.data() + n, static_cast<std::size_t>(len));
+    decimal_exponent = d.exponent;
+}
+
 /*!
@brief appends a decimal representation of e to buf
@return a pointer to the element following the exponent.
@@ -1047,6 +1150,374 @@ inline char* format_buffer(char* buf, int len, int decimal_exponent,
    return append_exponent(buf, n - 1);
 }

+/// eight decimal digits (a value below 10^8) as bytes 0..9, the first digit
+/// in the most significant byte: three steps that divide all lanes at once
+/// by a multiplication (the conversion of Xiang JunBo, as in Zmij)
+inline std::uint64_t eight_digit_bytes(std::uint64_t abcdefgh) noexcept
+{
+    const std::uint64_t abcd_efgh = abcdefgh + (((std::uint64_t{1} << 32u) - 10000u) * ((abcdefgh * (((std::uint64_t{1} << 40u) / 10000u) + 1u)) >> 40u));
+    const std::uint64_t ab_cd_ef_gh = abcd_efgh + (((std::uint64_t{1} << 16u) - 100u) * (((abcd_efgh * (((std::uint64_t{1} << 19u) / 100u) + 1u)) >> 19u) & 0x7F0000007Fu));
+    return ab_cd_ef_gh + (((std::uint64_t{1} << 8u) - 10u) * (((ab_cd_ef_gh * (((std::uint64_t{1} << 10u) / 10u) + 1u)) >> 10u) & 0x000F000F000F000Fu));
+}
+
+/// store the bytes of v, the most significant one first (one byte swap and
+/// one store where the byte order is known: compilers do not reliably merge
+/// the byte stores once this is inlined)
+inline void store_msb_first(char* p, std::uint64_t v) noexcept
+{
+#if defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+    v = __builtin_bswap64(v);
+    std::memcpy(p, &v, sizeof(v));
+#elif defined(__BYTE_ORDER__) && defined(__ORDER_BIG_ENDIAN__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+    std::memcpy(p, &v, sizeof(v));
+#elif defined(_MSC_VER) // (little-endian on all its targets)
+    v = _byteswap_uint64(v);
+    std::memcpy(p, &v, sizeof(v));
+#else
+    for (unsigned i = 0; i < 8; ++i)
+    {
+        p[i] = static_cast<char>(v >> (56u - (8u * i)));
+    }
+#endif
+}
+
+/*!
+@brief digits * 10^exp for a double, in the layout of format_buffer()
+
+The layout is that of format_buffer() with min_exp -4 and max_exp 15 (the
+digits10 of double). The digits are converted eight at a time and placed
+with fixed-size moves instead of per-digit loops and moves of the buffer.
+
+@param[in] digits  the digits (not 0, at most 17 digits; trailing zeros allowed)
+@param[in] exp     the decimal exponent of the last digit
+@return a pointer past the text; up to 41 bytes at @a first are written
+        (some beyond the returned end)
+*/
+JSON_HEDLEY_NON_NULL(1)
+JSON_HEDLEY_RETURNS_NON_NULL
+inline char* write_decimal(char* first, std::uint64_t digits, int exp) noexcept
+{
+    JSON_ASSERT(digits != 0 && digits < 100000000000000000u);
+    const std::uint64_t upper = digits / 100000000u;
+    const std::uint64_t b0 = upper / 100000000u; // (one digit: it is its own byte)
+    const std::uint64_t b1 = eight_digit_bytes(upper % 100000000u);
+    const std::uint64_t b2 = eight_digit_bytes(digits % 100000000u);
+    // leading and trailing zero digits: zero bytes, counted without division
+    int leading = 16;
+    int zeros = 16;
+    if (b0 != 0)
+    {
+        leading = count_leading_zeros(b0) / 8;
+    }
+    else if (b1 != 0)
+    {
+        leading = 8 + (count_leading_zeros(b1) / 8);
+    }
+    else
+    {
+        leading += count_leading_zeros(b2) / 8;
+    }
+    if (b2 != 0)
+    {
+        zeros = count_trailing_zeros(b2) / 8;
+    }
+    else if (b1 != 0)
+    {
+        zeros = 8 + (count_trailing_zeros(b1) / 8);
+    }
+    // (else: 16, b0 is the one digit that is not 0)
+    // the digits as text at text + leading, then '0's, so that fixed-size
+    // moves need not check how many digits there are
+    std::array<char, 64> text; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+    store_msb_first(text.data(), b0 + 0x3030303030303030u);
+    store_msb_first(text.data() + 8, b1 + 0x3030303030303030u);
+    store_msb_first(text.data() + 16, b2 + 0x3030303030303030u);
+    std::memset(text.data() + 24, '0', 40);
+    const int k = 24 - leading - zeros; // significant digits
+    const int n = k + exp + zeros;      // position of the decimal point after the first digit
+    const char* const s0 = text.data() + leading;
+
+    if (-4 < n && n <= 15)
+    {
+        // "0.[000]digits" (n <= 0) is the digits after 1 - n leading '0's
+        // with the point after the first; "digits[000].0" (n >= k) and
+        // "dig.its" put the point after n characters
+        const int pad = n <= 0 ? 1 - n : 0;
+        const char* const s = s0 - pad;
+        const int len = k + pad;
+        const int point = n + pad;
+        std::memcpy(first, s, 16);
+        std::memcpy(first + point + 1, s + point, 24);
+        first[point] = '.';
+        return first + (point >= len ? point + 2 : len + 1);
+    }
+
+    // d.igitse+XX, with at least two exponent digits (as append_exponent())
+    std::memcpy(first, s0, 16);
+    std::memcpy(first + 2, s0 + 1, 16);
+    first[1] = '.';
+    char* const end = first + (k == 1 ? 1 : k + 1);
+    const int e = n - 1;
+    const auto ea = static_cast<unsigned>(e < 0 ? -e : e);
+    const bool three = ea >= 100;
+    end[0] = 'e';
+    end[1] = e < 0 ? '-' : '+';
+    end[2] = static_cast<char>('0' + (three ? ea / 100 : (ea / 10) % 10));
+    end[3] = static_cast<char>('0' + (three ? (ea / 10) % 10 : ea % 10));
+    end[4] = static_cast<char>('0' + (ea % 10));
+    return end + (three ? 5 : 4);
+}
+
+/*!
+@brief the shortest decimal of a positive double (Zmij), as write_decimal()
+writes it
+
+For a normal double, the shorter candidate has 15 or 16 digits: they are
+converted at once (two halves of eight digits) and followed by the digit
+after them, if there is one, without the multiplication and division by 10
+that counting the digits of one number would take. The fixed layouts move
+the digits after the point by one byte.
+
+@return a pointer past the text; up to 41 bytes at @a first are written
+        (some beyond the returned end)
+*/
+JSON_HEDLEY_NON_NULL(1)
+JSON_HEDLEY_RETURNS_NON_NULL
+inline char* write_shortest(char* first, const zmij::shortest_decimal d) noexcept
+{
+    const std::uint64_t sig = d.integral;
+    if (JSON_HEDLEY_UNLIKELY(sig < 100000000000000u || sig >= 10000000000000000u))
+    {
+        // (subnormals)
+        return d.has_digit ? write_decimal(first, (sig * 10) + d.digit, d.exponent) : write_decimal(first, sig, d.exponent + 1);
+    }
+    const bool sixteen = sig >= 1000000000000000u; // (else 15 digits)
+    const int last = d.has_digit ? d.digit : 0;
+    const std::uint64_t upper = sig / 100000000u;
+#if JSON_DTOA_SSE2
+    // NOLINTBEGIN(portability-simd-intrinsics)
+    // the two halves in the 64-bit lanes, each as abcd * 2^32 + efgh, then as
+    // bytes (as eight_digit_bytes(), one lane each)
+    const __m128i x = _mm_set_epi64x(static_cast<long long>(sig - (upper * 100000000u)), static_cast<long long>(upper));
+    const __m128i abcd = _mm_srli_epi64(_mm_mul_epu32(x, _mm_set1_epi64x(109951163)), 40); // 2^40 / 10000 + 1
+    const __m128i abcd_efgh = _mm_add_epi64(x, _mm_mul_epu32(abcd, _mm_set1_epi64x(4294957296))); // 2^32 - 10000
+    // 32-bit lanes in the order of the text: abcd, efgh of both halves
+    const __m128i fours = _mm_shuffle_epi32(abcd_efgh, _MM_SHUFFLE(2, 3, 0, 1));
+    const __m128i ab = _mm_srli_epi16(_mm_mulhi_epu16(fours, _mm_set1_epi32(5243)), 3);
+    const __m128i ab_cd = _mm_or_si128(_mm_slli_epi32(_mm_sub_epi16(fours, _mm_mullo_epi16(ab, _mm_set1_epi32(100))), 16), ab);
+    // 16-bit lanes ab (< 100) -> bytes a, b: 256 * ab - 2559 * (ab / 10)
+    const __m128i bytes = _mm_sub_epi16(_mm_slli_epi16(ab_cd, 8), _mm_mullo_epi16(_mm_set1_epi16(2559), _mm_mulhi_epu16(ab_cd, _mm_set1_epi16(6554))));
+    // the last digit that is not 0 (sig is not 0)
+    const auto nonzero = static_cast<std::uint64_t>(_mm_movemask_epi8(_mm_cmpgt_epi8(bytes, _mm_setzero_si128())));
+    const int digits = 63 - count_leading_zeros(nonzero) + (sixteen ? 1 : 0); // without trailing zeros
+    const __m128i chars = _mm_add_epi8(bytes, _mm_set1_epi8('0'));
+    // the 16 characters from the first digit
+    const __m128i s = sixteen ? chars : _mm_or_si128(_mm_srli_si128(chars, 1), _mm_slli_si128(_mm_cvtsi32_si128('0' + last), 15));
+    const char s16 = static_cast<char>(sixteen ? '0' + last : '0'); // the 17th
+    const auto store_16 = [&s](char* p) noexcept
+    {
+        std::memcpy(p, &s, 16);
+    };
+    const char first_digit = static_cast<char>(_mm_cvtsi128_si32(s));
+    // NOLINTEND(portability-simd-intrinsics)
+#elif JSON_DTOA_NEON
+    // as with SSE2: the halves in 32-bit lanes, then abcd, efgh of both
+    const uint32x2_t halves = vcreate_u32(upper | ((sig - (upper * 100000000u)) << 32u));
+    const uint32x2_t abcd = vmovn_u64(vshrq_n_u64(vmull_n_u32(halves, static_cast<std::uint32_t>(((std::uint64_t{1} << 40u) / 10000u) + 1u)), 40));
+    const uint32x2_t efgh = vmls_n_u32(halves, abcd, 10000u);
+    const uint32x4_t fours = vcombine_u32(vzip1_u32(abcd, efgh), vzip2_u32(abcd, efgh));
+    const uint32x4_t ab = vshrq_n_u32(vmulq_n_u32(fours, 5243u), 19);
+    const uint16x8_t ab_cd = vreinterpretq_u16_u32(vorrq_u32(ab, vshlq_n_u32(vmlsq_n_u32(fours, ab, 100u), 16)));
+    const uint16x8_t tens = vshrq_n_u16(vmulq_n_u16(ab_cd, 103u), 10);
+    const uint8x16_t bytes = vreinterpretq_u8_u16(vorrq_u16(tens, vshlq_n_u16(vmlsq_n_u16(ab_cd, tens, 10u), 8)));
+    // the last digit that is not 0 (sig is not 0): a nibble per byte
+    const std::uint64_t nonzero = vget_lane_u64(vreinterpret_u64_u8(vshrn_n_u16(vreinterpretq_u16_u8(vtstq_u8(bytes, bytes)), 4)), 0);
+    const int digits = ((63 - count_leading_zeros(nonzero)) / 4) + (sixteen ? 1 : 0); // without trailing zeros
+    const uint8x16_t chars = vaddq_u8(bytes, vdupq_n_u8('0'));
+    // the 16 characters from the first digit
+    const uint8x16_t s = sixteen ? chars : vextq_u8(chars, vdupq_n_u8(static_cast<std::uint8_t>('0' + last)), 1);
+    const char s16 = static_cast<char>(sixteen ? '0' + last : '0'); // the 17th
+    const auto store_16 = [&s](char* p) noexcept
+    {
+        vst1q_u8(reinterpret_cast<std::uint8_t*>(p), s); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+    };
+    const auto first_digit = static_cast<char>(vgetq_lane_u8(s, 0));
+#else
+    const std::uint64_t hi = eight_digit_bytes(upper);
+    const std::uint64_t lo = eight_digit_bytes(sig - (upper * 100000000u));
+    // trailing zero digits: zero bytes (sig is not 0)
+    const int zeros = lo != 0 ? count_trailing_zeros(lo) / 8 : 8 + (count_trailing_zeros(hi) / 8);
+    const int digits = 15 - zeros + (sixteen ? 1 : 0); // without trailing zeros
+    // the 16 characters from the first digit
+    const std::uint64_t s_hi = (sixteen ? hi : (hi << 8u) | (lo >> 56u)) + 0x3030303030303030u;
+    const std::uint64_t s_lo = (sixteen ? lo : (lo << 8u) | static_cast<std::uint64_t>(last)) + 0x3030303030303030u;
+    const char s16 = static_cast<char>(sixteen ? '0' + last : '0'); // the 17th
+    const auto store_16 = [s_hi, s_lo](char* p) noexcept
+    {
+        store_msb_first(p, s_hi);
+        store_msb_first(p + 8, s_lo);
+    };
+    const auto first_digit = static_cast<char>(s_hi >> 56u);
+#endif
+    const int len = d.has_digit ? 16 + (sixteen ? 1 : 0) : digits; // significant digits
+    const int n = 16 + (sixteen ? 1 : 0) + d.exponent;           // digits before the point
+
+    if (JSON_HEDLEY_LIKELY(n >= 1 && n <= 15))
+    {
+        // "dig.its" and "digits[000].0": the digits after the point move by
+        // one byte ('0's follow the digits)
+#if JSON_DTOA_SSE2
+        // NOLINTBEGIN(portability-simd-intrinsics)
+        // (in the register: reading the digits back from memory right after
+        // storing them waits until the stores are done)
+        const __m128i at = _mm_set1_epi8(static_cast<char>(n));
+        const __m128i index = _mm_setr_epi8(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15);
+        const __m128i before = _mm_cmpgt_epi8(at, index);
+        const __m128i after = _mm_cmpgt_epi8(index, at);
+        const __m128i text = _mm_or_si128(_mm_or_si128(_mm_and_si128(s, before), _mm_and_si128(_mm_slli_si128(s, 1), after)),
+                                          _mm_andnot_si128(_mm_or_si128(before, after), _mm_set1_epi8('.')));
+        std::memcpy(first, &text, 16);
+        first[16] = static_cast<char>(_mm_extract_epi16(s, 7) >> 8);
+        first[17] = s16;
+        // NOLINTEND(portability-simd-intrinsics)
+#elif JSON_DTOA_NEON
+        const uint8x16_t index = vcombine_u8(vcreate_u8(0x0706050403020100u), vcreate_u8(0x0F0E0D0C0B0A0908u));
+        const uint8x16_t at = vdupq_n_u8(static_cast<std::uint8_t>(n));
+        const uint8x16_t after_point = vbslq_u8(vcgtq_u8(index, at), vextq_u8(vdupq_n_u8(0), s, 15), vdupq_n_u8('.'));
+        vst1q_u8(reinterpret_cast<std::uint8_t*>(first), vbslq_u8(vcltq_u8(index, at), s, after_point)); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+        first[16] = static_cast<char>(vgetq_lane_u8(s, 15));
+        first[17] = s16;
+#else
+        store_16(first);
+        first[16] = s16;
+        std::uint64_t after_point[2]; // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays,cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        std::memcpy(after_point, first + n, 16);
+        std::memcpy(first + n + 1, after_point, 16);
+        first[n] = '.';
+#endif
+        return first + (n >= len ? n + 2 : len + 1);
+    }
+    if (n <= 0 && n > -4)
+    {
+        // "0.[000]digits"
+        std::memset(first, '0', 8);
+        first[1] = '.';
+        store_16(first + 2 - n);
+        first[18 - n] = s16;
+        return first + 2 - n + len;
+    }
+    // d.igitse+XX, with at least two exponent digits (as append_exponent())
+    store_16(first + 1);
+    first[17] = s16;
+    first[0] = first_digit;
+    first[1] = '.';
+    char* const end = first + (len == 1 ? 1 : len + 1);
+    const int e = n - 1;
+    const auto ea = static_cast<unsigned>(e < 0 ? -e : e);
+    const bool three = ea >= 100;
+    end[0] = 'e';
+    end[1] = e < 0 ? '-' : '+';
+    end[2] = static_cast<char>('0' + (three ? ea / 100 : (ea / 10) % 10));
+    end[3] = static_cast<char>('0' + (three ? (ea / 10) % 10 : ea % 10));
+    end[4] = static_cast<char>('0' + (ea % 10));
+    return end + (three ? 5 : 4);
+}
+
+/// the powers of ten up to 10^16
+inline const std::array<std::uint64_t, 17>& powers_of_ten_16() noexcept
+{
+    static const std::array<std::uint64_t, 17> powers =
+    {
+        {
+            1u, 10u, 100u, 1000u, 10000u, 100000u, 1000000u, 10000000u, 100000000u, 1000000000u, 10000000000u,
+            100000000000u, 1000000000000u, 10000000000000u, 100000000000000u, 1000000000000000u, 10000000000000000u
+        }
+    };
+    return powers;
+}
+
+/*!
+@brief digits * 10^exp, as write_decimal() writes it, for the digits of a
+double that need no conversion (count digits, at most 15, the first not 0;
+trailing zeros allowed): extended to 16 digits and written by write_shortest()
+
+@return a pointer past the text; up to 41 bytes at @a first are written
+        (some beyond the returned end)
+*/
+JSON_HEDLEY_NON_NULL(1)
+JSON_HEDLEY_RETURNS_NON_NULL
+inline char* write_short_decimal(char* first, std::uint64_t digits, int count, int exp) noexcept
+{
+    JSON_ASSERT(digits >= powers_of_ten_16()[static_cast<std::size_t>(count - 1)] && count <= 15);
+    const int scale = 16 - count;
+    return write_shortest(first, zmij::shortest_decimal{digits * powers_of_ten_16()[static_cast<std::size_t>(scale)], exp - scale - 1, 0, false});
+}
+
+/// as write_short_decimal(), counting the digits (not 0, less than 10^15)
+JSON_HEDLEY_NON_NULL(1)
+JSON_HEDLEY_RETURNS_NON_NULL
+inline char* write_short_decimal(char* first, std::uint64_t digits, int exp) noexcept
+{
+    JSON_ASSERT(digits != 0 && digits < 1000000000000000u);
+    // floor(log10(2^bits)) + 1 digits, or one less
+    const int log2_bound = ((64 - count_leading_zeros(digits)) * 1233) >> 12;
+    const int count = log2_bound + (digits >= powers_of_ten_16()[static_cast<std::size_t>(log2_bound)] ? 1 : 0);
+    return write_short_decimal(first, digits, count, exp);
+}
+
+/// a positive finite float (other than double): Grisu2 and format_buffer()
+template<typename FloatType>
+JSON_HEDLEY_NON_NULL(1, 2)
+JSON_HEDLEY_RETURNS_NON_NULL
+char* write_positive(char* first, const char* last, FloatType value)
+{
+    JSON_ASSERT(last - first >= std::numeric_limits<FloatType>::max_digits10);
+
+    // Compute v = buffer * 10^decimal_exponent.
+    // The decimal digits are stored in the buffer, which needs to be interpreted
+    // as an unsigned decimal integer.
+    // len is the length of the buffer, i.e., the number of decimal digits.
+    int len = 0;
+    int decimal_exponent = 0;
+    shortest_digits(first, len, decimal_exponent, value);
+
+    JSON_ASSERT(len <= std::numeric_limits<FloatType>::max_digits10);
+
+    // Format the buffer like printf("%.*g", prec, value)
+    constexpr int kMinExp = -4;
+    // Use digits10 here to increase compatibility with version 2.
+    constexpr int kMaxExp = std::numeric_limits<FloatType>::digits10;
+
+    JSON_ASSERT(last - first >= kMaxExp + 2);
+    JSON_ASSERT(last - first >= 2 + (-kMinExp - 1) + std::numeric_limits<FloatType>::max_digits10);
+    JSON_ASSERT(last - first >= std::numeric_limits<FloatType>::max_digits10 + 6);
+
+    return format_buffer(first, len, decimal_exponent, kMinExp, kMaxExp);
+}
+
+/// a positive finite double: the shortest digits (Zmij), laid out by
+/// write_shortest() (through a local buffer if [first, last) is shorter than
+/// the 41 bytes it may write)
+JSON_HEDLEY_NON_NULL(1, 2)
+JSON_HEDLEY_RETURNS_NON_NULL
+inline char* write_positive(char* first, const char* last, double value)
+{
+    static_assert(std::numeric_limits<double>::is_iec559 && std::numeric_limits<double>::digits == 53,
+                  "internal error: the conversion of Zmij needs IEEE 754 binary64 doubles");
+    std::uint64_t bits = 0;
+    std::memcpy(&bits, &value, sizeof(bits));
+    const zmij::shortest_decimal d = zmij::to_shortest(bits);
+    if (JSON_HEDLEY_LIKELY(last - first >= 41))
+    {
+        return write_shortest(first, d);
+    }
+    std::array<char, 64> buf; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+    const auto len = static_cast<std::size_t>(write_shortest(buf.data(), d) - buf.data());
+    JSON_ASSERT(static_cast<std::size_t>(last - first) >= len);
+    std::memcpy(first, buf.data(), len);
+    return first + len;
+}
+
 }  // namespace dtoa_impl

 /*!
@@ -1064,7 +1535,6 @@ JSON_HEDLEY_NON_NULL(1, 2)
 JSON_HEDLEY_RETURNS_NON_NULL
 char* to_chars(char* first, const char* last, FloatType value)
 {
-    static_cast<void>(last); // maybe unused - fix warning
    JSON_ASSERT(std::isfinite(value));

    // Use signbit(value) instead of (value < 0) since signbit works for -0.
@@ -1090,28 +1560,7 @@ char* to_chars(char* first, const char* last, FloatType value)
    JSON_HEDLEY_DIAGNOSTIC_POP
 #endif

-    JSON_ASSERT(last - first >= std::numeric_limits<FloatType>::max_digits10);
-
-    // Compute v = buffer * 10^decimal_exponent.
-    // The decimal digits are stored in the buffer, which needs to be interpreted
-    // as an unsigned decimal integer.
-    // len is the length of the buffer, i.e., the number of decimal digits.
-    int len = 0;
-    int decimal_exponent = 0;
-    dtoa_impl::grisu2(first, len, decimal_exponent, value);
-
-    JSON_ASSERT(len <= std::numeric_limits<FloatType>::max_digits10);
-
-    // Format the buffer like printf("%.*g", prec, value)
-    constexpr int kMinExp = -4;
-    // Use digits10 here to increase compatibility with version 2.
-    constexpr int kMaxExp = std::numeric_limits<FloatType>::digits10;
-
-    JSON_ASSERT(last - first >= kMaxExp + 2);
-    JSON_ASSERT(last - first >= 2 + (-kMinExp - 1) + std::numeric_limits<FloatType>::max_digits10);
-    JSON_ASSERT(last - first >= std::numeric_limits<FloatType>::max_digits10 + 6);
-
-    return dtoa_impl::format_buffer(first, len, decimal_exponent, kMinExp, kMaxExp);
+    return dtoa_impl::write_positive(first, last, value);
 }

 }  // namespace detail
@@ -23,6 +23,7 @@
 #include <valarray> // valarray
 #include <vector> // vector

+#include <nlohmann/detail/exceptions.hpp>
 #include <nlohmann/detail/iterators/iteration_proxy.hpp>
 #include <nlohmann/detail/meta/cpp_future.hpp>
 #include <nlohmann/detail/meta/std_fs.hpp>
@@ -286,9 +287,20 @@ struct external_constructor<value_t::object>
 /////////////

 #ifdef JSON_HAS_CPP_17
+// whether storing the value of a std::optional<T> cannot throw; MSVC 2017
+// evaluates std::is_nothrow_assignable as true even if T's to_json throws, so
+// the exception would call std::terminate (#5642)
+#if defined(_MSC_VER) && !defined(__clang__) && _MSC_VER < 1920
+    template<typename BasicJsonType, typename T>
+    using is_nothrow_optional_to_json = std::false_type;
+#else
+    template<typename BasicJsonType, typename T>
+    using is_nothrow_optional_to_json = std::is_nothrow_assignable<BasicJsonType&, const T&>;
+#endif
+
 template<typename BasicJsonType, typename T,
         enable_if_t<std::is_constructible<BasicJsonType, T>::value, int> = 0>
-void to_json(BasicJsonType& j, const std::optional<T>& opt) noexcept(std::is_nothrow_assignable<BasicJsonType&, const T&>::value)
+void to_json(BasicJsonType& j, const std::optional<T>& opt) noexcept(is_nothrow_optional_to_json<BasicJsonType, T>::value)
 {
    if (opt.has_value())
    {
@@ -364,7 +376,7 @@ inline void to_json(BasicJsonType& j, EnumType e) noexcept
 {
    using underlying_type = typename std::underlying_type<EnumType>::type;
    static constexpr value_t integral_value_t = std::is_unsigned<underlying_type>::value ? value_t::number_unsigned : value_t::number_integer;
-    external_constructor<integral_value_t>::construct(j, static_cast<underlying_type>(e));
+    external_constructor<integral_value_t>::construct(j, bool_aware_static_cast<underlying_type>(e));
 }
 #endif  // JSON_DISABLE_ENUM_SERIALIZATION

@@ -384,6 +396,9 @@ template < typename BasicJsonType, typename CompatibleArrayType,
                         !is_basic_json<CompatibleArrayType>::value
 #if JSON_HAS_RANGE_VIEW_CONVERSION
    && !is_compatible_range_view<CompatibleArrayType>::value
+#endif
+#if JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
+    && !is_enum_keyed_map<CompatibleArrayType>::value
 #endif
                         ,
                         int > = 0 >
@@ -438,6 +453,33 @@ inline void to_json(BasicJsonType& j, const CompatibleObjectType& obj)
    external_constructor<value_t::object>::construct(j, obj);
 }

+#if JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
+// store a map with enum keys as an object, using the enum's own to_json for the
+// keys (e.g., from NLOHMANN_JSON_SERIALIZE_ENUM); without the macro, such maps
+// are stored as arrays of [key, value] pairs
+template < typename BasicJsonType, typename EnumKeyedMap,
+           enable_if_t < is_enum_keyed_map<EnumKeyedMap>::value&& !is_basic_json<EnumKeyedMap>::value, int > = 0 >
+inline void to_json(BasicJsonType& j, const EnumKeyedMap& map)
+{
+    typename BasicJsonType::object_t obj;
+    for (const auto& p : map)
+    {
+        BasicJsonType key = p.first;
+        if (JSON_HEDLEY_UNLIKELY(!key.is_string()))
+        {
+            JSON_THROW(type_error::create(302, concat("type must be string, but is ", key.type_name()), &key));
+        }
+
+        auto& key_string = *key.template get_ptr<typename BasicJsonType::string_t*>();
+        if (JSON_HEDLEY_UNLIKELY(!obj.emplace(key_string, BasicJsonType(p.second)).second))
+        {
+            JSON_THROW(type_error::create(318, concat("duplicate object key '", key_string, "'"), &key));
+        }
+    }
+    external_constructor<value_t::object>::construct(j, std::move(obj));
+}
+#endif
+
 template<typename BasicJsonType>
 inline void to_json(BasicJsonType& j, typename BasicJsonType::object_t&& obj)
 {
@@ -0,0 +1,238 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2025 Victor Zverovich <https://github.com/vitaut/zmij>
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#pragma once
+
+#include <array> // array
+#include <cstddef> // size_t
+#include <cstdint> // uint32_t, uint64_t
+
+#include <nlohmann/detail/abi_macros.hpp>
+#include <nlohmann/detail/bit_ops.hpp>
+#include <nlohmann/detail/input/pow5_table.hpp>
+#include <nlohmann/detail/macro_scope.hpp>
+
+NLOHMANN_JSON_NAMESPACE_BEGIN
+namespace detail
+{
+
+/*!
+@brief the shortest decimal representation of a double
+
+A C++11 port of the conversion of Zmij by Victor Zverovich
+(https://github.com/vitaut/zmij, MIT license): the shortest decimal in the
+rounding interval of a double, the closest one if there are several. Zmij
+credits Xiang JunBo (producing the shorter candidate without a division) and
+Dougall Johnson (the compressed powers of ten). The powers of ten are taken
+from the table for number parsing (pow5_table.hpp) where it holds them, and
+computed from the compressed tables of Zmij beyond it.
+*/
+namespace zmij
+{
+
+/// significand * 10^exponent
+struct decimal
+{
+    std::uint64_t significand;
+    int exponent;
+};
+
+/// the compressed powers of ten of Zmij
+inline const std::array<std::uint64_t, 28>& pow10_minor() noexcept
+{
+    static const std::array<std::uint64_t, 28> table =
+    {
+        {
+            0x8000000000000000u, 0xa000000000000000u, 0xc800000000000000u, 0xfa00000000000000u, 0x9c40000000000000u,
+            0xc350000000000000u, 0xf424000000000000u, 0x9896800000000000u, 0xbebc200000000000u, 0xee6b280000000000u,
+            0x9502f90000000000u, 0xba43b74000000000u, 0xe8d4a51000000000u, 0x9184e72a00000000u, 0xb5e620f480000000u,
+            0xe35fa931a0000000u, 0x8e1bc9bf04000000u, 0xb1a2bc2ec5000000u, 0xde0b6b3a76400000u, 0x8ac7230489e80000u,
+            0xad78ebc5ac620000u, 0xd8d726b7177a8000u, 0x878678326eac9000u, 0xa968163f0a57b400u, 0xd3c21bcecceda100u,
+            0x84595161401484a0u, 0xa56fa5b99019a5c8u, 0xcecb8f27f4200f3au
+        }
+    };
+    return table;
+}
+
+/// (high, low) pairs
+inline const std::array<std::uint64_t, 50>& pow10_major() noexcept
+{
+    static const std::array<std::uint64_t, 50> table =
+    {
+        {
+            0xaddcb9e83c6b1793u, 0xdf4abe242a1bbf3eu, 0xaf8e5410288e1b6fu, 0x07ecf0ae5ee44ddau, 0xb1442798f49ffb4au, 0x99cd11cfdf41779du,
+            0xb2fe3f0b8599ef07u, 0x861fa7e6dcb4aa15u, 0xb4bca50b065abe63u, 0x0fed077a756b53aau, 0xb67f6455292cbf08u, 0x1a3bc84c17b1d543u,
+            0xb84687c269ef3bfbu, 0x3d5d514f40eea742u, 0xba121a4650e4ddebu, 0x92f34d62616ce413u, 0xbbe226efb628afeau, 0x890489f70a55368cu,
+            0xbdb6b8e905cb600fu, 0x5400e987bbc1c921u, 0xbf8fdb78849a5f96u, 0xde98520472bdd034u, 0xc16d9a0095928a27u, 0x75b7053c0f178294u,
+            0xc350000000000000u, 0x0000000000000000u, 0xc5371912364ce305u, 0x6c28000000000000u, 0xc722f0ef9d80aad6u, 0x424d3ad2b7b97ef6u,
+            0xc913936dd571c84cu, 0x03bc3a19cd1e38eau, 0xcb090c8001ab551cu, 0x5cadf5bfd3072cc6u, 0xcd036837130890a1u, 0x36dba887c37a8c10u,
+            0xcf02b2c21207ef2eu, 0x94f967e45e03f4bcu, 0xd106f86e69d785c7u, 0xe13336d701beba52u, 0xd31045a8341ca07cu, 0x1ede48111209a051u,
+            0xd51ea6fa85785631u, 0x552a74227f3ea566u, 0xd732290fbacaf133u, 0xa97c177947ad4096u, 0xd94ad8b1c7380874u, 0x18375281ae7822bdu,
+            0xdb68c2ca82ed2a05u, 0xa67398db9f6820e1u
+        }
+    };
+    return table;
+}
+
+/// one bit per power: whether the computed value is one unit too large
+inline const std::array<std::uint32_t, 21>& pow10_fixups() noexcept
+{
+    static const std::array<std::uint32_t, 21> table =
+    {
+        {
+            0x8d8fc810u, 0x06100293u, 0x19000000u, 0x00100000u, 0x00000908u, 0x00000000u, 0x04e00300u, 0x3807e0b2u, 0x3d83d793u, 0x0006f5ccu,
+            0x00000000u, 0xffff0000u, 0x8076337du, 0x4ff45ba0u, 0x09405033u, 0x034376d9u, 0x09000000u, 0x4e100501u, 0x076d14dcu, 0xf964f45eu,
+            0x0000003du
+        }
+    };
+    return table;
+}
+
+/// the 128-bit significand of 10^k, rounded down, for k in [-307, 341]
+/// (compute_pow10 of Zmij)
+inline uint128_parts compute_pow10(int k) noexcept
+{
+    const auto i = static_cast<unsigned>(k + 307);
+    const std::uint64_t m = pow10_minor()[(i + 24) % 28];
+    const std::size_t j = 2 * static_cast<std::size_t>((i + 24) / 28);
+    const std::uint64_t h_hi = pow10_major()[j];
+    const std::uint64_t h_lo = pow10_major()[j + 1];
+    const std::uint64_t h1 = full_multiplication(h_lo, m).high;
+    const std::uint64_t c0 = h_lo * m;
+    const std::uint64_t c1 = h1 + (h_hi * m);
+    const std::uint64_t c2 = (c1 < h1 ? 1u : 0u) + full_multiplication(h_hi, m).high;
+    uint128_parts r{};
+    if ((c2 >> 63u) != 0)
+    {
+        r.high = c2;
+        r.low = c1;
+    }
+    else
+    {
+        r.high = (c2 << 1u) | (c1 >> 63u);
+        r.low = (c1 << 1u) | (c0 >> 63u);
+    }
+    r.low -= (pow10_fixups()[i >> 5u] >> (i & 31u)) & 1u;
+    return r;
+}
+
+/// The 128-bit significand of 10^k, rounded down, for k in [-342, 341].
+/// Up to 10^308, the table for number parsing holds the same significands
+/// (those of 5^k), except for k in [-27, -1], where it holds them one unit
+/// larger (as the Eisel-Lemire algorithm needs them).
+inline uint128_parts pow10(int k) noexcept
+{
+    if (k > pow5_128_largest_power)
+    {
+        return compute_pow10(k); // (only for the smallest doubles)
+    }
+    const auto i = 2 * static_cast<std::size_t>(k - pow5_128_smallest_power);
+    uint128_parts r{pow5_128()[i + 1], pow5_128()[i]};
+    const std::uint64_t adjust = static_cast<unsigned>(k + 27) < 27u ? 1u : 0u;
+    r.high -= r.low < adjust ? 1u : 0u;
+    r.low -= adjust;
+    return r;
+}
+
+/// (x_hi * 2^64 + x_lo) * y >> 64, as 128 bits
+inline uint128_parts umul192_hi128(std::uint64_t x_hi, std::uint64_t x_lo, std::uint64_t y) noexcept
+{
+    const uint128_parts p = full_multiplication(x_hi, y);
+    uint128_parts r{};
+    r.low = p.low + full_multiplication(x_lo, y).high;
+    r.high = p.high + (r.low < p.low ? 1u : 0u);
+    return r;
+}
+
+/// (x * y + c) >> 64
+inline std::uint64_t umul128_add_hi64(std::uint64_t x, std::uint64_t y, std::uint64_t c) noexcept
+{
+    const uint128_parts p = full_multiplication(x, y);
+    return p.high + (p.low + c < p.low ? 1u : 0u);
+}
+
+/// the result of Zmij: the shorter candidate and, if that is outside the
+/// rounding interval, the digit after it (16 bytes: returned in registers)
+struct shortest_decimal
+{
+    std::uint64_t integral;  ///< the shorter candidate (15 or 16 digits for normal doubles)
+    int exponent;            ///< the decimal exponent of the digit after it
+    unsigned char digit;     ///< the digit after it (if has_digit)
+    bool has_digit;          ///< whether the shortest decimal is integral * 10 + digit
+};
+
+/// The shortest decimal in the rounding interval of a positive finite double
+/// given by its bits, the closest one if there are several (to_decimal of
+/// Zmij, which keeps the last digit apart: the 15 or 16 digits before it can be
+/// converted without a multiplication by 10 first). Always inlined: GCC
+/// otherwise calls it, and its result goes through memory.
+JSON_HEDLEY_ALWAYS_INLINE shortest_decimal to_shortest(std::uint64_t bits) noexcept
+{
+    constexpr int extra_shift = 9;
+    const auto raw_exp = static_cast<int>((bits >> 52u) & 0x7FFu);
+    std::uint64_t bin_sig = bits & ((std::uint64_t{1} << 52u) - 1);
+    // a power of two has a narrower interval below (except the smallest normal)
+    const bool regular = bin_sig != 0 || raw_exp <= 1;
+    const int bin_exp = (raw_exp == 0 ? 1 : raw_exp) - 1075;
+    if (raw_exp != 0)
+    {
+        bin_sig |= std::uint64_t{1} << 52u;
+    }
+    // floor(log10(2^bin_exp)), or floor(log10(3/4 * 2^bin_exp)) for the irregular case
+    const int dec_exp = ((bin_exp * 315653) - (regular ? 0 : 131072)) >> 20;
+    // scaled by 10^(-dec_exp - 1): the integral part is the shorter candidate
+    const int shift = bin_exp + ((-(dec_exp + 1) * 217707) >> 16) + 1 + extra_shift;
+    const uint128_parts p10 = pow10(-dec_exp - 1);
+    const uint128_parts p = umul192_hi128(p10.high, p10.low, bin_sig << static_cast<unsigned>(shift));
+    std::uint64_t integral = p.high >> static_cast<unsigned>(extra_shift);
+    const std::uint64_t fractional = (p.high << static_cast<unsigned>(64 - extra_shift)) | (p.low >> static_cast<unsigned>(extra_shift));
+    std::uint64_t digit = 0;
+    bool round_up = false;
+    bool round_down = false;
+    if (JSON_HEDLEY_LIKELY(regular))
+    {
+        const std::uint64_t half_ulp = (p10.high >> static_cast<unsigned>(extra_shift + 1 - shift)) + (1 - (bin_sig & 1u));
+        round_up = fractional + half_ulp < fractional;
+        round_down = half_ulp > fractional;
+        // the last digit of the longer candidate, rounded to nearest
+        digit = umul128_add_hi64(fractional, 10, (std::uint64_t{1} << 63u) + 6);
+        if (fractional == (std::uint64_t{1} << 62u))
+        {
+            digit = 2; // 2.5 rounds to 2
+        }
+    }
+    else
+    {
+        const std::uint64_t half_ulp = p10.high >> static_cast<unsigned>(extra_shift + 1 - shift);
+        round_up = half_ulp > ~std::uint64_t{0} - fractional;
+        round_down = (half_ulp >> 1u) > fractional;
+        digit = umul128_add_hi64(fractional, 10, (std::uint64_t{1} << 63u) - 1);
+        const std::uint64_t lowest = umul128_add_hi64(fractional - (half_ulp >> 1u), 10, ~std::uint64_t{0});
+        digit = digit < lowest ? lowest : digit;
+    }
+    integral += round_up ? 1u : 0u;
+    // if the shorter candidate is outside the rounding interval: one digit more
+    return shortest_decimal{integral, dec_exp, static_cast<unsigned char>(digit), !round_up && !round_down};
+}
+
+/// The shortest decimal in the rounding interval of a positive finite double
+/// given by its bits, as one number. The significand can end in zeros.
+inline decimal to_decimal(std::uint64_t bits) noexcept
+{
+    const shortest_decimal d = to_shortest(bits);
+    if (d.has_digit)
+    {
+        return decimal{(d.integral * 10) + d.digit, d.exponent};
+    }
+    return decimal{d.integral, d.exponent + 1};
+}
+
+}  // namespace zmij
+}  // namespace detail
+NLOHMANN_JSON_NAMESPACE_END
@@ -221,6 +221,44 @@ class lexer : public lexer_base<BasicJsonType>
    // scan functions
    /////////////////////

+    /// contiguous input: try to decode the 4 hex digits following `\\u`
+    /// directly from the input buffer via hex_codepoint(), instead of 4 calls
+    /// to get(). On success, advances the adapter and the position counters
+    /// exactly as those 4 get() calls would (a hex digit is never '\n', so
+    /// only the flat counters move) and leaves @a current holding the last of
+    /// the 4 digits, just as the last such get() would; the codepoint is
+    /// written to @a out. Makes no state change and returns false - for a
+    /// pending unget, fewer than 4 remaining bytes, or any of the 4 bytes not
+    /// being a hex digit - so the caller falls back unchanged to the
+    /// per-character loop, which then reports the same diagnostic (stopping
+    /// at the first invalid digit) as before this optimization.
+    bool get_codepoint_bulk(std::true_type /*bulk*/, int& out)
+    {
+        if (next_unget || ia.bulk_remaining() < 4)
+        {
+            return false;
+        }
+        const char_type* const raw = ia.bulk_data();
+        const int codepoint = hex_codepoint(reinterpret_cast<const unsigned char*>(raw));
+        if (codepoint < 0)
+        {
+            return false;
+        }
+        ia.bulk_skip(4);
+        // a hex digit is never a newline, so only the flat counters advance
+        position.chars_read_total += 4;
+        position.chars_read_current_line += 4;
+        current = char_traits<char_type>::to_int_type(raw[3]);
+        out = codepoint;
+        return true;
+    }
+
+    /// streaming input: no bulk fast path
+    bool get_codepoint_bulk(std::false_type /*bulk*/, int& /*out*/) const noexcept
+    {
+        return false;
+    }
+
    /*!
    @brief get codepoint from 4 hex characters following `\\u`

@@ -240,6 +278,14 @@ class lexer : public lexer_base<BasicJsonType>
    {
        // this function only makes sense after reading `\u`
        JSON_ASSERT(current == 'u');
+
+        // contiguous input: decode all 4 hex digits directly from the buffer
+        int fast_codepoint = 0;
+        if (get_codepoint_bulk(std::integral_constant<bool, bulk_scan> {}, fast_codepoint))
+        {
+            return fast_codepoint;
+        }
+
        int codepoint = 0;

        const auto factors = { 12u, 8u, 4u, 0u };
@@ -1044,9 +1090,11 @@ class lexer : public lexer_base<BasicJsonType>
            token_type::parse_error otherwise

    @note The scanner is independent of the current locale: token_buffer
-          always holds `.`. Only the std::strtod fallback of convert_number()
-          depends on the locale, and it looks up the decimal point right
-          before converting (see detail::convert_float_locale_aware()).
+          always holds `.`. The conversion of float and double does not use
+          the locale either. Only the std::strtold fallback of
+          convert_number() for long double formats other than binary64
+          depends on it, and it looks up the decimal point right before
+          converting (see detail::convert_float_locale_aware()).
    */
    token_type scan_number()  // lgtm [cpp/use-of-goto] `goto` is used in this function to implement the number-parsing state machine described above. By design, any finite input will eventually reach the "done" state or return token_type::parse_error. In each intermediate state, 1 byte of the input is appended to the token_buffer vector, and only the already initialized variables token_buffer, number_type, and error_message are manipulated.
    {
@@ -1059,7 +1107,7 @@ class lexer : public lexer_base<BasicJsonType>

        // offset just past the last mantissa byte in token_buffer (i.e. the
        // index of 'e'/'E', or the whole token when there is no exponent).
-        // convert_number() uses it to count significant digits; npos means
+        // convert_number() uses it to split the token; npos means
        // "not seen an exponent yet" and is resolved at scan_number_done
        std::size_t mantissa_end = std::string::npos;

@@ -1389,8 +1437,8 @@ scan_number_done:
    @param[in] mantissa_end  offset just past the last mantissa byte in
                             token_buffer (the index of 'e'/'E', or
                             token_buffer.size() when there is no exponent);
-                             used to skip Clinger's fast path when it cannot
-                             possibly succeed - see detail::mantissa_fits_clinger()
+                             with decimal_point_position, it locates the parts
+                             of a float token without scanning it again
    */
    token_type convert_number(token_type number_type, std::size_t mantissa_end)
    {
@@ -1444,10 +1492,11 @@ scan_number_done:
        }

        // this code is reached if we parse a floating-point number or if an
-        // integer conversion above overflowed. Prefer std::from_chars
-        // (Eisel-Lemire, locale-independent, correctly rounded) when available;
-        // otherwise the exact Clinger fast path (double only); otherwise the
-        // locale-aware strtof/strtod/strtold.
+        // integer conversion above overflowed. float and double (and long
+        // double where it is binary64) are converted by the library itself,
+        // correctly rounded and independent of the locale; other long double
+        // formats use std::from_chars when available, otherwise the
+        // locale-aware strtold.
        if (convert_float_fast(num_begin, num_end, decimal_point_position, mantissa_end, value_float))
        {
            return token_type::value_float;
@@ -2021,6 +2070,39 @@ scan_number_done:
        // read the next character and ignore whitespace
        skip_whitespace();

+        return scan_after_whitespace();
+    }
+
+    /*!
+    @brief scan the next token when the caller expects a separator (':' or
+           ',') most of the time
+
+    After an object key the next token is almost always ':', after a value
+    inside an object or array almost always ','. Testing for that character
+    first is a compare and a well-predicted branch, where the switch in
+    scan_after_whitespace() is an indirect jump through a table. Anything else
+    goes through the switch, so the result is the same as scan()'s.
+
+    May only be called after scan() has run once (the BOM check is skipped).
+    */
+    token_type scan_expecting(token_type expected_type)
+    {
+        JSON_ASSERT(expected_type == token_type::name_separator || expected_type == token_type::value_separator);
+        JSON_ASSERT(position.chars_read_total > 0);
+        const char_int_type expected_char = static_cast<unsigned char>((expected_type == token_type::name_separator) ? ':' : ',');
+        skip_whitespace();
+        if (JSON_HEDLEY_LIKELY(current == expected_char))
+        {
+            return expected_type;
+        }
+        return scan_after_whitespace();
+    }
+
+  private:
+    /// the part of scan() after the leading whitespace: skip comments and
+    /// scan the token that starts with current
+    token_type scan_after_whitespace()
+    {
        // ignore comments
        while (ignore_comments && current == '/')
        {
@@ -2100,7 +2182,6 @@ scan_number_done:
        }
    }

-  private:
    /// input adapter
    InputAdapterType ia;

@@ -260,7 +260,7 @@ class parser
                        }

                        // parse separator (:)
-                        if (JSON_HEDLEY_UNLIKELY(get_token() != token_type::name_separator))
+                        if (JSON_HEDLEY_UNLIKELY(!get_token_expecting(token_type::name_separator)))
                        {
                            return sax->parse_error(m_lexer.get_position(),
                                                    m_lexer.get_token_string(),
@@ -423,7 +423,7 @@ class parser
            {
                // comma -> next value
                // or end of array (ignore_trailing_commas = true)
-                if (get_token() == token_type::value_separator)
+                if (get_token_expecting(token_type::value_separator))
                {
                    // parse a new value
                    get_token();
@@ -463,7 +463,7 @@ class parser

            // comma -> next value
            // or end of object (ignore_trailing_commas = true)
-            if (get_token() == token_type::value_separator)
+            if (get_token_expecting(token_type::value_separator))
            {
                get_token();

@@ -484,7 +484,7 @@ class parser
                    }

                    // parse separator (:)
-                    if (JSON_HEDLEY_UNLIKELY(get_token() != token_type::name_separator))
+                    if (JSON_HEDLEY_UNLIKELY(!get_token_expecting(token_type::name_separator)))
                    {
                        return sax->parse_error(m_lexer.get_position(),
                                                m_lexer.get_token_string(),
@@ -528,6 +528,13 @@ class parser
        return last_token = m_lexer.scan();
    }

+    /// get next token from lexer; true if it is the separator @a expected_type
+    /// (name_separator or value_separator), which it usually is
+    bool get_token_expecting(token_type expected_type)
+    {
+        return (last_token = m_lexer.scan_expecting(expected_type)) == expected_type;
+    }
+
    std::string exception_message(const token_type expected, const std::string& context)
    {
        std::string error_msg = "syntax error ";
@@ -8,10 +8,12 @@

 #pragma once

+#include <array> // array
 #include <cstddef> // size_t
-#include <cstdint> // uint64_t
+#include <cstdint> // uint64_t, uint8_t
 #include <cstring> // memcpy

+#include <nlohmann/detail/bit_ops.hpp>
 #include <nlohmann/detail/macro_scope.hpp>

 // Optional SIMD backend for bulk UTF-8 validation. This is an opt-in external
@@ -69,18 +71,12 @@ inline std::size_t find_string_special(const unsigned char* data, std::size_t n)
    std::size_t i = 0;
    for (; i + 8 <= n; i += 8)
    {
-        std::uint64_t word = 0;
-        std::memcpy(&word, data + i, sizeof(word));
-        if (swar_string_special(word) != 0)
+        const std::uint64_t special = swar_string_special(read_eight_bytes(data + i));
+        if (special != 0)
        {
-            // a special byte is in this word; locate it (endian-agnostic)
-            for (std::size_t j = 0; j < 8; ++j)
-            {
-                if (is_string_special(data[i + j]))
-                {
-                    return i + j;
-                }
-            }
+            // the lowest flagged byte is the first special one: the borrows of
+            // the subtractions can only flag bytes above a true hit
+            return i + (static_cast<std::size_t>(count_trailing_zeros(special)) / 8);
        }
    }
    for (; i < n; ++i)
@@ -114,8 +110,7 @@ inline std::size_t find_ascii_copyable_run(const unsigned char* data, std::size_
    std::size_t i = 0;
    for (; i + 8 <= n; i += 8)
    {
-        std::uint64_t v = 0;
-        std::memcpy(&v, data + i, sizeof(v));
+        const std::uint64_t v = read_eight_bytes(data + i);
        const std::uint64_t q = v ^ 0x2222222222222222ull; // '"'  (0x22)
        const std::uint64_t b = v ^ 0x5C5C5C5C5C5C5C5Cull; // '\\' (0x5C)
        const std::uint64_t d = v ^ 0x7F7F7F7F7F7F7F7Full; // DEL  (0x7F)
@@ -126,7 +121,9 @@ inline std::size_t find_ascii_copyable_run(const unsigned char* data, std::size_
                                   | (v & high);               // >= 0x80
        if (stop != 0)
        {
-            break;
+            // the lowest flagged byte is the first one to stop at (see
+            // find_string_special())
+            return i + (static_cast<std::size_t>(count_trailing_zeros(stop)) / 8);
        }
    }
    for (; i < n; ++i)
@@ -253,12 +250,18 @@ inline std::size_t scalar_string_bulk_run(const unsigned char* data, std::size_t
        {
            break; // end of buffer, or a quote/escape/control byte
        }
-        const std::size_t seq = validate_one_utf8(data + pos, n - pos);
-        if (seq == 0)
+        // a run of multi-byte sequences (e.g. CJK text) is validated sequence
+        // by sequence without searching for the next special byte in between
+        do
        {
-            break; // ill-formed or truncated: let the byte path diagnose it
+            const std::size_t seq = validate_one_utf8(data + pos, n - pos);
+            if (seq == 0)
+            {
+                return pos; // ill-formed or truncated: let the byte path diagnose it
+            }
+            pos += seq;
        }
-        pos += seq;
+        while (pos < n && data[pos] >= 0x80u);
    }
    return pos;
 }
@@ -273,8 +276,7 @@ inline std::size_t find_string_delimiter(const unsigned char* data, std::size_t
    std::size_t i = 0;
    for (; i + 8 <= n; i += 8)
    {
-        std::uint64_t v = 0;
-        std::memcpy(&v, data + i, sizeof(v));
+        const std::uint64_t v = read_eight_bytes(data + i);
        const std::uint64_t q = v ^ 0x2222222222222222ull;
        const std::uint64_t b = v ^ 0x5C5C5C5C5C5C5C5Cull;
        const std::uint64_t hit = ((q - ones) & ~q & high)
@@ -282,14 +284,8 @@ inline std::size_t find_string_delimiter(const unsigned char* data, std::size_t
                                  | ((v - 0x2020202020202020ull) & ~v & high);
        if (hit != 0)
        {
-            for (std::size_t j = 0; j < 8; ++j)
-            {
-                const unsigned char c = data[i + j];
-                if (c == '\"' || c == '\\' || c < 0x20u)
-                {
-                    return i + j;
-                }
-            }
+            // the lowest flagged byte is the first delimiter (see find_string_special())
+            return i + (static_cast<std::size_t>(count_trailing_zeros(hit)) / 8);
        }
    }
    for (; i < n; ++i)
@@ -320,5 +316,50 @@ inline std::size_t string_bulk_run(const unsigned char* data, std::size_t n) noe
    return scalar_string_bulk_run(data, n);
 }

+// Decode the 4 hex digits at [data, data+4) - the digits following a `\u`
+// escape - into a codepoint 0x0000..0xFFFF via one table lookup per byte
+// (after yyjson's read_hex_u16), or return -1 if any of the 4 bytes is not a
+// hex digit ('0'..'9', 'A'..'F', 'a'..'f'). The caller must already have
+// checked that 4 bytes are available; used by lexer::get_codepoint()'s
+// contiguous fast path. On -1 it falls back to the byte-at-a-time loop, which
+// stops at the first invalid digit, so the reported error and position are
+// unaffected by this fast path.
+inline int hex_codepoint(const unsigned char* data) noexcept
+{
+    static const std::array<std::uint8_t, 256> hex_digit_table = // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)
+    {
+        {
+            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 00..0F
+            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 10..1F
+            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 20..2F
+            0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 30..3F ('0'..'9')
+            0xFF, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 40..4F ('A'..'F')
+            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 50..5F
+            0xFF, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 60..6F ('a'..'f')
+            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 70..7F
+            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 80..8F
+            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 90..9F
+            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // A0..AF
+            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // B0..BF
+            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // C0..CF
+            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // D0..DF
+            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // E0..EF
+            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF  // F0..FF
+        }
+    };
+
+    const std::uint8_t d0 = hex_digit_table[data[0]];
+    const std::uint8_t d1 = hex_digit_table[data[1]];
+    const std::uint8_t d2 = hex_digit_table[data[2]];
+    const std::uint8_t d3 = hex_digit_table[data[3]];
+    // every valid digit is <= 0xF; the combined OR only exceeds it if at
+    // least one of the four bytes was not a hex digit (looked up as 0xFF)
+    if ((d0 | d1 | d2 | d3) > 0x0F)
+    {
+        return -1;
+    }
+    return (d0 << 12) | (d1 << 8) | (d2 << 4) | d3;
+}
+
 }  // namespace detail
 NLOHMANN_JSON_NAMESPACE_END
@@ -81,9 +81,13 @@ class json_pointer
    /// @sa https://json.nlohmann.me/api/json_pointer/operator_string_t/
    JSON_HEDLEY_DEPRECATED_FOR(3.11.0, to_string())
    operator string_t() const
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+        = delete;
+#else
    {
        return to_string();
    }
+#endif

 #ifndef JSON_NO_IO
    /// @brief write string representation of the JSON pointer to stream
@@ -1022,9 +1026,13 @@ class json_pointer
    /// @sa https://json.nlohmann.me/api/json_pointer/operator_eq/
    JSON_HEDLEY_DEPRECATED_FOR(3.11.2, operator==(json_pointer))
    bool operator==(const string_t& rhs) const
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+        = delete;
+#else
    {
        return *this == json_pointer(rhs);
    }
+#endif

    /// @brief 3-way compares two JSON pointers
    template<typename RefStringTypeRhs>
@@ -1102,18 +1110,26 @@ template<typename RefStringTypeLhs,
 JSON_HEDLEY_DEPRECATED_FOR(3.11.2, operator==(json_pointer, json_pointer))
 inline bool operator==(const json_pointer<RefStringTypeLhs>& lhs,
                       const StringType& rhs)
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+    = delete;
+#else
 {
    return lhs == json_pointer<RefStringTypeLhs>(rhs);
 }
+#endif

 template<typename RefStringTypeRhs,
         typename StringType = typename json_pointer<RefStringTypeRhs>::string_t>
 JSON_HEDLEY_DEPRECATED_FOR(3.11.2, operator==(json_pointer, json_pointer))
 inline bool operator==(const StringType& lhs,
                       const json_pointer<RefStringTypeRhs>& rhs)
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+    = delete;
+#else
 {
    return json_pointer<RefStringTypeRhs>(lhs) == rhs;
 }
+#endif

 template<typename RefStringTypeLhs, typename RefStringTypeRhs>
 inline bool operator!=(const json_pointer<RefStringTypeLhs>& lhs,
@@ -1127,18 +1143,26 @@ template<typename RefStringTypeLhs,
 JSON_HEDLEY_DEPRECATED_FOR(3.11.2, operator!=(json_pointer, json_pointer))
 inline bool operator!=(const json_pointer<RefStringTypeLhs>& lhs,
                       const StringType& rhs)
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+    = delete;
+#else
 {
    return !(lhs == rhs);
 }
+#endif

 template<typename RefStringTypeRhs,
         typename StringType = typename json_pointer<RefStringTypeRhs>::string_t>
 JSON_HEDLEY_DEPRECATED_FOR(3.11.2, operator!=(json_pointer, json_pointer))
 inline bool operator!=(const StringType& lhs,
                       const json_pointer<RefStringTypeRhs>& rhs)
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+    = delete;
+#else
 {
    return !(lhs == rhs);
 }
+#endif

 template<typename RefStringTypeLhs, typename RefStringTypeRhs>
 inline bool operator<(const json_pointer<RefStringTypeLhs>& lhs,
@@ -888,6 +888,10 @@
    #define JSON_DISABLE_ENUM_SERIALIZATION 0
 #endif

+#ifndef JSON_DELETE_DEPRECATED_FUNCTIONS
+    #define JSON_DELETE_DEPRECATED_FUNCTIONS 0
+#endif
+
 #ifndef JSON_DISABLE_TUPLE_REFERENCE_CONVERSION
    #define JSON_DISABLE_TUPLE_REFERENCE_CONVERSION 0
 #endif
@@ -21,6 +21,8 @@
 #undef JSON_NO_UNIQUE_ADDRESS
 #undef JSON_DISABLE_ENUM_SERIALIZATION
 #undef JSON_DISABLE_TUPLE_REFERENCE_CONVERSION
+#undef JSON_DTOA_SSE2
+#undef JSON_DTOA_NEON

 #ifndef JSON_TEST_KEEP_MACROS
    #undef JSON_CATCH
@@ -43,6 +45,8 @@
    #undef JSON_PRECISE_STREAM_POSITION
    #undef JSON_STRICT_NUL_HANDLING
    #undef JSON_STRICT_BINARY_UTF8
+    #undef JSON_DELETE_DEPRECATED_FUNCTIONS
+    #undef JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
 #endif

 #include <nlohmann/thirdparty/hedley/hedley_undef.hpp>
@@ -438,6 +438,30 @@ template<typename BasicJsonType, typename CompatibleObjectType>
 struct is_compatible_object_type
    : is_compatible_object_type_impl<BasicJsonType, CompatibleObjectType> {};

+template<typename T>
+using insert_result_t = decltype(std::declval<T&>().insert(std::declval<const value_type_t<T>&>()));
+
+template<typename T>
+using insert_result_second_t = decltype(std::declval<T&>().insert(std::declval<const value_type_t<T>&>()).second);
+
+// a map-like type (std::map, std::unordered_map, ...) whose keys are enums; see
+// JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
+template<typename T, typename = void>
+struct is_enum_keyed_map : std::false_type {};
+
+template<typename T>
+struct is_enum_keyed_map <
+    T, enable_if_t < is_detected<mapped_type_t, T>::value&&
+    is_detected<key_type_t, T>::value >>
+{
+    // maps with non-unique keys (std::multimap, std::unordered_multimap, ...)
+    // are excluded, because an object cannot hold duplicate keys; they are
+    // detected by insert() returning an iterator instead of a pair<iterator, bool>
+    // NOLINTNEXTLINE(modernize-type-traits) we use C++11
+    static constexpr bool value = std::is_enum<typename T::key_type>::value &&
+                                  !(is_detected<insert_result_t, T>::value && !is_detected<insert_result_second_t, T>::value);
+};
+
 template<typename BasicJsonType, typename ConstructibleObjectType,
         typename = void>
 struct is_constructible_object_type_impl : std::false_type {};
@@ -882,6 +906,21 @@ T conditional_static_cast(U value)
    return value;
 }

+// like conditional_static_cast, but converts to bool by comparing with zero,
+// because MSVC 2015 warns about any conversion to bool (C4800), even with an
+// explicit cast; used for enums whose underlying type is bool
+template < typename T, typename U, enable_if_t < !std::is_same<T, bool>::value, int > = 0 >
+T bool_aware_static_cast(U value)
+{
+    return conditional_static_cast<T>(value);
+}
+
+template<typename T, typename U, enable_if_t<std::is_same<T, bool>::value, int> = 0>
+bool bool_aware_static_cast(U value)
+{
+    return value != U();
+}
+
 template<typename... Types>
 using all_integral = conjunction<std::is_integral<Types>...>;

@@ -127,6 +127,7 @@ class binary_writer
    @throw type_error.316 if a string value or an object key is not valid
           UTF-8
    @throw type_error.317 if @a j is not an object
+    @throw type_error.321 if a value nested in @a j is discarded
    */
    void write_bson(const BasicJsonType& j)
    {
@@ -158,6 +159,7 @@ class binary_writer
    @param[in] j  JSON value to serialize
    @throw type_error.316 if a string value or an object key is not valid
           UTF-8
+    @throw type_error.321 if @a j or a value nested in it is discarded
    */
    void write_cbor(const BasicJsonType& j)
    {
@@ -322,7 +324,7 @@ class binary_writer

            case value_t::discarded:
            default:
-                break;
+                throw_on_discarded(j, "CBOR");
        }
    }

@@ -382,6 +384,7 @@ class binary_writer

    /*!
    @param[in] j  JSON value to serialize
+    @throw type_error.321 if @a j or a value nested in it is discarded
    */
    void write_msgpack(const BasicJsonType& j)
    {
@@ -655,7 +658,7 @@ class binary_writer

            case value_t::discarded:
            default:
-                break;
+                throw_on_discarded(j, "MessagePack");
        }
    }

@@ -668,6 +671,7 @@ class binary_writer
    @param[in] bjdata_version  which BJData version to use, default is draft2
    @throw type_error.316 if a string value or an object key is not valid
           UTF-8
+    @throw type_error.321 if @a j or a value nested in it is discarded
    */
    void write_ubjson(const BasicJsonType& j, const bool use_count,
                      const bool use_type, const bool add_prefix = true,
@@ -901,7 +905,7 @@ class binary_writer

            case value_t::discarded:
            default:
-                break;
+                throw_on_discarded(j, use_bjdata ? "BJData" : "UBJSON");
        }
    }

@@ -921,6 +925,15 @@ class binary_writer
    }

  private:
+    /*!
+    @brief throws because @a j is discarded and cannot be serialized
+    @throw type_error.321 always
+    */
+    JSON_HEDLEY_NO_RETURN static void throw_on_discarded(const BasicJsonType& j, const char* format_name)
+    {
+        JSON_THROW(type_error::create(321, concat("cannot serialize discarded value to ", format_name), &j));
+    }
+
    //////////
    // BSON //
    //////////
@@ -1172,6 +1185,7 @@ class binary_writer
           into a byte, before anything is written
    @throw type_error.316 if @a j is a string that is not valid UTF-8, before
           anything is written
+    @throw type_error.321 if @a j is discarded
    */
    std::size_t calc_bson_value_size(const BasicJsonType& j)
    {
@@ -1198,10 +1212,12 @@ class binary_writer
            case value_t::null:
                return 0ul;

+            case value_t::discarded:
+                throw_on_discarded(j, "BSON");
+
            // LCOV_EXCL_START
            case value_t::object:
            case value_t::array:
-            case value_t::discarded:
            default:
                JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert)
                return 0ul;
@@ -1238,10 +1254,12 @@ class binary_writer
            case value_t::null:
                return write_bson_null(name);

+            case value_t::discarded:
+                throw_on_discarded(j, "BSON");
+
            // LCOV_EXCL_START
            case value_t::object:
            case value_t::array:
-            case value_t::discarded:
            default:
                JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert)
                return;
@@ -1308,6 +1326,8 @@ class binary_writer
           byte, before anything is written
    @throw type_error.316 if a string value or a key is not valid UTF-8,
           before anything is written
+    @throw type_error.321 if a value nested in @a document is discarded,
+           before anything is written
    */
    std::size_t calc_bson_sizes(const BasicJsonType& document, std::vector<std::size_t>& nested_sizes)
    {
@@ -1366,8 +1366,9 @@ class serializer
    /*!
    @brief dump an integer

-    Dump a given integer, appending it to @ref write_buffer. Works internally with
-    @a number_buffer.
+    Dump a given integer, appending it to @ref write_buffer (directly: copying
+    the digits from another buffer right after writing them waits until the
+    stores are done).

    @param[in] x  integer number (signed or unsigned) to dump
    @tparam NumberType either @a number_integer_t or @a number_unsigned_t
@@ -1402,33 +1403,57 @@ class serializer
            return;
        }

-        // use a pointer to fill the buffer
-        auto buffer_ptr = number_buffer.begin(); // NOLINT(llvm-qualified-auto,readability-qualified-auto)
+        // use a pointer to fill the buffer (room for as much as number_buffer holds)
+        if (JSON_HEDLEY_UNLIKELY(write_buffer_pos + number_buffer.size() > write_buffer.size()))
+        {
+            flush();
+        }
+        auto* buffer_ptr = write_buffer.data() + write_buffer_pos;

        number_unsigned_t abs_value;

-        unsigned int n_chars{};
+        // one byte for the minus sign
+        unsigned int n_chars = 0;

        if (is_negative_number(x))
        {
            *buffer_ptr = '-';
            abs_value = remove_sign(static_cast<number_integer_t>(x));
-
-            // account one more byte for the minus sign
-            n_chars = 1 + count_digits(abs_value);
+            n_chars = 1;
        }
        else
        {
            abs_value = static_cast<number_unsigned_t>(x);
-            n_chars = count_digits(abs_value);
        }

+        // up to 16 digits: eight at a time (as the digits of floats), written
+        // without leading zeros
+        if (abs_value < 10000000000000000u)
+        {
+            const std::uint64_t value = abs_value;
+            const std::uint64_t upper = value / 100000000u;
+            const std::uint64_t first = dtoa_impl::eight_digit_bytes(upper != 0 ? upper : value);
+            const auto leading = static_cast<unsigned>(count_leading_zeros(first) / 8); // (first is not 0)
+            char* const p = buffer_ptr + n_chars;
+            dtoa_impl::store_msb_first(p, (first << (8 * leading)) + 0x3030303030303030u);
+            n_chars += 8 - leading;
+            if (upper != 0)
+            {
+                dtoa_impl::store_msb_first(p + 8 - leading, dtoa_impl::eight_digit_bytes(value - (upper * 100000000u)) + 0x3030303030303030u);
+                n_chars += 8;
+            }
+            write_buffer_pos += n_chars;
+            return;
+        }
+
+        n_chars += count_digits(abs_value);
+
        // spare 1 byte for '\0'
        JSON_ASSERT(n_chars < number_buffer.size() - 1);

        // jump to the end to generate the string from backward,
        // so we later avoid reversing the result
-        buffer_ptr += static_cast<typename decltype(number_buffer)::difference_type>(n_chars);
+        buffer_ptr += n_chars;

        // Fast int2ascii implementation inspired by "Fastware" talk by Andrei Alexandrescu
        // See: https://www.youtube.com/watch?v=o4-CwDo2zpg
@@ -1451,14 +1476,13 @@ class serializer
            *(--buffer_ptr) = static_cast<char>('0' + abs_value);
        }

-        put_buffer(number_buffer, n_chars);
+        write_buffer_pos += n_chars;
    }

    /*!
    @brief dump a floating-point number

-    Dump a given floating-point number, appending it to @ref write_buffer. Works internally
-    with @a number_buffer.
+    Dump a given floating-point number, appending it to @ref write_buffer.

    @param[in] x  floating-point number to dump
    */
@@ -1485,10 +1509,15 @@ class serializer

    void dump_float(number_float_t x, std::true_type /*is_ieee_single_or_double*/)
    {
-        auto* begin = number_buffer.data();
+        // directly into the write buffer: copying the text from number_buffer
+        // right after to_chars() wrote it waits until its stores are done
+        if (JSON_HEDLEY_UNLIKELY(write_buffer_pos + number_buffer.size() > write_buffer.size()))
+        {
+            flush();
+        }
+        auto* begin = write_buffer.data() + write_buffer_pos;
        auto* end = ::nlohmann::detail::to_chars(begin, begin + number_buffer.size(), x);
-
-        put_buffer(number_buffer, static_cast<std::size_t>(end - begin));
+        write_buffer_pos += static_cast<std::size_t>(end - begin);
    }

    JSON_HEDLEY_NON_NULL(1)
@@ -612,100 +612,210 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
        /// constructor for rvalue binary arrays (internal type)
        json_value(binary_t&& value) : binary(create<binary_t>(std::move(value))) {}

-        void destroy(value_t t)
+private:
+        // raw, allocation-free transfer of m_data from src to dst: no
+        // set_parents()/assert_invariant() (the former is O(#children) per
+        // call under JSON_DIAGNOSTICS, which would make the walk below
+        // quadratic); dst takes ownership, src is left as value_t::null.
+        static void take(basic_json& dst, basic_json& src) noexcept
+        {
+            dst.m_data.m_type = src.m_data.m_type;
+            dst.m_data.m_value = src.m_data.m_value;
+            src.m_data.m_type = value_t::null;
+        }
+
+        // true if v is not an array/object, or is an already-empty one
+        static bool has_no_children(const basic_json& v) noexcept
+        {
+            switch (v.m_data.m_type)
+            {
+                case value_t::array:
+                    return v.m_data.m_value.array->empty();
+                case value_t::object:
+                    return v.m_data.m_value.object->empty();
+                default:
+                    return true;
+            }
+        }
+
+        static basic_json& last_child(basic_json& v)
+        {
+            if (v.m_data.m_type == value_t::array)
+            {
+                return v.m_data.m_value.array->back();
+            }
+            JSON_ASSERT(v.m_data.m_type == value_t::object);
+            return v.m_data.m_value.object->rbegin()->second;
+        }
+
+        // removes the last child of a non-empty array/object v; this never
+        // allocates, and since it is only ever called when that child is a
+        // scalar or an already-empty array/object, destroying it never
+        // recurses more than one level deep (see destroy() below)
+        static void pop_last_child(basic_json& v)
+        {
+            if (v.m_data.m_type == value_t::array)
+            {
+                v.m_data.m_value.array->pop_back();
+            }
+            else
+            {
+                JSON_ASSERT(v.m_data.m_type == value_t::object);
+                // erase() needs a forward iterator, so std::prev(end()) is
+                // used here rather than rbegin() (see last_child() above)
+                v.m_data.m_value.object->erase(std::prev(v.m_data.m_value.object->end()));
+            }
+        }
+
+        // deallocates the (already empty) array/object held by v; this is
+        // the same allocator-based free the old recursive implementation
+        // used, just factored out so every level of the walk in destroy()
+        // can share it
+        static void free_container(basic_json& v) noexcept
+        {
+            if (v.m_data.m_type == value_t::array)
+            {
+                JSON_ASSERT(v.m_data.m_value.array->empty());
+                AllocatorType<array_t> alloc;
+                std::allocator_traits<decltype(alloc)>::destroy(alloc, v.m_data.m_value.array);
+                std::allocator_traits<decltype(alloc)>::deallocate(alloc, v.m_data.m_value.array, 1);
+            }
+            else
+            {
+                JSON_ASSERT(v.m_data.m_type == value_t::object);
+                JSON_ASSERT(v.m_data.m_value.object->empty());
+                AllocatorType<object_t> alloc;
+                std::allocator_traits<decltype(alloc)>::destroy(alloc, v.m_data.m_value.object);
+                std::allocator_traits<decltype(alloc)>::deallocate(alloc, v.m_data.m_value.object, 1);
+            }
+            v.m_data.m_type = value_t::null; // avoid a double free if v is later destructed
+        }
+
+public:
+        void destroy_string() noexcept
+        {
+            if (string == nullptr)
+            {
+                // not initialized (e.g., due to exception in the ctor)
+                return;
+            }
+            AllocatorType<string_t> alloc;
+            std::allocator_traits<decltype(alloc)>::destroy(alloc, string);
+            std::allocator_traits<decltype(alloc)>::deallocate(alloc, string, 1);
+        }
+
+        void destroy_binary() noexcept
+        {
+            if (binary == nullptr)
+            {
+                // not initialized (e.g., due to exception in the ctor)
+                return;
+            }
+            AllocatorType<binary_t> alloc;
+            std::allocator_traits<decltype(alloc)>::destroy(alloc, binary);
+            std::allocator_traits<decltype(alloc)>::deallocate(alloc, binary, 1);
+        }
+
+        // t must be value_t::array or value_t::object
+        void destroy_container(value_t t) noexcept
        {
            if (
                (t == value_t::object && object == nullptr) ||
-                (t == value_t::array && array == nullptr) ||
-                (t == value_t::string && string == nullptr) ||
-                (t == value_t::binary && binary == nullptr)
+                (t == value_t::array && array == nullptr)
            )
            {
                // not initialized (e.g., due to exception in the ctor)
                return;
            }
-            if (t == value_t::array || t == value_t::object)
+
+            // Destroy the tree without recursing per nesting level and
+            // without any heap allocation: a heap-allocated flattening
+            // stack (the previous implementation) can itself throw
+            // bad_alloc, which would escape this noexcept destructor and
+            // terminate the program (#5135).
+            //
+            // Instead, walk down the "last child" chain, reversing links
+            // as we go: cur is the container currently being emptied,
+            // and prev is its parent (value_t::null when there is none).
+            // Each parent's last child slot doubles as storage for that
+            // parent's own parent link while we are below it, so no
+            // extra memory is needed. We only ever remove a child once
+            // it is a scalar or an empty array/object, which neither
+            // allocates nor recurses more than one level deep.
+            //
+            // This json_value is not itself a basic_json, so the
+            // top-level container is first moved into a local stand-in
+            // ("cur"); a default-constructed basic_json has a null
+            // pointer in its m_value (see data::m_value's initializer),
+            // so swapping it with *this leaves this union's own pointer
+            // null, and it is never looked at or freed a second time.
+            basic_json cur;
+            cur.m_data.m_type = t;
+            using std::swap;
+            swap(cur.m_data.m_value, *this);
+
+            basic_json prev; // value_t::null: no parent
+
+            while (true)
            {
-                // flatten the current json_value to a heap-allocated stack
-                std::vector<basic_json> stack;
-
-                // move the top-level items to stack
-                if (t == value_t::array)
+                if (has_no_children(cur))
                {
-                    stack.reserve(array->size());
-                    std::move(array->begin(), array->end(), std::back_inserter(stack));
-                }
-                else
-                {
-                    stack.reserve(object->size());
-                    for (auto&& it : *object)
+                    if (prev.m_data.m_type == value_t::null)
                    {
-                        stack.push_back(std::move(it.second));
-                    }
-                }
-
-                while (!stack.empty())
-                {
-                    // move the last item to a local variable to be processed
-                    basic_json current_item(std::move(stack.back()));
-                    stack.pop_back();
-
-                    // if current_item is array/object, move
-                    // its children to the stack to be processed later
-                    if (current_item.is_array())
-                    {
-                        std::move(current_item.m_data.m_value.array->begin(), current_item.m_data.m_value.array->end(), std::back_inserter(stack));
-
-                        current_item.m_data.m_value.array->clear();
-                    }
-                    else if (current_item.is_object())
-                    {
-                        for (auto&& it : *current_item.m_data.m_value.object)
-                        {
-                            stack.push_back(std::move(it.second));
-                        }
-
-                        current_item.m_data.m_value.object->clear();
+                        free_container(cur);
+                        return; // back at the top with nothing left to do
                    }

-                    // it's now safe that current_item gets destructed
-                    // since it doesn't have any children
+                    // ascend: detach the grandparent link from prev's
+                    // last slot, drop that (now null) slot, free cur
+                    // (it is empty), then move up one level
+                    basic_json gp;
+                    take(gp, last_child(prev));
+                    pop_last_child(prev);
+
+                    free_container(cur);
+
+                    take(cur, prev);
+                    take(prev, gp);
+                    continue;
                }
+
+                basic_json& cur_last_ref = last_child(cur);
+
+                if (has_no_children(cur_last_ref))
+                {
+                    // scalar, or already-empty array/object
+                    pop_last_child(cur);
+                    continue;
+                }
+
+                // descend into the non-empty last child, reversing the
+                // link: its slot takes over prev, and the child becomes
+                // the new cur
+                basic_json tmp;
+                take(tmp, cur_last_ref);
+                take(cur_last_ref, prev);
+                take(prev, cur);
+                take(cur, tmp);
            }
+        }

+        void destroy(value_t t)
+        {
            switch (t)
            {
-                case value_t::object:
-                {
-                    AllocatorType<object_t> alloc;
-                    std::allocator_traits<decltype(alloc)>::destroy(alloc, object);
-                    std::allocator_traits<decltype(alloc)>::deallocate(alloc, object, 1);
-                    break;
-                }
-
-                case value_t::array:
-                {
-                    AllocatorType<array_t> alloc;
-                    std::allocator_traits<decltype(alloc)>::destroy(alloc, array);
-                    std::allocator_traits<decltype(alloc)>::deallocate(alloc, array, 1);
-                    break;
-                }
-
                case value_t::string:
-                {
-                    AllocatorType<string_t> alloc;
-                    std::allocator_traits<decltype(alloc)>::destroy(alloc, string);
-                    std::allocator_traits<decltype(alloc)>::deallocate(alloc, string, 1);
+                    destroy_string();
                    break;
-                }

                case value_t::binary:
-                {
-                    AllocatorType<binary_t> alloc;
-                    std::allocator_traits<decltype(alloc)>::destroy(alloc, binary);
-                    std::allocator_traits<decltype(alloc)>::deallocate(alloc, binary, 1);
+                    destroy_binary();
+                    break;
+
+                case value_t::object:
+                case value_t::array:
+                    destroy_container(t);
                    break;
-                }

                case value_t::null:
                case value_t::boolean:
@@ -714,9 +824,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                case value_t::number_float:
                case value_t::discarded:
                default:
-                {
                    break;
-                }
            }
        }
    };
@@ -3492,9 +3600,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                   && !std::is_same<value_t, detail::uncvref_t<ValueType>>::value, int > = 0 >
    JSON_HEDLEY_DEPRECATED_FOR(3.11.0, basic_json::json_pointer or nlohmann::json_pointer<basic_json::string_t>) // NOLINT(readability/alt_tokens)
    ValueType value(const ::nlohmann::json_pointer<BasicJsonType>& ptr, const ValueType& default_value) const
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+    = delete;
+#else
    {
        return value(ptr.convert(), default_value);
    }
+#endif

    template < class ValueType, class BasicJsonType, class ReturnType = typename value_return_type<ValueType>::type,
               detail::enable_if_t <
@@ -3503,9 +3615,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                   && !std::is_same<value_t, detail::uncvref_t<ValueType>>::value, int > = 0 >
    JSON_HEDLEY_DEPRECATED_FOR(3.11.0, basic_json::json_pointer or nlohmann::json_pointer<basic_json::string_t>) // NOLINT(readability/alt_tokens)
    ReturnType value(const ::nlohmann::json_pointer<BasicJsonType>& ptr, ValueType && default_value) const
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+    = delete;
+#else
    {
        return value(ptr.convert(), std::forward<ValueType>(default_value));
    }
+#endif

    /// @brief access the first element
    /// @sa https://json.nlohmann.me/api/basic_json/front/
@@ -3863,9 +3979,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    JSON_HEDLEY_WARN_UNUSED_RESULT
    JSON_HEDLEY_DEPRECATED_FOR(3.11.0, basic_json::json_pointer or nlohmann::json_pointer<basic_json::string_t>) // NOLINT(readability/alt_tokens)
    bool contains(const typename ::nlohmann::json_pointer<BasicJsonType>& ptr) const
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+    = delete;
+#else
    {
        return ptr.contains(this);
    }
+#endif

    /// @}

@@ -3976,9 +4096,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    ///             that is, replace `json::iterator_wrapper(j)` with `j.items()`.
    JSON_HEDLEY_DEPRECATED_FOR(3.1.0, items())
    static iteration_proxy<iterator> iterator_wrapper(reference ref) noexcept
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+        = delete;
+#else
    {
        return ref.items();
    }
+#endif

    /// @brief wrapper to access iterator member functions in range-based for
    /// @sa https://json.nlohmann.me/api/basic_json/items/
@@ -3987,9 +4111,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    ///         that is, replace `json::iterator_wrapper(j)` with `j.items()`.
    JSON_HEDLEY_DEPRECATED_FOR(3.1.0, items())
    static iteration_proxy<const_iterator> iterator_wrapper(const_reference ref) noexcept
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+        = delete;
+#else
    {
        return ref.items();
    }
+#endif

    /// @brief helper to access iterator member functions in range-based for
    /// @sa https://json.nlohmann.me/api/basic_json/items/
@@ -5078,7 +5206,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    /// @sa https://json.nlohmann.me/api/basic_json/operator_le/
    template<typename ScalarType>
    requires std::is_scalar_v<ScalarType>
-    friend bool operator<=(ScalarType lhs, const_reference rhs) noexcept(std::is_nothrow_constructible<basic_json, ScalarType>::value)
+    friend bool operator<=(ScalarType lhs, const_reference rhs) noexcept(std::is_nothrow_constructible<detail::uncvref_t<decltype(rhs)>, ScalarType>::value)
    {
        return basic_json(lhs) <= rhs;
    }
@@ -5087,7 +5215,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    /// @sa https://json.nlohmann.me/api/basic_json/operator_ge/
    template<typename ScalarType>
    requires std::is_scalar_v<ScalarType>
-    friend bool operator>=(ScalarType lhs, const_reference rhs) noexcept(std::is_nothrow_constructible<basic_json, ScalarType>::value)
+    friend bool operator>=(ScalarType lhs, const_reference rhs) noexcept(std::is_nothrow_constructible<detail::uncvref_t<decltype(rhs)>, ScalarType>::value)
    {
        return basic_json(lhs) >= rhs;
    }
@@ -5108,11 +5236,16 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 #endif
    }

+    // The friend comparisons with a scalar name the JSON type via decltype of
+    // their parameter in noexcept, because older MSVC versions do not see the
+    // class scope there: MSVC 2015 and 2017 take basic_json as the template,
+    // and MSVC 2019 16.0 rejects member types and template parameters.
+
    /// @brief comparison: equal
    /// @sa https://json.nlohmann.me/api/basic_json/operator_eq/
    template<typename ScalarType, typename std::enable_if<
                 std::is_scalar<ScalarType>::value, int>::type = 0>
-    friend bool operator==(const_reference lhs, ScalarType rhs) noexcept(std::is_nothrow_constructible<basic_json, ScalarType>::value)
+    friend bool operator==(const_reference lhs, ScalarType rhs) noexcept(std::is_nothrow_constructible<detail::uncvref_t<decltype(lhs)>, ScalarType>::value)
    {
        return lhs == basic_json(rhs);
    }
@@ -5121,7 +5254,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    /// @sa https://json.nlohmann.me/api/basic_json/operator_eq/
    template<typename ScalarType, typename std::enable_if<
                 std::is_scalar<ScalarType>::value, int>::type = 0>
-    friend bool operator==(ScalarType lhs, const_reference rhs) noexcept(std::is_nothrow_constructible<basic_json, ScalarType>::value)
+    friend bool operator==(ScalarType lhs, const_reference rhs) noexcept(std::is_nothrow_constructible<detail::uncvref_t<decltype(rhs)>, ScalarType>::value)
    {
        return basic_json(lhs) == rhs;
    }
@@ -5137,7 +5270,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    /// @sa https://json.nlohmann.me/api/basic_json/operator_ne/
    template<typename ScalarType, typename std::enable_if<
                 std::is_scalar<ScalarType>::value, int>::type = 0>
-    friend bool operator!=(const_reference lhs, ScalarType rhs) noexcept(std::is_nothrow_constructible<basic_json, ScalarType>::value)
+    friend bool operator!=(const_reference lhs, ScalarType rhs) noexcept(std::is_nothrow_constructible<detail::uncvref_t<decltype(lhs)>, ScalarType>::value)
    {
        return lhs != basic_json(rhs);
    }
@@ -5146,7 +5279,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    /// @sa https://json.nlohmann.me/api/basic_json/operator_ne/
    template<typename ScalarType, typename std::enable_if<
                 std::is_scalar<ScalarType>::value, int>::type = 0>
-    friend bool operator!=(ScalarType lhs, const_reference rhs) noexcept(std::is_nothrow_constructible<basic_json, ScalarType>::value)
+    friend bool operator!=(ScalarType lhs, const_reference rhs) noexcept(std::is_nothrow_constructible<detail::uncvref_t<decltype(rhs)>, ScalarType>::value)
    {
        return basic_json(lhs) != rhs;
    }
@@ -5166,7 +5299,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    /// @sa https://json.nlohmann.me/api/basic_json/operator_lt/
    template<typename ScalarType, typename std::enable_if<
                 std::is_scalar<ScalarType>::value, int>::type = 0>
-    friend bool operator<(const_reference lhs, ScalarType rhs) noexcept(std::is_nothrow_constructible<basic_json, ScalarType>::value)
+    friend bool operator<(const_reference lhs, ScalarType rhs) noexcept(std::is_nothrow_constructible<detail::uncvref_t<decltype(lhs)>, ScalarType>::value)
    {
        return lhs < basic_json(rhs);
    }
@@ -5175,7 +5308,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    /// @sa https://json.nlohmann.me/api/basic_json/operator_lt/
    template<typename ScalarType, typename std::enable_if<
                 std::is_scalar<ScalarType>::value, int>::type = 0>
-    friend bool operator<(ScalarType lhs, const_reference rhs) noexcept(std::is_nothrow_constructible<basic_json, ScalarType>::value)
+    friend bool operator<(ScalarType lhs, const_reference rhs) noexcept(std::is_nothrow_constructible<detail::uncvref_t<decltype(rhs)>, ScalarType>::value)
    {
        return basic_json(lhs) < rhs;
    }
@@ -5195,7 +5328,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    /// @sa https://json.nlohmann.me/api/basic_json/operator_le/
    template<typename ScalarType, typename std::enable_if<
                 std::is_scalar<ScalarType>::value, int>::type = 0>
-    friend bool operator<=(const_reference lhs, ScalarType rhs) noexcept(std::is_nothrow_constructible<basic_json, ScalarType>::value)
+    friend bool operator<=(const_reference lhs, ScalarType rhs) noexcept(std::is_nothrow_constructible<detail::uncvref_t<decltype(lhs)>, ScalarType>::value)
    {
        return lhs <= basic_json(rhs);
    }
@@ -5204,7 +5337,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    /// @sa https://json.nlohmann.me/api/basic_json/operator_le/
    template<typename ScalarType, typename std::enable_if<
                 std::is_scalar<ScalarType>::value, int>::type = 0>
-    friend bool operator<=(ScalarType lhs, const_reference rhs) noexcept(std::is_nothrow_constructible<basic_json, ScalarType>::value)
+    friend bool operator<=(ScalarType lhs, const_reference rhs) noexcept(std::is_nothrow_constructible<detail::uncvref_t<decltype(rhs)>, ScalarType>::value)
    {
        return basic_json(lhs) <= rhs;
    }
@@ -5225,7 +5358,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    /// @sa https://json.nlohmann.me/api/basic_json/operator_gt/
    template<typename ScalarType, typename std::enable_if<
                 std::is_scalar<ScalarType>::value, int>::type = 0>
-    friend bool operator>(const_reference lhs, ScalarType rhs) noexcept(std::is_nothrow_constructible<basic_json, ScalarType>::value)
+    friend bool operator>(const_reference lhs, ScalarType rhs) noexcept(std::is_nothrow_constructible<detail::uncvref_t<decltype(lhs)>, ScalarType>::value)
    {
        return lhs > basic_json(rhs);
    }
@@ -5234,7 +5367,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    /// @sa https://json.nlohmann.me/api/basic_json/operator_gt/
    template<typename ScalarType, typename std::enable_if<
                 std::is_scalar<ScalarType>::value, int>::type = 0>
-    friend bool operator>(ScalarType lhs, const_reference rhs) noexcept(std::is_nothrow_constructible<basic_json, ScalarType>::value)
+    friend bool operator>(ScalarType lhs, const_reference rhs) noexcept(std::is_nothrow_constructible<detail::uncvref_t<decltype(rhs)>, ScalarType>::value)
    {
        return basic_json(lhs) > rhs;
    }
@@ -5254,7 +5387,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    /// @sa https://json.nlohmann.me/api/basic_json/operator_ge/
    template<typename ScalarType, typename std::enable_if<
                 std::is_scalar<ScalarType>::value, int>::type = 0>
-    friend bool operator>=(const_reference lhs, ScalarType rhs) noexcept(std::is_nothrow_constructible<basic_json, ScalarType>::value)
+    friend bool operator>=(const_reference lhs, ScalarType rhs) noexcept(std::is_nothrow_constructible<detail::uncvref_t<decltype(lhs)>, ScalarType>::value)
    {
        return lhs >= basic_json(rhs);
    }
@@ -5263,7 +5396,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    /// @sa https://json.nlohmann.me/api/basic_json/operator_ge/
    template<typename ScalarType, typename std::enable_if<
                 std::is_scalar<ScalarType>::value, int>::type = 0>
-    friend bool operator>=(ScalarType lhs, const_reference rhs) noexcept(std::is_nothrow_constructible<basic_json, ScalarType>::value)
+    friend bool operator>=(ScalarType lhs, const_reference rhs) noexcept(std::is_nothrow_constructible<detail::uncvref_t<decltype(rhs)>, ScalarType>::value)
    {
        return basic_json(lhs) >= rhs;
    }
@@ -5299,6 +5432,9 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
        return o;
    }

+#if !JSON_DELETE_DEPRECATED_FUNCTIONS
+    // the deleted version is a function template after the class, because
+    // GCC < 5 and Clang < 10 reject deleted friend functions in class templates
    /// @brief serialize to stream
    /// @sa https://json.nlohmann.me/api/operator_ltlt/
    /// @deprecated This function is deprecated since 3.0.0 and will be removed in
@@ -5310,6 +5446,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    {
        return o << j;
    }
+#endif
 #endif  // JSON_NO_IO
    /// @}

@@ -5361,12 +5498,16 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                            const bool allow_exceptions = true,
                            const bool ignore_comments = false,
                            const bool ignore_trailing_commas = false)
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+        = delete;
+#else
    {
        basic_json result;
        auto p = parser(i.get(), std::move(cb), allow_exceptions, ignore_comments, ignore_trailing_commas);
        p.parse(true, result);
        return result;
    }
+#endif

    /// @brief check if the input is valid JSON
    /// @sa https://json.nlohmann.me/api/basic_json/accept/
@@ -5396,9 +5537,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    static bool accept(detail::span_input_adapter&& i,
                       const bool ignore_comments = false,
                       const bool ignore_trailing_commas = false)
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+        = delete;
+#else
    {
        return parser(i.get(), nullptr, false, ignore_comments, ignore_trailing_commas, true).accept(true);
    }
+#endif

    /// @brief generate SAX events
    /// @sa https://json.nlohmann.me/api/basic_json/sax_parse/
@@ -5459,6 +5604,9 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                          const bool strict = true,
                          const bool ignore_comments = false,
                          const bool ignore_trailing_commas = false)
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+    = delete;
+#else
    {
        auto ia = i.get();
        return format == input_format_t::json
@@ -5467,10 +5615,14 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
               // NOLINTNEXTLINE(hicpp-move-const-arg,performance-move-const-arg)
               : detail::binary_reader<basic_json, decltype(ia), SAX>(std::move(ia), format).sax_parse(sax, strict);
    }
+#endif
 #if defined(__clang__)
 #pragma clang diagnostic pop
 #endif
 #ifndef JSON_NO_IO
+#if !JSON_DELETE_DEPRECATED_FUNCTIONS
+    // the deleted version is a function template after the class, because
+    // GCC < 5 and Clang < 10 reject deleted friend functions in class templates
    /// @brief deserialize from stream
    /// @sa https://json.nlohmann.me/api/operator_gtgt/
    /// @deprecated This stream operator is deprecated since 3.0.0 and will be removed in
@@ -5482,6 +5634,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    {
        return operator>>(i, j);
    }
+#endif

    /// @brief deserialize from stream
    /// @sa https://json.nlohmann.me/api/operator_gtgt/
@@ -5829,9 +5982,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                                const bool strict = true,
                                const bool allow_exceptions = true,
                                const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error)
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+    = delete;
+#else
    {
        return from_cbor(ptr, ptr + len, strict, allow_exceptions, tag_handler);
    }
+#endif

    JSON_HEDLEY_WARN_UNUSED_RESULT
    JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_cbor(ptr, ptr + len))
@@ -5839,9 +5996,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                                const bool strict = true,
                                const bool allow_exceptions = true,
                                const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error)
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+        = delete;
+#else
    {
        return from_binary_impl(i.get(), input_format_t::cbor, strict, allow_exceptions, error_handler_t::keep, tag_handler);
    }
+#endif

    /// @brief create a JSON value from an input in MessagePack format
    /// @sa https://json.nlohmann.me/api/basic_json/from_msgpack/
@@ -5874,18 +6035,26 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    static basic_json from_msgpack(const T* ptr, std::size_t len,
                                   const bool strict = true,
                                   const bool allow_exceptions = true)
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+    = delete;
+#else
    {
        return from_msgpack(ptr, ptr + len, strict, allow_exceptions);
    }
+#endif

    JSON_HEDLEY_WARN_UNUSED_RESULT
    JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_msgpack(ptr, ptr + len))
    static basic_json from_msgpack(detail::span_input_adapter&& i,
                                   const bool strict = true,
                                   const bool allow_exceptions = true)
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+        = delete;
+#else
    {
        return from_binary_impl(i.get(), input_format_t::msgpack, strict, allow_exceptions);
    }
+#endif

    /// @brief create a JSON value from an input in UBJSON format
    /// @sa https://json.nlohmann.me/api/basic_json/from_ubjson/
@@ -5918,18 +6087,26 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    static basic_json from_ubjson(const T* ptr, std::size_t len,
                                  const bool strict = true,
                                  const bool allow_exceptions = true)
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+    = delete;
+#else
    {
        return from_ubjson(ptr, ptr + len, strict, allow_exceptions);
    }
+#endif

    JSON_HEDLEY_WARN_UNUSED_RESULT
    JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_ubjson(ptr, ptr + len))
    static basic_json from_ubjson(detail::span_input_adapter&& i,
                                  const bool strict = true,
                                  const bool allow_exceptions = true)
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+        = delete;
+#else
    {
        return from_binary_impl(i.get(), input_format_t::ubjson, strict, allow_exceptions);
    }
+#endif

    /// @brief create a JSON value from an input in BJData format
    /// @sa https://json.nlohmann.me/api/basic_json/from_bjdata/
@@ -5956,6 +6133,20 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
        return from_binary_impl(detail::input_adapter(std::move(first), std::move(last)), input_format_t::bjdata, strict, allow_exceptions, error_handler);
    }

+    template<typename T>
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    JSON_HEDLEY_DEPRECATED_FOR(3.13.0, from_bjdata(ptr, ptr + len))
+    static basic_json from_bjdata(const T* ptr, std::size_t len,
+                                  const bool strict = true,
+                                  const bool allow_exceptions = true)
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+    = delete;
+#else
+    {
+        return from_bjdata(ptr, ptr + len, strict, allow_exceptions);
+    }
+#endif
+
    /// @brief create a JSON value from an input in BON8 format
    /// @sa https://json.nlohmann.me/api/basic_json/from_bon8/
    template<typename InputType>
@@ -5979,6 +6170,20 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
        return from_binary_impl(detail::input_adapter(std::move(first), std::move(last)), input_format_t::bon8, strict, allow_exceptions);
    }

+    template<typename T>
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    JSON_HEDLEY_DEPRECATED_FOR(3.13.0, from_bon8(ptr, ptr + len))
+    static basic_json from_bon8(const T* ptr, std::size_t len,
+                                const bool strict = true,
+                                const bool allow_exceptions = true)
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+    = delete;
+#else
+    {
+        return from_bon8(ptr, ptr + len, strict, allow_exceptions);
+    }
+#endif
+
    /// @brief create a JSON value from an input in BSON format
    /// @sa https://json.nlohmann.me/api/basic_json/from_bson/
    template<typename InputType>
@@ -6010,18 +6215,26 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    static basic_json from_bson(const T* ptr, std::size_t len,
                                const bool strict = true,
                                const bool allow_exceptions = true)
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+    = delete;
+#else
    {
        return from_bson(ptr, ptr + len, strict, allow_exceptions);
    }
+#endif

    JSON_HEDLEY_WARN_UNUSED_RESULT
    JSON_HEDLEY_DEPRECATED_FOR(3.8.0, from_bson(ptr, ptr + len))
    static basic_json from_bson(detail::span_input_adapter&& i,
                                const bool strict = true,
                                const bool allow_exceptions = true)
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+        = delete;
+#else
    {
        return from_binary_impl(i.get(), input_format_t::bson, strict, allow_exceptions);
    }
+#endif
    /// @}

    //////////////////////////
@@ -6041,9 +6254,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    template<typename BasicJsonType, detail::enable_if_t<detail::is_basic_json<BasicJsonType>::value, int> = 0>
    JSON_HEDLEY_DEPRECATED_FOR(3.11.0, basic_json::json_pointer or nlohmann::json_pointer<basic_json::string_t>) // NOLINT(readability/alt_tokens)
    reference operator[](const ::nlohmann::json_pointer<BasicJsonType>& ptr)
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+    = delete;
+#else
    {
        return ptr.get_unchecked(this);
    }
+#endif

    /// @brief access specified element via JSON Pointer
    /// @sa https://json.nlohmann.me/api/basic_json/operator%5B%5D/
@@ -6055,9 +6272,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    template<typename BasicJsonType, detail::enable_if_t<detail::is_basic_json<BasicJsonType>::value, int> = 0>
    JSON_HEDLEY_DEPRECATED_FOR(3.11.0, basic_json::json_pointer or nlohmann::json_pointer<basic_json::string_t>) // NOLINT(readability/alt_tokens)
    const_reference operator[](const ::nlohmann::json_pointer<BasicJsonType>& ptr) const
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+    = delete;
+#else
    {
        return ptr.get_unchecked(this);
    }
+#endif

    /// @brief access specified element via JSON Pointer
    /// @sa https://json.nlohmann.me/api/basic_json/at/
@@ -6069,9 +6290,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    template<typename BasicJsonType, detail::enable_if_t<detail::is_basic_json<BasicJsonType>::value, int> = 0>
    JSON_HEDLEY_DEPRECATED_FOR(3.11.0, basic_json::json_pointer or nlohmann::json_pointer<basic_json::string_t>) // NOLINT(readability/alt_tokens)
    reference at(const ::nlohmann::json_pointer<BasicJsonType>& ptr)
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+    = delete;
+#else
    {
        return ptr.get_checked(this);
    }
+#endif

    /// @brief access specified element via JSON Pointer
    /// @sa https://json.nlohmann.me/api/basic_json/at/
@@ -6083,9 +6308,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    template<typename BasicJsonType, detail::enable_if_t<detail::is_basic_json<BasicJsonType>::value, int> = 0>
    JSON_HEDLEY_DEPRECATED_FOR(3.11.0, basic_json::json_pointer or nlohmann::json_pointer<basic_json::string_t>) // NOLINT(readability/alt_tokens)
    const_reference at(const ::nlohmann::json_pointer<BasicJsonType>& ptr) const
+#if JSON_DELETE_DEPRECATED_FUNCTIONS
+    = delete;
+#else
    {
        return ptr.get_checked(this);
    }
+#endif

    /// @brief return flattened JSON value
    /// @sa https://json.nlohmann.me/api/basic_json/flatten/
@@ -7062,6 +7291,18 @@ std::string format_as(const NLOHMANN_BASIC_JSON_TPL& j)
    return j.dump();
 }

+#if JSON_DELETE_DEPRECATED_FUNCTIONS && !defined(JSON_NO_IO)
+    /// @brief serialize to stream (deleted; use operator<<(std::ostream&, const basic_json&))
+    /// @sa https://json.nlohmann.me/api/operator_ltlt/
+    NLOHMANN_BASIC_JSON_TPL_DECLARATION
+    std::ostream& operator>>(const NLOHMANN_BASIC_JSON_TPL& j, std::ostream& o) = delete;
+
+    /// @brief deserialize from stream (deleted; use operator>>(std::istream&, basic_json&))
+    /// @sa https://json.nlohmann.me/api/operator_gtgt/
+    NLOHMANN_BASIC_JSON_TPL_DECLARATION
+    std::istream& operator<<(NLOHMANN_BASIC_JSON_TPL& j, std::istream& i) = delete;
+#endif
+
 NLOHMANN_JSON_NAMESPACE_END

 ///////////////////////
@@ -67,6 +67,10 @@
    #define JSON_STRICT_BINARY_UTF8 0
 #endif

+#ifndef JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
+    #define JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS 0
+#endif
+
 #if JSON_DIAGNOSTICS
    #define NLOHMANN_JSON_ABI_TAG_DIAGNOSTICS _diag
 #else
@@ -109,14 +113,20 @@
    #define NLOHMANN_JSON_ABI_TAG_STRICT_BINARY_UTF8
 #endif

+#if JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
+    #define NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS _ekmo
+#else
+    #define NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS
+#endif
+
 #ifndef NLOHMANN_JSON_NAMESPACE_NO_VERSION
    #define NLOHMANN_JSON_NAMESPACE_NO_VERSION 0
 #endif

 // Construct the namespace ABI tags component
-#define NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g) json_abi ## a ## b ## c ## d ## e ## f ## g
-#define NLOHMANN_JSON_ABI_TAGS_CONCAT(a, b, c, d, e, f, g) \
-    NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g)
+#define NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g, h) json_abi ## a ## b ## c ## d ## e ## f ## g ## h
+#define NLOHMANN_JSON_ABI_TAGS_CONCAT(a, b, c, d, e, f, g, h) \
+    NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g, h)

 #define NLOHMANN_JSON_ABI_TAGS                                       \
    NLOHMANN_JSON_ABI_TAGS_CONCAT(                                   \
@@ -126,7 +136,8 @@
            NLOHMANN_JSON_ABI_TAG_BRACE_INIT_COPY_SEMANTICS,         \
            NLOHMANN_JSON_ABI_TAG_PRECISE_STREAM_POSITION,           \
            NLOHMANN_JSON_ABI_TAG_STRICT_NUL_HANDLING,               \
-            NLOHMANN_JSON_ABI_TAG_STRICT_BINARY_UTF8)
+            NLOHMANN_JSON_ABI_TAG_STRICT_BINARY_UTF8,                \
+            NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS)

 // Construct the namespace version component
 #define NLOHMANN_JSON_NAMESPACE_VERSION_CONCAT_EX(major, minor, patch) \
@@ -8,6 +8,7 @@ set(JSON_SIMDUTF_VERSION 9.1.0 CACHE STRING "The simdutf version used by JSON_Te

 set(JSON_32bitTest     AUTO CACHE STRING "Enable the 32bit unit test (ON/OFF/AUTO/ONLY).")
 set(JSON_TestStandards "" CACHE STRING "The list of standards to test explicitly.")
+set(JSON_TestShard     "" CACHE STRING "Build only a part of the unit tests, given as <index>/<count> (e.g. 0/2), to split them across CI jobs with a time limit.")

 # using an env var, since this will also affect targets executing cmake (such as "ci_test_compiler_default")
 if (NOT "" STREQUAL "$ENV{JSON_FORCED_GLOBAL_COMPILE_OPTIONS}")
@@ -288,6 +289,33 @@ elseif(NOT json_32bit_test)
    list(FILTER files EXCLUDE REGEX src/unit-32bit.cpp)
 endif()

+# with JSON_TestShard=<index>/<count>, keep every <count>-th unit test file,
+# starting at <index> (the glob is sorted, so the split is stable)
+set(test_shard_index 0)
+if(NOT "${JSON_TestShard}" STREQUAL "")
+    if(NOT JSON_TestShard MATCHES "^([0-9]+)/([1-9][0-9]*)$")
+        message(FATAL_ERROR "JSON_TestShard must be <index>/<count>, e.g. 0/2, not '${JSON_TestShard}'.")
+    endif()
+    set(test_shard_index ${CMAKE_MATCH_1})
+    set(test_shard_count ${CMAKE_MATCH_2})
+    if(NOT test_shard_index LESS test_shard_count)
+        message(FATAL_ERROR "JSON_TestShard: the index must be less than the count, not '${JSON_TestShard}'.")
+    endif()
+    list(LENGTH files test_file_count)
+    set(shard_files "")
+    set(file_position 0)
+    foreach(file ${files})
+        math(EXPR file_shard "${file_position} % ${test_shard_count}")
+        if(file_shard EQUAL test_shard_index)
+            list(APPEND shard_files ${file})
+        endif()
+        math(EXPR file_position "${file_position} + 1")
+    endforeach()
+    set(files ${shard_files})
+    list(LENGTH files shard_file_count)
+    message(STATUS "Test shard ${JSON_TestShard}: ${shard_file_count} of ${test_file_count} unit test files")
+endif()
+
 foreach(file ${files})
    json_test_add_test_for(${file} MAIN test_main CXX_STANDARDS ${test_cxx_standards} ${test_force})
 endforeach()
@@ -305,6 +333,9 @@ if(json_32bit_test_only)
    return()
 endif()

+# the following variants of single test files are only built in the first shard
+if(test_shard_index EQUAL 0)
+
 # test legacy comparison of discarded values
 json_test_set_test_options(test-comparison_legacy
    COMPILE_DEFINITIONS JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON=1
@@ -332,6 +363,8 @@ json_test_add_test_for(src/unit-diagnostic-positions.cpp
    MAIN test_main CXX_STANDARDS ${test_cxx_standards} ${test_force}
 )

+endif()
+
 # *DO NOT* use json_test_set_test_options() below this line

 #############################################################################
@@ -48,6 +48,10 @@ TEST_CASE("default namespace")
        expected += "_sbu8";
 #endif

+#if JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
+        expected += "_ekmo";
+#endif
+
        expected += "_v" STRINGIZE(NLOHMANN_JSON_VERSION_MAJOR);
        expected += "_" STRINGIZE(NLOHMANN_JSON_VERSION_MINOR);
        expected += "_" STRINGIZE(NLOHMANN_JSON_VERSION_PATCH) "::basic_json";
@@ -49,6 +49,10 @@ TEST_CASE("default namespace without version component")
        expected += "_sbu8";
 #endif

+#if JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
+        expected += "_ekmo";
+#endif
+
        expected += "::basic_json";

        // fallback for Clang
@@ -0,0 +1,599 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#pragma once
+
+#include <array> // array
+#include <cstdint> // uint32_t, uint64_t
+
+// Number tokens that are hard to round correctly, with the IEEE-754 binary64
+// and binary32 bits of their correctly rounded values (ties to even; infinity
+// for an overflow, a signed zero for an underflow).
+//
+// For doubles and floats around 0, the smallest normal number, 1, 2^24, 2^53,
+// 0.1, and the largest finite number, and for random ones, the exact midpoint
+// m to the next number gives: m, m with one unit more and less in the last
+// digit, m with "01" and "0...01" appended, m with trailing zeros, and m cut
+// after 17 to 30 digits (rounded down and up, so that the rounding is decided
+// after the 19th digit), in fixed and exponent notation, 30% of them negative.
+// Tokens longer than 80 characters are left out, except for four of 700 digits
+// and more. Zeros, underflow, overflow, huge exponents, and integers beyond 64
+// bits complete the set. Of the 508 tokens, 134 (as double) and 150 (as
+// float) need the exact comparison with the midpoint (detail::digit_comparison()).
+//
+// The expected bits were computed with exact rational arithmetic in Python
+// (fractions.Fraction) and cross-checked with Python's float(); strtod_l and
+// strtof_l of Apple's libc and of glibc agree. Generated by
+// compact_hard_cases.py 5 (with hard_cases.py), see the pull request that
+// added this file.
+
+namespace float_hard_cases
+{
+
+struct hard_case
+{
+    const char* token;
+    std::uint64_t bits64;
+    std::uint32_t bits32;
+};
+
+inline const std::array<hard_case, 508>& cases()
+{
+    static const std::array<hard_case, 508> table =
+    {
+        {
+            {"-2.4703282292062327e-324", 0x8000000000000000u, 0x80000000u},
+            {"24703282292062328e-340", 0x0000000000000001u, 0x00000000u},
+            {"247032822920623272e-341", 0x0000000000000000u, 0x00000000u},
+            {"-0.2470328229206232721e-323", 0x8000000000000001u, 0x80000000u},
+            {"-0.24703282292062327208e-323", 0x8000000000000000u, 0x80000000u},
+            {"-2.4703282292062327209e-324", 0x8000000000000001u, 0x80000000u},
+            {"2.47032822920623272088e-324", 0x0000000000000000u, 0x00000000u},
+            {"247032822920623272089e-344", 0x0000000000000001u, 0x00000000u},
+            {"-247032822920623272088284396434e-353", 0x8000000000000000u, 0x80000000u},
+            {"0.247032822920623272088284396435e-323", 0x0000000000000001u, 0x00000000u},
+            {"-74109846876186981e-340", 0x8000000000000001u, 0x80000000u},
+            {"0.74109846876186982e-323", 0x0000000000000002u, 0x00000000u},
+            {"-0.7410984687618698162e-323", 0x8000000000000001u, 0x80000000u},
+            {"-7.410984687618698163e-324", 0x8000000000000002u, 0x80000000u},
+            {"7.4109846876186981626e-324", 0x0000000000000001u, 0x00000000u},
+            {"-74109846876186981627e-343", 0x8000000000000002u, 0x80000000u},
+            {"-741098468761869816264e-344", 0x8000000000000001u, 0x80000000u},
+            {"0.741098468761869816265e-323", 0x0000000000000002u, 0x00000000u},
+            {"0.741098468761869816264853189302e-323", 0x0000000000000001u, 0x00000000u},
+            {"-7.41098468761869816264853189303e-324", 0x8000000000000002u, 0x80000000u},
+            {"0.22250738585072006e-307", 0x000FFFFFFFFFFFFEu, 0x00000000u},
+            {"2.2250738585072007e-308", 0x000FFFFFFFFFFFFFu, 0x00000000u},
+            {"2.225073858507200641e-308", 0x000FFFFFFFFFFFFEu, 0x00000000u},
+            {"-2225073858507200642e-326", 0x800FFFFFFFFFFFFFu, 0x80000000u},
+            {"22250738585072006419e-327", 0x000FFFFFFFFFFFFEu, 0x00000000u},
+            {"0.2225073858507200642e-307", 0x000FFFFFFFFFFFFFu, 0x00000000u},
+            {"0.222507385850720064199e-307", 0x000FFFFFFFFFFFFEu, 0x00000000u},
+            {"2.225073858507200642e-308", 0x000FFFFFFFFFFFFFu, 0x00000000u},
+            {"-2.22507385850720064199176395546e-308", 0x800FFFFFFFFFFFFEu, 0x80000000u},
+            {"222507385850720064199176395547e-337", 0x000FFFFFFFFFFFFFu, 0x00000000u},
+            {"-2.2250738585072011e-308", 0x800FFFFFFFFFFFFFu, 0x80000000u},
+            {"-22250738585072012e-324", 0x8010000000000000u, 0x80000000u},
+            {"-2225073858507201136e-326", 0x800FFFFFFFFFFFFFu, 0x80000000u},
+            {"0.2225073858507201137e-307", 0x0010000000000000u, 0x00000000u},
+            {"0.2225073858507201136e-307", 0x000FFFFFFFFFFFFFu, 0x00000000u},
+            {"-2.2250738585072011361e-308", 0x8010000000000000u, 0x80000000u},
+            {"2.22507385850720113605e-308", 0x000FFFFFFFFFFFFFu, 0x00000000u},
+            {"222507385850720113606e-328", 0x0010000000000000u, 0x00000000u},
+            {"22250738585072011360574097967e-336", 0x000FFFFFFFFFFFFFu, 0x00000000u},
+            {"0.222507385850720113605740979671e-307", 0x0010000000000000u, 0x00000000u},
+            {"22250738585072016e-324", 0x0010000000000000u, 0x00000000u},
+            {"0.22250738585072017e-307", 0x0010000000000001u, 0x00000000u},
+            {"0.222507385850720163e-307", 0x0010000000000000u, 0x00000000u},
+            {"2.225073858507201631e-308", 0x0010000000000001u, 0x00000000u},
+            {"-2.2250738585072016301e-308", 0x8010000000000000u, 0x80000000u},
+            {"22250738585072016302e-327", 0x0010000000000001u, 0x00000000u},
+            {"-222507385850720163012e-328", 0x8010000000000000u, 0x80000000u},
+            {"0.222507385850720163013e-307", 0x0010000000000001u, 0x00000000u},
+            {"0.222507385850720163012305563795e-307", 0x0010000000000000u, 0x00000000u},
+            {"-2.22507385850720163012305563796e-308", 0x8010000000000001u, 0x80000000u},
+            {"0.17976931348623156E+309", 0x7FEFFFFFFFFFFFFEu, 0x7F800000u},
+            {"1.7976931348623157e308", 0x7FEFFFFFFFFFFFFFu, 0x7F800000u},
+            {"1.797693134862315608e308", 0x7FEFFFFFFFFFFFFEu, 0x7F800000u},
+            {"-1797693134862315609e290", 0xFFEFFFFFFFFFFFFFu, 0xFF800000u},
+            {"-17976931348623156083e289", 0xFFEFFFFFFFFFFFFEu, 0xFF800000u},
+            {"-0.17976931348623156084E+309", 0xFFEFFFFFFFFFFFFFu, 0xFF800000u},
+            {"0.179769313486231560835E+309", 0x7FEFFFFFFFFFFFFEu, 0x7F800000u},
+            {"-1.79769313486231560836e308", 0xFFEFFFFFFFFFFFFFu, 0xFF800000u},
+            {"1.79769313486231560835325876058e308", 0x7FEFFFFFFFFFFFFEu, 0x7F800000u},
+            {"179769313486231560835325876059e279", 0x7FEFFFFFFFFFFFFFu, 0x7F800000u},
+            {"1.7976931348623158e308", 0x7FEFFFFFFFFFFFFFu, 0x7F800000u},
+            {"17976931348623159e292", 0x7FF0000000000000u, 0x7F800000u},
+            {"1797693134862315807e290", 0x7FEFFFFFFFFFFFFFu, 0x7F800000u},
+            {"0.1797693134862315808E+309", 0x7FF0000000000000u, 0x7F800000u},
+            {"0.17976931348623158079E+309", 0x7FEFFFFFFFFFFFFFu, 0x7F800000u},
+            {"-1.797693134862315808e308", 0xFFF0000000000000u, 0xFF800000u},
+            {"1.79769313486231580793e308", 0x7FEFFFFFFFFFFFFFu, 0x7F800000u},
+            {"179769313486231580794e288", 0x7FF0000000000000u, 0x7F800000u},
+            {"179769313486231580793728971405e279", 0x7FEFFFFFFFFFFFFFu, 0x7F800000u},
+            {"-0.179769313486231580793728971406E+309", 0xFFF0000000000000u, 0xFF800000u},
+            {"100000000000000011102230246251565404236316680908203125e-53", 0x3FF0000000000000u, 0x3F800000u},
+            {"-1.00000000000000011102230246251565404236316680908203126", 0xBFF0000000000001u, 0xBF800000u},
+            {"1.00000000000000011102230246251565404236316680908203124e0", 0x3FF0000000000000u, 0x3F800000u},
+            {"10000000000000001110223024625156540423631668090820312501e-55", 0x3FF0000000000001u, 0x3F800000u},
+            {"1.00000000000000011102230246251565404236316680908203125000000000000000000001", 0x3FF0000000000001u, 0x3F800000u},
+            {"10000000000000001e-16", 0x3FF0000000000000u, 0x3F800000u},
+            {"1.0000000000000002", 0x3FF0000000000001u, 0x3F800000u},
+            {"1.000000000000000111", 0x3FF0000000000000u, 0x3F800000u},
+            {"1.000000000000000112e0", 0x3FF0000000000001u, 0x3F800000u},
+            {"1.000000000000000111e0", 0x3FF0000000000000u, 0x3F800000u},
+            {"-10000000000000001111e-19", 0xBFF0000000000001u, 0xBF800000u},
+            {"-100000000000000011102e-20", 0xBFF0000000000000u, 0xBF800000u},
+            {"-1.00000000000000011103", 0xBFF0000000000001u, 0xBF800000u},
+            {"1.00000000000000011102230246251", 0x3FF0000000000000u, 0x3F800000u},
+            {"1.00000000000000011102230246252e0", 0x3FF0000000000001u, 0x3F800000u},
+            {"-0.999999999999999944488848768742172978818416595458984375", 0xBFF0000000000000u, 0xBF800000u},
+            {"-9.99999999999999944488848768742172978818416595458984376e-1", 0xBFF0000000000000u, 0xBF800000u},
+            {"999999999999999944488848768742172978818416595458984374e-54", 0x3FEFFFFFFFFFFFFFu, 0x3F800000u},
+            {"0.99999999999999994448884876874217297881841659545898437501", 0x3FF0000000000000u, 0x3F800000u},
+            {"9.99999999999999944488848768742172978818416595458984375000000000000000000001e-1", 0x3FF0000000000000u, 0x3F800000u},
+            {"-0.99999999999999994", 0xBFEFFFFFFFFFFFFFu, 0xBF800000u},
+            {"9.9999999999999995e-1", 0x3FF0000000000000u, 0x3F800000u},
+            {"9.999999999999999444e-1", 0x3FEFFFFFFFFFFFFFu, 0x3F800000u},
+            {"9999999999999999445e-19", 0x3FF0000000000000u, 0x3F800000u},
+            {"99999999999999994448e-20", 0x3FEFFFFFFFFFFFFFu, 0x3F800000u},
+            {"-0.99999999999999994449", 0xBFF0000000000000u, 0xBF800000u},
+            {"0.999999999999999944488", 0x3FEFFFFFFFFFFFFFu, 0x3F800000u},
+            {"-9.99999999999999944489e-1", 0xBFF0000000000000u, 0xBF800000u},
+            {"9.99999999999999944488848768742e-1", 0x3FEFFFFFFFFFFFFFu, 0x3F800000u},
+            {"999999999999999944488848768743e-30", 0x3FF0000000000000u, 0x3F800000u},
+            {"-9.007199254740993e15", 0xC340000000000000u, 0xDA000000u},
+            {"9007199254740994e0", 0x4340000000000001u, 0x5A000000u},
+            {"9007199254740992", 0x4340000000000000u, 0x5A000000u},
+            {"9.00719925474099301e15", 0x4340000000000001u, 0x5A000000u},
+            {"9007199254740993000000000000000000001e-21", 0x4340000000000001u, 0x5A000000u},
+            {"-9007199254740993.000000000000000000000000000000", 0xC340000000000000u, 0xDA000000u},
+            {"90071992547409915e-1", 0x4340000000000000u, 0x5A000000u},
+            {"-9007199254740991.6", 0xC340000000000000u, 0xDA000000u},
+            {"9.0071992547409914e15", 0x433FFFFFFFFFFFFFu, 0x5A000000u},
+            {"-9007199254740991501e-3", 0xC340000000000000u, 0xDA000000u},
+            {"9007199254740991.5000000000000000000001", 0x4340000000000000u, 0x5A000000u},
+            {"9.0071992547409915000000000000000000000000000000e15", 0x4340000000000000u, 0x5A000000u},
+            {"0.100000000000000012490009027033011079765856266021728515625", 0x3FB999999999999Au, 0x3DCCCCCDu},
+            {"1.00000000000000012490009027033011079765856266021728515626e-1", 0x3FB999999999999Bu, 0x3DCCCCCDu},
+            {"100000000000000012490009027033011079765856266021728515624e-57", 0x3FB999999999999Au, 0x3DCCCCCDu},
+            {"0.10000000000000001249000902703301107976585626602172851562501", 0x3FB999999999999Bu, 0x3DCCCCCDu},
+            {"0.10000000000000001", 0x3FB999999999999Au, 0x3DCCCCCDu},
+            {"1.0000000000000002e-1", 0x3FB999999999999Bu, 0x3DCCCCCDu},
+            {"-1.000000000000000124e-1", 0xBFB999999999999Au, 0xBDCCCCCDu},
+            {"1000000000000000125e-19", 0x3FB999999999999Bu, 0x3DCCCCCDu},
+            {"-10000000000000001249e-20", 0xBFB999999999999Au, 0xBDCCCCCDu},
+            {"0.1000000000000000125", 0x3FB999999999999Bu, 0x3DCCCCCDu},
+            {"0.10000000000000001249", 0x3FB999999999999Au, 0x3DCCCCCDu},
+            {"1.00000000000000012491e-1", 0x3FB999999999999Bu, 0x3DCCCCCDu},
+            {"1.00000000000000012490009027033e-1", 0x3FB999999999999Au, 0x3DCCCCCDu},
+            {"100000000000000012490009027034e-30", 0x3FB999999999999Bu, 0x3DCCCCCDu},
+            {"2.45134755833537796875e14", 0x42EBDE5C4164D83Au, 0x575EF2E2u},
+            {"-245134755833537796876e-6", 0xC2EBDE5C4164D83Au, 0xD75EF2E2u},
+            {"-245134755833537.796874", 0xC2EBDE5C4164D839u, 0xD75EF2E2u},
+            {"2.4513475583353779687501e14", 0x42EBDE5C4164D83Au, 0x575EF2E2u},
+            {"245134755833537796875000000000000000000001e-27", 0x42EBDE5C4164D83Au, 0x575EF2E2u},
+            {"245134755833537.796875000000000000000000000000000000", 0x42EBDE5C4164D83Au, 0x575EF2E2u},
+            {"2.4513475583353779e14", 0x42EBDE5C4164D839u, 0x575EF2E2u},
+            {"2451347558335378e-1", 0x42EBDE5C4164D83Au, 0x575EF2E2u},
+            {"2451347558335377968e-4", 0x42EBDE5C4164D839u, 0x575EF2E2u},
+            {"245134755833537.7969", 0x42EBDE5C4164D83Au, 0x575EF2E2u},
+            {"245134755833537.79687", 0x42EBDE5C4164D839u, 0x575EF2E2u},
+            {"2.4513475583353779688e14", 0x42EBDE5C4164D83Au, 0x575EF2E2u},
+            {"181510327827821147441864013671875e-23", 0x41DB0C11CB91CE38u, 0x4ED8608Eu},
+            {"-1815103278.27821147441864013671876", 0xC1DB0C11CB91CE38u, 0xCED8608Eu},
+            {"1.81510327827821147441864013671874e9", 0x41DB0C11CB91CE37u, 0x4ED8608Eu},
+            {"18151032782782114744186401367187501e-25", 0x41DB0C11CB91CE38u, 0x4ED8608Eu},
+            {"1815103278.27821147441864013671875000000000000000000001", 0x41DB0C11CB91CE38u, 0x4ED8608Eu},
+            {"-1.81510327827821147441864013671875000000000000000000000000000000e9", 0xC1DB0C11CB91CE38u, 0xCED8608Eu},
+            {"18151032782782114e-7", 0x41DB0C11CB91CE37u, 0x4ED8608Eu},
+            {"1815103278.2782115", 0x41DB0C11CB91CE38u, 0x4ED8608Eu},
+            {"1815103278.278211474", 0x41DB0C11CB91CE37u, 0x4ED8608Eu},
+            {"-1.815103278278211475e9", 0xC1DB0C11CB91CE38u, 0xCED8608Eu},
+            {"1.8151032782782114744e9", 0x41DB0C11CB91CE37u, 0x4ED8608Eu},
+            {"-18151032782782114745e-10", 0xC1DB0C11CB91CE38u, 0xCED8608Eu},
+            {"181510327827821147441e-11", 0x41DB0C11CB91CE37u, 0x4ED8608Eu},
+            {"1815103278.27821147442", 0x41DB0C11CB91CE38u, 0x4ED8608Eu},
+            {"1815103278.27821147441864013671", 0x41DB0C11CB91CE37u, 0x4ED8608Eu},
+            {"1.81510327827821147441864013672e9", 0x41DB0C11CB91CE38u, 0x4ED8608Eu},
+            {"3809325632181785344", 0x43CA6EB8BD69FE2Au, 0x5E5375C6u},
+            {"3.809325632181785345e18", 0x43CA6EB8BD69FE2Au, 0x5E5375C6u},
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+            {"5.03719055e8", 0x41BE06248F000000u, 0x4DF03124u},
+            {"50371905601e-2", 0x41BE062490028F5Cu, 0x4DF03125u},
+            {"503719056.000000000000000000001", 0x41BE062490000000u, 0x4DF03125u},
+            {"5.03719056000000000000000000000000000000e8", 0x41BE062490000000u, 0x4DF03124u},
+            {"-92331620", 0xC196037990000000u, 0xCCB01BCCu},
+            {"9.233163e7", 0x41960379B8000000u, 0x4CB01BCEu},
+            {"9233161e1", 0x4196037968000000u, 0x4CB01BCBu},
+            {"92331620.1", 0x4196037990666666u, 0x4CB01BCDu},
+            {"9.233162000000000000000000001e7", 0x4196037990000000u, 0x4CB01BCDu},
+            {"9233162000000000000000000000000000000e-29", 0x4196037990000000u, 0x4CB01BCCu},
+            {"3.002458625e6", 0x4146E82D50000000u, 0x4A37416Au},
+            {"3002458626e-3", 0x4146E82D5020C49Cu, 0x4A37416Bu},
+            {"3002458.624", 0x4146E82D4FDF3B64u, 0x4A37416Au},
+            {"-3.00245862501e6", 0xC146E82D500053E3u, 0xCA37416Bu},
+            {"3002458625000000000000000000001e-24", 0x4146E82D50000000u, 0x4A37416Bu},
+            {"3002458.625000000000000000000000000000000", 0x4146E82D50000000u, 0x4A37416Au},
+            {"-1095485584696182596504479582065262592e1", 0xC7A07BA830000000u, 0xFD03DD42u},
+            {"10954855846961825965044795820652625930", 0x47A07BA830000000u, 0x7D03DD42u},
+            {"1.095485584696182596504479582065262591e37", 0x47A07BA830000000u, 0x7D03DD41u},
+            {"109548558469618259650447958206526259201e-1", 0x47A07BA830000000u, 0x7D03DD42u},
+            {"-10954855846961825965044795820652625920.00000000000000000001", 0xC7A07BA830000000u, 0xFD03DD42u},
+            {"1.095485584696182596504479582065262592000000000000000000000000000000e37", 0x47A07BA830000000u, 0x7D03DD42u},
+            {"10954855846961825e21", 0x47A07BA830000000u, 0x7D03DD41u},
+            {"10954855846961826000000000000000000000", 0x47A07BA830000000u, 0x7D03DD42u},
+            {"10954855846961825960000000000000000000", 0x47A07BA830000000u, 0x7D03DD41u},
+            {"1.095485584696182597e37", 0x47A07BA830000000u, 0x7D03DD42u},
+            {"1.0954855846961825965e37", 0x47A07BA830000000u, 0x7D03DD41u},
+            {"-10954855846961825966e18", 0xC7A07BA830000000u, 0xFD03DD42u},
+            {"10954855846961825965e18", 0x47A07BA830000000u, 0x7D03DD41u},
+            {"10954855846961825965100000000000000000", 0x47A07BA830000000u, 0x7D03DD42u},
+            {"10954855846961825965044795820600000000", 0x47A07BA830000000u, 0x7D03DD41u},
+            {"-1.09548558469618259650447958207e37", 0xC7A07BA830000000u, 0xFD03DD42u},
+            {"1.6449216019182103706535606608388384863861375606575165875256061553955078126e-21", 0x3B9F125A50000000u, 0x1CF892D3u},
+            {"-16449216019182103706535606608388384863861375606575165875256061553955078124e-94", 0xBB9F125A50000000u, 0x9CF892D2u},
+            {"-0.0000000000000000000016449216019182103", 0xBB9F125A50000000u, 0x9CF892D2u},
+            {"-1.6449216019182104e-21", 0xBB9F125A50000000u, 0x9CF892D3u},
+            {"-1.64492160191821037e-21", 0xBB9F125A50000000u, 0x9CF892D2u},
+            {"-1644921601918210371e-39", 0xBB9F125A50000000u, 0x9CF892D3u},
+            {"-16449216019182103706e-40", 0xBB9F125A50000000u, 0x9CF892D2u},
+            {"0.0000000000000000000016449216019182103707", 0x3B9F125A50000000u, 0x1CF892D3u},
+            {"0.00000000000000000000164492160191821037065", 0x3B9F125A50000000u, 0x1CF892D2u},
+            {"1.64492160191821037066e-21", 0x3B9F125A50000000u, 0x1CF892D3u},
+            {"1.64492160191821037065356066083e-21", 0x3B9F125A50000000u, 0x1CF892D2u},
+            {"164492160191821037065356066084e-50", 0x3B9F125A50000000u, 0x1CF892D3u},
+            {"6.565061509609222412109375e-1", 0x3FE5021930000000u, 0x3F2810CAu},
+            {"6565061509609222412109376e-25", 0x3FE5021930000000u, 0x3F2810CAu},
+            {"0.6565061509609222412109374", 0x3FE5021930000000u, 0x3F2810C9u},
+            {"6.56506150960922241210937501e-1", 0x3FE5021930000000u, 0x3F2810CAu},
+            {"6565061509609222412109375000000000000000000001e-46", 0x3FE5021930000000u, 0x3F2810CAu},
+            {"-0.6565061509609222412109375000000000000000000000000000000", 0xBFE5021930000000u, 0xBF2810CAu},
+            {"6.5650615096092224e-1", 0x3FE5021930000000u, 0x3F2810C9u},
+            {"-65650615096092225e-17", 0xBFE5021930000000u, 0xBF2810CAu},
+            {"6565061509609222412e-19", 0x3FE5021930000000u, 0x3F2810C9u},
+            {"0.6565061509609222413", 0x3FE5021930000000u, 0x3F2810CAu},
+            {"0.65650615096092224121", 0x3FE5021930000000u, 0x3F2810C9u},
+            {"6.5650615096092224122e-1", 0x3FE5021930000000u, 0x3F2810CAu},
+            {"-6.5650615096092224121e-1", 0xBFE5021930000000u, 0xBF2810C9u},
+            {"656506150960922241211e-21", 0x3FE5021930000000u, 0x3F2810CAu},
+            {"18014627239033005156980393746124491372029297053813934326171875e-77", 0x3CA9F63970000000u, 0x254FB1CCu},
+            {"0.00000000000000018014627239033005156980393746124491372029297053813934326171876", 0x3CA9F63970000000u, 0x254FB1CCu},
+            {"-1.8014627239033005156980393746124491372029297053813934326171874e-16", 0xBCA9F63970000000u, 0xA54FB1CBu},
+            {"1801462723903300515698039374612449137202929705381393432617187501e-79", 0x3CA9F63970000000u, 0x254FB1CCu},
+            {"18014627239033005e-32", 0x3CA9F63970000000u, 0x254FB1CBu},
+            {"0.00000000000000018014627239033006", 0x3CA9F63970000000u, 0x254FB1CCu},
+            {"0.0000000000000001801462723903300515", 0x3CA9F63970000000u, 0x254FB1CBu},
+            {"-1.801462723903300516e-16", 0xBCA9F63970000000u, 0xA54FB1CCu},
+            {"-1.8014627239033005156e-16", 0xBCA9F63970000000u, 0xA54FB1CBu},
+            {"18014627239033005157e-35", 0x3CA9F63970000000u, 0x254FB1CCu},
+            {"180146272390330051569e-36", 0x3CA9F63970000000u, 0x254FB1CBu},
+            {"-0.00000000000000018014627239033005157", 0xBCA9F63970000000u, 0xA54FB1CCu},
+            {"0.000000000000000180146272390330051569803937461", 0x3CA9F63970000000u, 0x254FB1CBu},
+            {"1.80146272390330051569803937462e-16", 0x3CA9F63970000000u, 0x254FB1CCu},
+            {"0.05534819327294826507568359375", 0x3FAC569930000000u, 0x3D62B4CAu},
+            {"-5.534819327294826507568359376e-2", 0xBFAC569930000000u, 0xBD62B4CAu},
+            {"5534819327294826507568359374e-29", 0x3FAC569930000000u, 0x3D62B4C9u},
+            {"-0.0553481932729482650756835937501", 0xBFAC569930000000u, 0xBD62B4CAu},
+            {"5.534819327294826507568359375000000000000000000001e-2", 0x3FAC569930000000u, 0x3D62B4CAu},
+            {"5534819327294826507568359375000000000000000000000000000000e-59", 0x3FAC569930000000u, 0x3D62B4CAu},
+            {"0.055348193272948265", 0x3FAC569930000000u, 0x3D62B4C9u},
+            {"5.5348193272948266e-2", 0x3FAC569930000000u, 0x3D62B4CAu},
+            {"5.534819327294826507e-2", 0x3FAC569930000000u, 0x3D62B4C9u},
+            {"5534819327294826508e-20", 0x3FAC569930000000u, 0x3D62B4CAu},
+            {"55348193272948265075e-21", 0x3FAC569930000000u, 0x3D62B4C9u},
+            {"-0.055348193272948265076", 0xBFAC569930000000u, 0xBD62B4CAu},
+            {"0.0553481932729482650756", 0x3FAC569930000000u, 0x3D62B4C9u},
+            {"-5.53481932729482650757e-2", 0xBFAC569930000000u, 0xBD62B4CAu},
+            {"5.179692133247783258005389047985340416e36", 0x478F2C9450000000u, 0x7C7964A2u},
+            {"5179692133247783258005389047985340417e0", 0x478F2C9450000000u, 0x7C7964A3u},
+            {"5179692133247783258005389047985340415", 0x478F2C9450000000u, 0x7C7964A2u},
+            {"-5.17969213324778325800538904798534041601e36", 0xC78F2C9450000000u, 0xFC7964A3u},
+            {"-5179692133247783258005389047985340416000000000000000000001e-21", 0xC78F2C9450000000u, 0xFC7964A3u},
+            {"-5179692133247783258005389047985340416.000000000000000000000000000000", 0xC78F2C9450000000u, 0xFC7964A2u},
+            {"5.1796921332477832e36", 0x478F2C9450000000u, 0x7C7964A2u},
+            {"51796921332477833e20", 0x478F2C9450000000u, 0x7C7964A3u},
+            {"-5179692133247783258e18", 0xC78F2C9450000000u, 0xFC7964A2u},
+            {"5179692133247783259000000000000000000", 0x478F2C9450000000u, 0x7C7964A3u},
+            {"5179692133247783258000000000000000000", 0x478F2C9450000000u, 0x7C7964A2u},
+            {"5.1796921332477832581e36", 0x478F2C9450000000u, 0x7C7964A3u},
+            {"-5.179692133247783258e36", 0xC78F2C9450000000u, 0xFC7964A2u},
+            {"-517969213324778325801e16", 0xC78F2C9450000000u, 0xFC7964A3u},
+            {"517969213324778325800538904798e7", 0x478F2C9450000000u, 0x7C7964A2u},
+            {"5179692133247783258005389047990000000", 0x478F2C9450000000u, 0x7C7964A3u},
+            {
+                "0.22250738585072011360574097967091319759348195463516456480234261097248222220210769455165295239081350"
+                "8791414915891303962110687008643869459464552765720740782062174337998814106326732925355228688137214901"
+                "2981122451451889849057222307285255133155755015914397476397983411801999323962548289017107081850690630"
+                "6666559949382757725720157630626906633326475653000092458883164330377797918696120494973903778297049050"
+                "5108060994073026293712895895000358379996720725430436028407889577179615094551674824347103070260914462"
+                "1572289880258182545180325707018860872113128079512233426288368622321503775666622503982534335974568884"
+                "4239002654981983854879482922068947216898310996983658468140228542433306603398508864458040010349339704"
+                "2756718644338377048603786162277173854562306587467901408672332763671875e-307", 0x0010000000000000u, 0x00000000u
+            },
+            {
+                "2.22507385850720113605740979670913197593481954635164564802342610972482222202107694551652952390813508"
+                "7914149158913039621106870086438694594645527657207407820621743379988141063267329253552286881372149012"
+                "9811224514518898490572223072852551331557550159143974763979834118019993239625482890171070818506906306"
+                "6665599493827577257201576306269066333264756530000924588831643303777979186961204949739037782970490505"
+                "1080609940730262937128958950003583799967207254304360284078895771796150945516748243471030702609144621"
+                "5722898802581825451803257070188608721131280795122334262883686223215037756666225039825343359745688844"
+                "2390026549819838548794829220689472168983109969836584681402285424333066033985088644580400103493397042"
+                "756718644338377048603786162277173854562306587467901408672332763671875000000000000000000001e-308", 0x0010000000000000u, 0x00000000u
+            },
+            {
+                "0.11754942807573642917278829910357665133228589927589904276829631184250030649651730385585324256680905"
+                "8189392089843750000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+                "00000000000000000000000000000000000000000000000000000000000000000e-37", 0x380FFFFFE0000000u, 0x00800000u
+            },
+            {
+                "1175494280757364291727882991035766513322858992758990427682963118425003064965173038558532425668090581"
+                "8939208984375000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+                "00000000000001e-751", 0x380FFFFFE0000000u, 0x00800000u
+            },
+            {"0", 0x0000000000000000u, 0x00000000u},
+            {"-0", 0x8000000000000000u, 0x80000000u},
+            {"0.0", 0x0000000000000000u, 0x00000000u},
+            {"-0.0", 0x8000000000000000u, 0x80000000u},
+            {"0e999999999999999999999", 0x0000000000000000u, 0x00000000u},
+            {"-0.000e-99999", 0x8000000000000000u, 0x80000000u},
+            {"1e-400", 0x0000000000000000u, 0x00000000u},
+            {"-1e-400", 0x8000000000000000u, 0x80000000u},
+            {"1e400", 0x7FF0000000000000u, 0x7F800000u},
+            {"-1e400", 0xFFF0000000000000u, 0xFF800000u},
+            {"1e-50", 0x358DEE7A4AD4B81Fu, 0x00000000u},
+            {"-1e-50", 0xB58DEE7A4AD4B81Fu, 0x80000000u},
+            {"1e39", 0x48078287F49C4A1Du, 0x7F800000u},
+            {"-1e39", 0xC8078287F49C4A1Du, 0xFF800000u},
+            {"1e99999999999999999999999999", 0x7FF0000000000000u, 0x7F800000u},
+            {"1e-99999999999999999999999999", 0x0000000000000000u, 0x00000000u},
+            {"1e0000000000000000000000000000000000000000308", 0x7FE1CCF385EBC8A0u, 0x7F800000u},
+            {"123456789012345678901234567890e-30", 0x3FBF9ADD3746F65Fu, 0x3DFCD6EAu},
+            {"18446744073709551615", 0x43F0000000000000u, 0x5F800000u},
+            {"18446744073709551616", 0x43F0000000000000u, 0x5F800000u},
+            {"-9223372036854775808", 0xC3E0000000000000u, 0xDF000000u},
+            {"-9223372036854775809", 0xC3E0000000000000u, 0xDF000000u},
+        }
+    };
+    return table;
+}
+
+} // namespace float_hard_cases
@@ -521,6 +521,10 @@ struct countdown_allocator : std::allocator<T>

 TEST_CASE("converting a deeply nested value from another specialization fails cleanly (#5650)")
 {
+    // MSVC 2015's debug STL constructs the containers' debug proxies through
+    // the allocator in noexcept constructors, so a failing construction crashes
+    // the program there instead of throwing std::bad_alloc. Nothing to check.
+#if !(defined(_MSC_VER) && _MSC_VER < 1910 && defined(_ITERATOR_DEBUG_LEVEL) && _ITERATOR_DEBUG_LEVEL > 0)
    using countdown_json = nlohmann::basic_json<std::map,
          std::vector,
          std::string,
@@ -558,6 +562,7 @@ TEST_CASE("converting a deeply nested value from another specialization fails cl
        }
    }
    CHECK(failures > 0);
+#endif
 }

 namespace
@@ -602,3 +607,88 @@ TEST_CASE("bad my_allocator::construct")
        j["test"].push_back("should not leak");
    }
 }
+
+namespace
+{
+std::size_t counting_allocator_allocations = 0;
+std::size_t counting_allocator_deallocations = 0;
+
+template<class T>
+struct counting_allocator : std::allocator<T>
+{
+    using std::allocator<T>::allocator;
+
+    T* allocate(std::size_t n)
+    {
+        ++counting_allocator_allocations;
+        return std::allocator<T>::allocate(n);
+    }
+
+    void deallocate(T* p, std::size_t n)
+    {
+        ++counting_allocator_deallocations;
+        std::allocator<T>::deallocate(p, n);
+    }
+
+    template <class U>
+    struct rebind
+    {
+        using other = counting_allocator<U>;
+    };
+};
+} // namespace
+
+TEST_CASE("destructor performs no allocation, only deallocation")
+{
+    // see https://github.com/nlohmann/json/issues/4842 and
+    // https://github.com/nlohmann/json/issues/5135: destroying nested
+    // arrays/objects used to allocate a temporary stack (first with
+    // std::allocator, later - after #4842 - with the provided allocator).
+    // Since that stack could itself throw bad_alloc from inside the
+    // noexcept destructor (#5135), destroy() no longer allocates anything:
+    // it only ever frees what is already there.
+    using counting_json = nlohmann::basic_json<std::map,
+          std::vector,
+          std::string,
+          bool,
+          std::int64_t,
+          std::uint64_t,
+          double,
+          counting_allocator>;
+
+    SECTION("array")
+    {
+        auto* j = new counting_json({1, {2, {3, 4}}, 5}); // NOLINT(cppcoreguidelines-owning-memory)
+        const auto allocations_before = counting_allocator_allocations;
+        const auto deallocations_before = counting_allocator_deallocations;
+        delete j; // NOLINT(cppcoreguidelines-owning-memory)
+        CHECK(counting_allocator_allocations == allocations_before);
+        CHECK(counting_allocator_deallocations > deallocations_before);
+    }
+
+    SECTION("object")
+    {
+        auto* j = new counting_json({{"a", {{"b", {1, 2}}}}, {"c", 3}}); // NOLINT(cppcoreguidelines-owning-memory)
+        const auto allocations_before = counting_allocator_allocations;
+        const auto deallocations_before = counting_allocator_deallocations;
+        delete j; // NOLINT(cppcoreguidelines-owning-memory)
+        CHECK(counting_allocator_allocations == allocations_before);
+        CHECK(counting_allocator_deallocations > deallocations_before);
+    }
+
+    SECTION("mixed tree of empty/non-empty arrays and objects")
+    {
+        auto* j = new counting_json( // NOLINT(cppcoreguidelines-owning-memory)
+        {
+            {"empty_obj", counting_json::object()},
+            {"empty_arr", counting_json::array()},
+            {"nested", {{"a", counting_json::array({1, 2, counting_json::object()})}, {"b", 3}}},
+            {"tail", counting_json::array({counting_json::array({1}), 2, counting_json::array({3})})}
+        });
+        const auto allocations_before = counting_allocator_allocations;
+        const auto deallocations_before = counting_allocator_deallocations;
+        delete j; // NOLINT(cppcoreguidelines-owning-memory)
+        CHECK(counting_allocator_allocations == allocations_before);
+        CHECK(counting_allocator_deallocations > deallocations_before);
+    }
+}
@@ -11,7 +11,12 @@
 #include <nlohmann/json.hpp>
 using nlohmann::json;

+#include <cmath>
 #include <fstream>
+#include <limits>
+#include <map>
+#include <string>
+#include <vector>
 #include "make_test_data_available.hpp"

 TEST_CASE("Binary Formats" * doctest::skip())
@@ -33,7 +38,7 @@ TEST_CASE("Binary Formats" * doctest::skip())
        const auto ubjson_2_size = json::to_ubjson(j, true).size();
        const auto ubjson_3_size = json::to_ubjson(j, true, true).size();

-        CHECK(json_size == 2090303);
+        CHECK(json_size == 2090234);
        CHECK(bjdata_1_size == 1112030);
        CHECK(bjdata_2_size == 1224148);
        CHECK(bjdata_3_size == 1224148);
@@ -46,16 +51,16 @@ TEST_CASE("Binary Formats" * doctest::skip())
        CHECK(ubjson_3_size == 1169069);

        CHECK((100.0 * double(json_size) / double(json_size)) == Approx(100.0));
-        CHECK((100.0 * double(bjdata_1_size) / double(json_size)) == Approx(53.199));
-        CHECK((100.0 * double(bjdata_2_size) / double(json_size)) == Approx(58.563));
-        CHECK((100.0 * double(bjdata_3_size) / double(json_size)) == Approx(58.563));
-        CHECK((100.0 * double(bon8_size) / double(json_size)) == Approx(50.509));
-        CHECK((100.0 * double(bson_size) / double(json_size)) == Approx(85.849));
-        CHECK((100.0 * double(cbor_size) / double(json_size)) == Approx(50.497));
-        CHECK((100.0 * double(msgpack_size) / double(json_size)) == Approx(50.526));
-        CHECK((100.0 * double(ubjson_1_size) / double(json_size)) == Approx(53.199));
-        CHECK((100.0 * double(ubjson_2_size) / double(json_size)) == Approx(58.563));
-        CHECK((100.0 * double(ubjson_3_size) / double(json_size)) == Approx(55.928));
+        CHECK((100.0 * double(bjdata_1_size) / double(json_size)) == Approx(53.201));
+        CHECK((100.0 * double(bjdata_2_size) / double(json_size)) == Approx(58.565));
+        CHECK((100.0 * double(bjdata_3_size) / double(json_size)) == Approx(58.565));
+        CHECK((100.0 * double(bon8_size) / double(json_size)) == Approx(50.511));
+        CHECK((100.0 * double(bson_size) / double(json_size)) == Approx(85.853));
+        CHECK((100.0 * double(cbor_size) / double(json_size)) == Approx(50.499));
+        CHECK((100.0 * double(msgpack_size) / double(json_size)) == Approx(50.528));
+        CHECK((100.0 * double(ubjson_1_size) / double(json_size)) == Approx(53.201));
+        CHECK((100.0 * double(ubjson_2_size) / double(json_size)) == Approx(58.565));
+        CHECK((100.0 * double(ubjson_3_size) / double(json_size)) == Approx(55.930));
    }

    SECTION("twitter.json")
@@ -224,3 +229,139 @@ TEST_CASE("Binary Formats" * doctest::skip())
        CHECK((100.0 * double(ubjson_3_size) / double(json_size)) == Approx(89.450));
    }
 }
+
+namespace
+{
+// the binary formats as function pointers for "Binary formats with narrow number types";
+// named functions rather than lambdas, because clang 3.5 cannot convert a lambda
+// to a function pointer in the braced initializer of the format table
+using narrow_json = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int32_t, std::uint32_t, float>;
+using bytes = std::vector<std::uint8_t>;
+
+bytes encode_cbor(const json& j)
+{
+    return json::to_cbor(j);
+}
+narrow_json decode_cbor(const bytes& v, bool allow_exceptions)
+{
+    return narrow_json::from_cbor(v, true, allow_exceptions);
+}
+
+bytes encode_msgpack(const json& j)
+{
+    return json::to_msgpack(j);
+}
+narrow_json decode_msgpack(const bytes& v, bool allow_exceptions)
+{
+    return narrow_json::from_msgpack(v, true, allow_exceptions);
+}
+
+bytes encode_ubjson(const json& j)
+{
+    return json::to_ubjson(j);
+}
+narrow_json decode_ubjson(const bytes& v, bool allow_exceptions)
+{
+    return narrow_json::from_ubjson(v, true, allow_exceptions);
+}
+
+bytes encode_bjdata(const json& j)
+{
+    return json::to_bjdata(j);
+}
+narrow_json decode_bjdata(const bytes& v, bool allow_exceptions)
+{
+    return narrow_json::from_bjdata(v, true, allow_exceptions);
+}
+
+// BSON can only store numbers as object members
+bytes encode_bson(const json& j)
+{
+    return json::to_bson(json{{"a", j}});
+}
+narrow_json decode_bson(const bytes& v, bool allow_exceptions)
+{
+    const auto result = narrow_json::from_bson(v, true, allow_exceptions);
+    return result.is_discarded() ? result : result.at("a");
+}
+
+bytes encode_bon8(const json& j)
+{
+    return json::to_bon8(j);
+}
+narrow_json decode_bon8(const bytes& v, bool allow_exceptions)
+{
+    return narrow_json::from_bon8(v, true, allow_exceptions);
+}
+
+} // namespace
+
+TEST_CASE("Binary formats with narrow number types")
+{
+    // Numbers that do not fit the number types are handled like the lexer
+    // handles them in JSON text: an integer that fits neither integer type is
+    // stored as a floating-point number, and a finite floating-point number
+    // that overflows number_float_t is rejected with out_of_range.406.
+    struct binary_format
+    {
+        const char* name;
+        bytes (*encode)(const json&);
+        narrow_json (*decode)(const bytes&, bool);
+    };
+
+    const std::vector<binary_format> formats =
+    {
+        {"CBOR", encode_cbor, decode_cbor},
+        {"MessagePack", encode_msgpack, decode_msgpack},
+        {"UBJSON", encode_ubjson, decode_ubjson},
+        {"BJData", encode_bjdata, decode_bjdata},
+        {"BSON", encode_bson, decode_bson},
+        {"BON8", encode_bon8, decode_bon8},
+    };
+
+    for (const auto& format : formats)
+    {
+        const std::string name = format.name;
+        INFO("format := ", name);
+        const auto roundtrip = [&format](const json & j)
+        {
+            return format.decode(format.encode(j), true);
+        };
+
+        // integers that fit keep their type
+        CHECK(roundtrip(json(-5)).is_number_integer());
+        CHECK(roundtrip(json(-5)).get<std::int32_t>() == -5);
+        CHECK(roundtrip(json(3000000000u)).is_number_unsigned());
+        CHECK(roundtrip(json(3000000000u)).get<std::uint32_t>() == 3000000000u);
+
+        // integers that fit neither integer type are stored as float
+        CHECK(roundtrip(json(5000000000u)).is_number_float());
+        CHECK(roundtrip(json(5000000000u)).get<float>() == 5000000000.0f);
+        if (name != "BON8") // BON8 cannot encode integers above INT64_MAX
+        {
+            CHECK(roundtrip(json(10000000000000000000u)).is_number_float());
+            CHECK(roundtrip(json(10000000000000000000u)).get<float>() == 10000000000000000000.0f);
+        }
+        CHECK(roundtrip(json(-3000000000LL)).is_number_float());
+        CHECK(roundtrip(json(-3000000000LL)).get<float>() == -3000000000.0f);
+        CHECK(roundtrip(json(-5000000000LL)).is_number_float());
+        CHECK(roundtrip(json(-5000000000LL)).get<float>() == -5000000000.0f);
+
+        // floating-point numbers that fit
+        CHECK(roundtrip(json(1.5)).get<float>() == 1.5f);
+        const auto just_above_max = std::nextafter(static_cast<double>((std::numeric_limits<float>::max)()),
+                                    std::numeric_limits<double>::infinity());
+        CHECK(roundtrip(json(just_above_max)).get<float>() == (std::numeric_limits<float>::max)());
+
+        // infinity and NaN are passed on
+        CHECK(std::isinf(roundtrip(json(std::numeric_limits<double>::infinity())).get<float>()));
+        CHECK(std::isnan(roundtrip(json(std::numeric_limits<double>::quiet_NaN())).get<float>()));
+
+        // finite floating-point numbers that overflow number_float_t are rejected
+        const std::string message = "[json.exception.out_of_range.406] syntax error while parsing " + name
+                                    + " value: number overflow";
+        CHECK_THROWS_WITH_AS(roundtrip(json(1e300)), message.c_str(), narrow_json::out_of_range&);
+        CHECK_THROWS_WITH_AS(roundtrip(json(-1e300)), message.c_str(), narrow_json::out_of_range&);
+        CHECK(format.decode(format.encode(json(1e300)), false).is_discarded());
+    }
+}
@@ -9,6 +9,14 @@
 #include "doctest_compatibility.h"

 #define JSON_TESTS_PRIVATE
+// capture whether JSON_DELETE_DEPRECATED_FUNCTIONS was enabled on the command
+// line *before* including json.hpp, since the library #undefs it once the header
+// has been fully processed (see include/nlohmann/detail/macro_unscope.hpp); the
+// tests of deprecated functions are skipped if these functions are deleted
+#if defined(JSON_DELETE_DEPRECATED_FUNCTIONS) && (JSON_DELETE_DEPRECATED_FUNCTIONS == 1)
+    #define JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
+#endif
+
 #include <nlohmann/json.hpp>
 using nlohmann::json;

@@ -106,10 +114,59 @@ TEST_CASE("BJData")
    {
        SECTION("discarded")
        {
-            // discarded values are not serialized
+            // a discarded value cannot be serialized to BJData
            json const j = json::value_t::discarded;
-            const auto result = json::to_bjdata(j);
-            CHECK(result.empty());
+            CHECK_THROWS_WITH_AS(json::to_bjdata(j), "[json.exception.type_error.321] cannot serialize discarded value to BJData", json::type_error&);
+        }
+
+        SECTION("discarded values nested in a container")
+        {
+            json const discarded = json::value_t::discarded;
+
+            SECTION("in an array")
+            {
+                json const j = {1, discarded, 2};
+#if JSON_DIAGNOSTICS
+                CHECK_THROWS_WITH_AS(json::to_bjdata(j), "[json.exception.type_error.321] (/1) cannot serialize discarded value to BJData", json::type_error&);
+#else
+                CHECK_THROWS_WITH_AS(json::to_bjdata(j), "[json.exception.type_error.321] cannot serialize discarded value to BJData", json::type_error&);
+#endif
+            }
+
+            SECTION("as an object value")
+            {
+                json j;
+                j["a"] = 1;
+                j["b"] = discarded;
+#if JSON_DIAGNOSTICS
+                CHECK_THROWS_WITH_AS(json::to_bjdata(j), "[json.exception.type_error.321] (/b) cannot serialize discarded value to BJData", json::type_error&);
+#else
+                CHECK_THROWS_WITH_AS(json::to_bjdata(j), "[json.exception.type_error.321] cannot serialize discarded value to BJData", json::type_error&);
+#endif
+            }
+
+            SECTION("nested deeper (array in object in array)")
+            {
+                json inner_array = {1, discarded};
+                json middle_object;
+                middle_object["x"] = inner_array;
+                json const j = {middle_object};
+#if JSON_DIAGNOSTICS
+                CHECK_THROWS_WITH_AS(json::to_bjdata(j), "[json.exception.type_error.321] (/0/x/1) cannot serialize discarded value to BJData", json::type_error&);
+#else
+                CHECK_THROWS_WITH_AS(json::to_bjdata(j), "[json.exception.type_error.321] cannot serialize discarded value to BJData", json::type_error&);
+#endif
+            }
+
+            SECTION("optimized array of all-discarded elements")
+            {
+                json const j = {discarded, discarded};
+#if JSON_DIAGNOSTICS
+                CHECK_THROWS_WITH_AS(json::to_bjdata(j, true, true), "[json.exception.type_error.321] (/0) cannot serialize discarded value to BJData", json::type_error&);
+#else
+                CHECK_THROWS_WITH_AS(json::to_bjdata(j, true, true), "[json.exception.type_error.321] cannot serialize discarded value to BJData", json::type_error&);
+#endif
+            }
        }

        SECTION("null")
@@ -4490,3 +4547,33 @@ TEST_CASE("BJData roundtrips" * doctest::skip())
        }
    }
 }
+
+TEST_CASE("issue #5648 - from_bjdata(ptr, len) must read len bytes, not treat ptr as a C string")
+{
+    // to_bjdata() encodes the integer 0 as the two bytes 'i' 0x00 (a BJData
+    // type marker followed by the value byte 0x00), so the packed data
+    // below contains a 0x00 byte before its end.
+    const json j = {{"a", 0}};
+    const std::vector<std::uint8_t> packed = json::to_bjdata(j);
+    bool contains_nul = false;
+    for (const auto byte : packed)
+    {
+        contains_nul |= (byte == 0x00);
+    }
+    REQUIRE(contains_nul);
+
+#ifndef JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
+    // before the fix, from_bjdata had no (ptr, len) overload, so this call
+    // bound to from_bjdata(InputType&&, bool strict) instead: ptr was read
+    // as a NUL-terminated C string (stopping at the embedded 0x00 byte), and
+    // len was silently converted to the strict flag. The deprecated
+    // overload added for this issue forwards to from_bjdata(ptr, ptr + len,
+    // ...) instead, like from_ubjson's deprecated (ptr, len) overload does.
+    json result;
+    CHECK_NOTHROW(result = json::from_bjdata(packed.data(), packed.size()));
+    CHECK(result == j);
+
+    // len must not collapse into the strict flag either
+    CHECK(json::from_bjdata(packed.data(), packed.size(), false) == j);
+#endif
+}
@@ -8,6 +8,14 @@

 #include "doctest_compatibility.h"

+// capture whether JSON_DELETE_DEPRECATED_FUNCTIONS was enabled on the command
+// line *before* including json.hpp, since the library #undefs it once the header
+// has been fully processed (see include/nlohmann/detail/macro_unscope.hpp); the
+// tests of deprecated functions are skipped if these functions are deleted
+#if defined(JSON_DELETE_DEPRECATED_FUNCTIONS) && (JSON_DELETE_DEPRECATED_FUNCTIONS == 1)
+    #define JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
+#endif
+
 #include <nlohmann/json.hpp>
 using nlohmann::json;
 #ifdef JSON_TEST_NO_GLOBAL_UDLS
@@ -1014,6 +1022,36 @@ TEST_CASE("BON8 roundtrips" * doctest::skip())
    }
 }

+TEST_CASE("issue #5648 - from_bon8(ptr, len) must read len bytes, not treat ptr as a C string")
+{
+    // to_bon8() encodes the integer 40 as the two bytes 0xC2 0x00 (a BON8
+    // lead byte followed by a continuation byte of 0x00), so the packed data
+    // below contains a 0x00 byte before its end.
+    const json j = {{"a", 40}, {"b", "x"}};
+    const std::vector<std::uint8_t> packed = json::to_bon8(j);
+    bool contains_nul = false;
+    for (const auto byte : packed)
+    {
+        contains_nul |= (byte == 0x00);
+    }
+    REQUIRE(contains_nul);
+
+#ifndef JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
+    // before the fix, from_bon8 had no (ptr, len) overload, so this call
+    // bound to from_bon8(InputType&&, bool strict) instead: ptr was read as
+    // a NUL-terminated C string (stopping at the embedded 0x00 byte), and
+    // len was silently converted to the strict flag. The deprecated
+    // overload added for this issue forwards to from_bon8(ptr, ptr + len,
+    // ...) instead, like from_cbor's deprecated (ptr, len) overload does.
+    json result;
+    CHECK_NOTHROW(result = json::from_bon8(packed.data(), packed.size()));
+    CHECK(result == j);
+
+    // len must not collapse into the strict flag either
+    CHECK(json::from_bon8(packed.data(), packed.size(), false) == j);
+#endif
+}
+
 #ifdef JSON_HAS_CPP_17
 TEST_CASE("BON8 with std::byte")
 {
@@ -8,6 +8,14 @@

 #include "doctest_compatibility.h"

+// capture whether JSON_DELETE_DEPRECATED_FUNCTIONS was enabled on the command
+// line *before* including json.hpp, since the library #undefs it once the header
+// has been fully processed (see include/nlohmann/detail/macro_unscope.hpp); the
+// tests of deprecated functions are skipped if these functions are deleted
+#if defined(JSON_DELETE_DEPRECATED_FUNCTIONS) && (JSON_DELETE_DEPRECATED_FUNCTIONS == 1)
+    #define JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
+#endif
+
 #include <nlohmann/json.hpp>
 using nlohmann::json;

@@ -141,6 +149,54 @@ TEST_CASE("BSON")
            json const j = std::vector<int> {1, 2, 3, 4, 5, 6, 7};
            CHECK_THROWS_WITH_AS(json::to_bson(j), "[json.exception.type_error.317] to serialize to BSON, top-level type must be object, but is array", json::type_error&);
        }
+
+        SECTION("discarded")
+        {
+            json const j = json::value_t::discarded;
+            CHECK_THROWS_WITH_AS(json::to_bson(j), "[json.exception.type_error.317] to serialize to BSON, top-level type must be object, but is discarded", json::type_error&);
+        }
+    }
+
+    SECTION("discarded values nested in a container cannot be serialized to BSON")
+    {
+        json const discarded = json::value_t::discarded;
+
+        SECTION("as an object value")
+        {
+            json j;
+            j["a"] = 1;
+            j["b"] = discarded;
+#if JSON_DIAGNOSTICS
+            CHECK_THROWS_WITH_AS(json::to_bson(j), "[json.exception.type_error.321] (/b) cannot serialize discarded value to BSON", json::type_error&);
+#else
+            CHECK_THROWS_WITH_AS(json::to_bson(j), "[json.exception.type_error.321] cannot serialize discarded value to BSON", json::type_error&);
+#endif
+        }
+
+        SECTION("in an array that is an object value")
+        {
+            json j;
+            j["a"] = json::array({1, discarded, 2});
+#if JSON_DIAGNOSTICS
+            CHECK_THROWS_WITH_AS(json::to_bson(j), "[json.exception.type_error.321] (/a/1) cannot serialize discarded value to BSON", json::type_error&);
+#else
+            CHECK_THROWS_WITH_AS(json::to_bson(j), "[json.exception.type_error.321] cannot serialize discarded value to BSON", json::type_error&);
+#endif
+        }
+
+        SECTION("nested deeper (array in object in object)")
+        {
+            json inner_array = {1, discarded};
+            json middle_object;
+            middle_object["x"] = inner_array;
+            json j;
+            j["outer"] = middle_object;
+#if JSON_DIAGNOSTICS
+            CHECK_THROWS_WITH_AS(json::to_bson(j), "[json.exception.type_error.321] (/outer/x/1) cannot serialize discarded value to BSON", json::type_error&);
+#else
+            CHECK_THROWS_WITH_AS(json::to_bson(j), "[json.exception.type_error.321] cannot serialize discarded value to BSON", json::type_error&);
+#endif
+        }
    }

    SECTION("keys containing code-point U+0000 cannot be serialized to BSON")
@@ -1261,8 +1317,10 @@ TEST_CASE("BSON input that cannot be read is discarded by every overload")
    CHECK_THROWS_AS(_ = json::from_bson(input.begin(), input.end()), json::parse_error&);
    CHECK(json::from_bson(input, true, false).is_discarded());
    CHECK(json::from_bson(input.begin(), input.end(), true, false).is_discarded());
+#ifndef JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
    CHECK(json::from_bson(input.data(), input.size(), true, false).is_discarded());
    CHECK(json::from_bson({input.data(), input.size()}, true, false).is_discarded());
+#endif
 }

 TEST_CASE("BSON SAX parsing stops at every event")
@@ -1740,6 +1798,7 @@ TEST_CASE("BSON roundtrips" * doctest::skip())
                CHECK(j1 == j2);
            }

+#ifndef JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
            {
                INFO_WITH_TEMP(filename + ": uint8_t* and size");
                // parse JSON file
@@ -1754,6 +1813,7 @@ TEST_CASE("BSON roundtrips" * doctest::skip())
                // compare parsed JSON values
                CHECK(j1 == j2);
            }
+#endif

            {
                INFO_WITH_TEMP(filename + ": output to output adapters");
@@ -8,6 +8,14 @@

 #include "doctest_compatibility.h"

+// capture whether JSON_DELETE_DEPRECATED_FUNCTIONS was enabled on the command
+// line *before* including json.hpp, since the library #undefs it once the header
+// has been fully processed (see include/nlohmann/detail/macro_unscope.hpp); the
+// tests of deprecated functions are skipped if these functions are deleted
+#if defined(JSON_DELETE_DEPRECATED_FUNCTIONS) && (JSON_DELETE_DEPRECATED_FUNCTIONS == 1)
+    #define JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
+#endif
+
 #include <nlohmann/json.hpp>
 using nlohmann::json;

@@ -30,10 +38,49 @@ TEST_CASE("CBOR")
    {
        SECTION("discarded")
        {
-            // discarded values are not serialized
+            // a discarded value cannot be serialized to CBOR
            json const j = json::value_t::discarded;
-            const auto result = json::to_cbor(j);
-            CHECK(result.empty());
+            CHECK_THROWS_WITH_AS(json::to_cbor(j), "[json.exception.type_error.321] cannot serialize discarded value to CBOR", json::type_error&);
+        }
+
+        SECTION("discarded values nested in a container")
+        {
+            json const discarded = json::value_t::discarded;
+
+            SECTION("in an array")
+            {
+                json const j = {1, discarded, 2};
+#if JSON_DIAGNOSTICS
+                CHECK_THROWS_WITH_AS(json::to_cbor(j), "[json.exception.type_error.321] (/1) cannot serialize discarded value to CBOR", json::type_error&);
+#else
+                CHECK_THROWS_WITH_AS(json::to_cbor(j), "[json.exception.type_error.321] cannot serialize discarded value to CBOR", json::type_error&);
+#endif
+            }
+
+            SECTION("as an object value")
+            {
+                json j;
+                j["a"] = 1;
+                j["b"] = discarded;
+#if JSON_DIAGNOSTICS
+                CHECK_THROWS_WITH_AS(json::to_cbor(j), "[json.exception.type_error.321] (/b) cannot serialize discarded value to CBOR", json::type_error&);
+#else
+                CHECK_THROWS_WITH_AS(json::to_cbor(j), "[json.exception.type_error.321] cannot serialize discarded value to CBOR", json::type_error&);
+#endif
+            }
+
+            SECTION("nested deeper (array in object in array)")
+            {
+                json inner_array = {1, discarded};
+                json middle_object;
+                middle_object["x"] = inner_array;
+                json const j = {middle_object};
+#if JSON_DIAGNOSTICS
+                CHECK_THROWS_WITH_AS(json::to_cbor(j), "[json.exception.type_error.321] (/0/x/1) cannot serialize discarded value to CBOR", json::type_error&);
+#else
+                CHECK_THROWS_WITH_AS(json::to_cbor(j), "[json.exception.type_error.321] cannot serialize discarded value to CBOR", json::type_error&);
+#endif
+            }
        }

        SECTION("NaN")
@@ -2215,8 +2262,10 @@ TEST_CASE("CBOR input that cannot be read is discarded by every overload")
    CHECK_THROWS_AS(_ = json::from_cbor(input.begin(), input.end()), json::parse_error&);
    CHECK(json::from_cbor(input, true, false).is_discarded());
    CHECK(json::from_cbor(input.begin(), input.end(), true, false).is_discarded());
+#ifndef JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
    CHECK(json::from_cbor(input.data(), input.size(), true, false).is_discarded());
    CHECK(json::from_cbor({input.data(), input.size()}, true, false).is_discarded());
+#endif

    // a string that ends early, read through iterators that are not
    // contiguous and have to be copied from one element at a time
@@ -2613,12 +2662,14 @@ TEST_CASE("CBOR roundtrips" * doctest::skip())
                CHECK(j1 == j2);
            }

+#ifndef JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
            {
                INFO_WITH_TEMP(filename + ": uint8_t* and size");
                json j2;
                CHECK_NOTHROW(j2 = json::from_cbor({packed.data(), packed.size()}));
                CHECK(j1 == j2);
            }
+#endif

            {
                INFO_WITH_TEMP(filename + ": output to output adapters");
@@ -3185,7 +3236,8 @@ TEST_CASE("Tagged values")
        // CBOR encodes negative integers as: result = -1 - n
        // For type 0x3B, n is an 8-byte uint64_t. Valid range for n with
        // the default int64_t is [0, INT64_MAX], producing results in [INT64_MIN, -1].
-        // When n > INT64_MAX, the result exceeds int64_t range and is rejected.
+        // When n > INT64_MAX, the result exceeds int64_t range and is stored
+        // as a floating-point number, as the lexer does for JSON text.

        SECTION("n = 0 is valid (result = -1)")
        {
@@ -3206,33 +3258,34 @@ TEST_CASE("Tagged values")
            CHECK(result.get<int64_t>() == (std::numeric_limits<int64_t>::min)());
        }

-        SECTION("n = INT64_MAX + 1 is rejected (overflow)")
+        SECTION("n = INT64_MAX + 1 is stored as float")
        {
            // n = INT64_MAX + 1 (0x8000000000000000)
-            // result = -1 - n = -9223372036854775809, which exceeds int64_t range
+            // result = -1 - n = -9223372036854775809, which exceeds int64_t range;
+            // the nearest double is -9223372036854775808.0
            const std::vector<uint8_t> input = {0x3B, 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
-            json _;
-            CHECK_THROWS_WITH_AS(_ = json::from_cbor(input),
-                                 "[json.exception.parse_error.112] parse error at byte 9: syntax error while parsing CBOR value: negative integer overflow",
-                                 json::parse_error);
+            const auto result = json::from_cbor(input);
+            CHECK(result.is_number_float());
+            CHECK(result.get<double>() == -9223372036854775808.0);
+            CHECK(result == json::parse("-9223372036854775809"));
        }

-        SECTION("n = UINT64_MAX is rejected (overflow)")
+        SECTION("n = UINT64_MAX is stored as float")
        {
            // n = UINT64_MAX (0xFFFFFFFFFFFFFFFF)
            // result = -1 - n = -18446744073709551616, which exceeds int64_t range
            const std::vector<uint8_t> input = {0x3B, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF};
-            json _;
-            CHECK_THROWS_WITH_AS(_ = json::from_cbor(input),
-                                 "[json.exception.parse_error.112] parse error at byte 9: syntax error while parsing CBOR value: negative integer overflow",
-                                 json::parse_error);
+            const auto result = json::from_cbor(input);
+            CHECK(result.is_number_float());
+            CHECK(result.get<double>() == -18446744073709551616.0);
+            CHECK(result == json::parse("-18446744073709551616"));
        }

-        SECTION("overflow with allow_exceptions=false returns discarded")
+        SECTION("overflow with allow_exceptions=false is not an error")
        {
            const std::vector<uint8_t> input = {0x3B, 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
            const auto result = json::from_cbor(input, true, false);
-            CHECK(result.is_discarded());
+            CHECK(result.is_number_float());
        }
    }

@@ -13,15 +13,19 @@
 using nlohmann::json;

 #include <array> // array
-#include <cfloat> // FLT_EVAL_METHOD
 #include <cstdint> // uint32_t, uint64_t
+#include <cstdio> // snprintf
 #include <cstdlib> // strtod
 #include <cstring> // memcpy
+#include <map> // map
+#include <random> // mt19937
 #include <sstream> // stringstream
 #include <string> // string
 #include <utility> // pair
 #include <vector> // vector

+#include "float_hard_cases.hpp"
+
 namespace
 {
 // shortcut to scan a string literal
@@ -257,7 +261,7 @@ TEST_CASE("lexer number fast path")
            "123456789012345678901234567890",  // huge -> float
            "0.30000000000000004", "2.2250738585072014e-308", "1e308",
            // high-precision / wide-exponent values that exercise the
-            // std::from_chars (Eisel-Lemire) path beyond the Clinger subset
+            // Eisel-Lemire path beyond the Clinger subset
            "1.7976931348623157e308", "1.2345678901234567e-250",
            "9007199254740993", "5e-324", "1e-320"
        };
@@ -279,20 +283,18 @@ TEST_CASE("lexer number fast path")
        }
    }

-    SECTION("significant-digit gate for the Clinger fast path")
+    SECTION("significant digits around Clinger's fast path")
    {
-        // Clinger's fast path needs a significand below 2^53, so it cannot
-        // succeed once the mantissa has 17 or more significant digits (the
-        // significand would be at least 10^16). The lexer skips the attempt
-        // there. That is only allowed to save work: every value must still come
-        // out bit-exactly, and both scanners must agree. In particular the gate
-        // must not fire for tokens whose leading zeros merely look like extra
-        // digits - "0.1234567890123456" has 16 significant digits, not 17.
+        // Clinger's fast path needs a significand of at most 2^53, which
+        // tokens with 17 or more significant digits exceed. The conversion
+        // splits the token at the positions the scanners recorded, so leading
+        // zeros must not count as digits - "0.1234567890123456" has 16
+        // significant digits, not 17 - and both scanners must agree.
        const std::vector<std::string> numbers =
        {
            "1234567890123456",                  // 16 significant digits
-            "12345678901234567",                 // 17 -> attempt skipped
-            "123456789012345678",                // 18 -> attempt skipped
+            "12345678901234567",                 // 17
+            "123456789012345678",                // 18
            "0.1234567890123456",                // 16: the leading "0" is not significant
            "0.12345678901234567",               // 17
            "0.00000000000000001",               // 1, in a long token
@@ -663,46 +665,323 @@ TEST_CASE("lexer string fast path")
    }
 }

-TEST_CASE("parse_float_fast declines what it cannot convert exactly")
+TEST_CASE("lexer escape fast path")
 {
-    // The lexer only hands well-formed numbers to parse_float_fast, so the
-    // malformed ones below can only be passed to it directly. Declining is
-    // always safe: the caller then falls back to a slower, exact conversion.
-    const auto fast = [](const std::string & s, double & out)
+    // json::accept() never throws, so this section stays covered without
+    // exceptions; it pins which of the cases below are valid/invalid and
+    // checks the contiguous and streaming paths agree on that classification.
+    SECTION("accept() parity")
    {
-        return nlohmann::detail::parse_float_fast(s.data(), s.data() + s.size(), out);
+        const std::vector<std::pair<std::string, bool>> cases =
+        {
+            {"\\u0041", true}, {"\\u00e4", true}, {"\\u00E4", true},
+            {"\\uD83D\\uDE00", true},
+            {"\\u12", false}, {"\\u12G4", false}, {"\\uXYZW", false},
+            {"\\uD800", false}, {"\\uD800A", false}, {"\\uD800\\u0041", false},
+            {"\\uDC00", false}, {"\\u", false}
+        };
+
+        for (const auto& c : cases)
+        {
+            for (const std::size_t offset :
+                    {
+                        std::size_t{0}, std::size_t{9}
+                    })
+            {
+                const std::string doc = "[\"" + std::string(offset, 'a') + c.first + "\"]";
+                CAPTURE(doc)
+                CHECK(json::accept(doc) == c.second);
+                std::stringstream ss(doc);
+                CHECK(json::accept(ss) == c.second);
+            }
+        }
+    }
+
+#if !defined(JSON_NOEXCEPTION)
+    // the full outcome of parsing @a doc: the parsed value, or the exact
+    // error message, so a mismatch in either is caught
+    const auto outcome = [](const std::string & doc, bool streaming) -> std::string
+    {
+        try
+        {
+            if (streaming)
+            {
+                std::stringstream ss(doc);
+                const json j = json::parse(ss);
+                return j.dump();
+            }
+            const json j = json::parse(doc);
+            return j.dump();
+        }
+        catch (const json::exception& e)
+        {
+            return {e.what()};
+        }
    };
-    double out = 0;

-#if defined(FLT_EVAL_METHOD) && FLT_EVAL_METHOD != 0
-    // without true double precision, the fast path declines everything
-    CHECK_FALSE(fast("1.5", out));
-#else
-    CHECK(fast("1.5", out));
-    CHECK(out == 1.5);
-    CHECK(fast("+2.5e1", out));
-    CHECK(out == 25.0);
-    CHECK(fast("-25E-1", out));
-    CHECK(out == -2.5);
-    CHECK(fast("1e", out));
-    CHECK(out == 1.0);
+    SECTION("contiguous vs streaming parity")
+    {
+        const std::vector<std::string> escapes =
+        {
+            "\\u0041",             // "A"
+            "\\u00e4",             // "ä" (lowercase hex)
+            "\\u00E4",             // "ä" (uppercase hex)
+            "\\uD83D\\uDE00",      // valid surrogate pair (an emoji)
+            "\\u12",               // truncated: only 2 hex digits before the closing quote
+            "\\u12G4",             // invalid hex digit at the 3rd position
+            "\\uXYZW",             // all 4 bytes invalid
+            "\\uD800",             // lone high surrogate, string ends right after
+            "\\uD800A",            // high surrogate not followed by another \u escape
+            "\\uD800\\u0041",      // high surrogate followed by \u, but not a low surrogate
+            "\\uDC00",             // lone low surrogate
+            "\\u",                 // '\u' with nothing after (closing quote right away)
+        };
+
+        // once at the start of the string and once past the first 8-byte SWAR
+        // word of the outer string_bulk_run, so the escape is reached both
+        // right after the opening quote and mid-run
+        for (const auto& escape : escapes)
+        {
+            for (const std::size_t offset :
+                    {
+                        std::size_t{0}, std::size_t{9}
+                    })
+            {
+                const std::string doc = "[\"" + std::string(offset, 'a') + escape + "\"]";
+                CAPTURE(doc)
+                CHECK(outcome(doc, false) == outcome(doc, true));
+            }
+
+            // the escape is the last thing before end of input: no closing
+            // quote at all
+            const std::string truncated_doc = "[\"" + escape;
+            CAPTURE(truncated_doc)
+            CHECK(outcome(truncated_doc, false) == outcome(truncated_doc, true));
+        }
+    }
+
+    SECTION("truncated \\u escape at every distance from the end of input")
+    {
+        // ia.bulk_remaining() must correctly report fewer than 4 bytes for
+        // every possible count of trailing hex-looking bytes (0, 1, 2, or 3)
+        // before end of input, so the fast path declines and the byte path
+        // alone reports the "must be followed by 4 hex digits" error, at the
+        // same position, in every case
+        for (const std::string& tail :
+                {
+                    std::string{}, std::string("1"), std::string("12"), std::string("123")
+                })
+        {
+            const std::string doc = "[\"\\u" + tail;
+            CAPTURE(doc)
+            CHECK(outcome(doc, false) == outcome(doc, true));
+            CHECK(outcome(doc, false).find("must be followed by 4 hex digits") != std::string::npos);
+        }
+    }
+
+    SECTION("invalid hex digit at every position of the 4")
+    {
+        // the fast path must decline for *any* invalid byte among the 4, not
+        // just the first, and the byte path must then stop at exactly that
+        // position - same as it always has
+        for (std::size_t bad_pos = 0; bad_pos < 4; ++bad_pos)
+        {
+            std::string digits = "1234";
+            digits[bad_pos] = 'g'; // not a hex digit
+            const std::string doc = "[\"\\u" + digits + "\"]";
+            CAPTURE(doc)
+            CHECK(outcome(doc, false) == outcome(doc, true));
+            CHECK(outcome(doc, false).find("must be followed by 4 hex digits") != std::string::npos);
+        }
+    }
+
+    SECTION("random escapes")
+    {
+        // A seeded PRNG builds the 4 bytes following `\u` from a mix of hex
+        // digits and non-hex bytes, at varying distances from the start of
+        // the string, to compare the two scanners on many more shapes than
+        // are practical to enumerate by hand.
+        std::mt19937 gen(7654321); // NOLINT(cert-msc32-c,cert-msc51-cpp)
+        const std::string hex_alphabet = "0123456789AaBbCcDdEeFf";
+        std::uniform_int_distribution<std::size_t> pick_hex(0, hex_alphabet.size() - 1);
+        std::uniform_int_distribution<int> pick_byte(1, 255); // never NUL
+        std::uniform_int_distribution<int> pick_is_hex(0, 4); // 4-in-5 chance of a hex digit
+        std::uniform_int_distribution<std::size_t> pick_offset(0, 12);
+
+        std::vector<std::string> mismatches;
+        for (int iter = 0; iter < 3000; ++iter)
+        {
+            std::string digits;
+            for (int i = 0; i < 4; ++i)
+            {
+                if (pick_is_hex(gen) != 0)
+                {
+                    digits += hex_alphabet[pick_hex(gen)];
+                }
+                else
+                {
+                    char c = static_cast<char>(pick_byte(gen));
+                    if (c == '"' || c == '\\')
+                    {
+                        // keep the string well-formed apart from the escape
+                        // itself, so any mismatch is attributable to the \u
+                        // handling and not to an unrelated quote/escape
+                        c = 'z';
+                    }
+                    digits += c;
+                }
+            }
+            const std::string doc = "[\"" + std::string(pick_offset(gen), 'a') + "\\u" + digits + "\"]";
+            if (outcome(doc, false) != outcome(doc, true))
+            {
+                mismatches.push_back(doc);
+            }
+        }
+        CAPTURE(mismatches)
+        CHECK(mismatches.empty());
+    }
 #endif
+}

-    // not a number
-    CHECK_FALSE(fast("", out));
-    CHECK_FALSE(fast("-", out));
-    CHECK_FALSE(fast(".", out));
-    CHECK_FALSE(fast("1.2.3", out));
-    CHECK_FALSE(fast("1x", out));
-    CHECK_FALSE(fast("1e+", out));
-    CHECK_FALSE(fast("1e1x", out));
+namespace
+{
+// the index of the decimal point (or npos) and of the end of the mantissa of a
+// number token, which the lexer records while scanning it
+std::pair<std::size_t, std::size_t> float_token_layout(const std::string& s)
+{
+    std::size_t dot = std::string::npos;
+    std::size_t mantissa_end = s.size();
+    for (std::size_t i = 0; i < s.size(); ++i)
+    {
+        if (s[i] == '.')
+        {
+            dot = i;
+        }
+        else if (s[i] == 'e' || s[i] == 'E')
+        {
+            mantissa_end = i;
+            break;
+        }
+    }
+    return {dot, mantissa_end};
+}

-    // numbers that are not represented exactly on the fast path
-    CHECK_FALSE(fast("12345678901234567890", out));
-    CHECK_FALSE(fast("1e10000", out));
-    CHECK_FALSE(fast("9007199254740993", out));
-    CHECK_FALSE(fast("1e23", out));
-    CHECK_FALSE(fast("1e-23", out));
+template<typename FloatType>
+FloatType parse_native(const std::string& s)
+{
+    const auto layout = float_token_layout(s);
+    return nlohmann::detail::parse_float_native<FloatType>(s.data(), s.data() + s.size(), layout.first, layout.second);
+}
+
+std::uint64_t bits_of(double d)
+{
+    std::uint64_t b = 0;
+    std::memcpy(&b, &d, sizeof(b));
+    return b;
+}
+
+std::uint32_t bits_of(float f)
+{
+    std::uint32_t b = 0;
+    std::memcpy(&b, &f, sizeof(b));
+    return b;
+}
+
+std::uint64_t native_bits64(const std::string& s)
+{
+    return bits_of(parse_native<double>(s));
+}
+
+std::uint32_t native_bits32(const std::string& s)
+{
+    return bits_of(parse_native<float>(s));
+}
+} // namespace
+
+TEST_CASE("parse_float_native rounds correctly")
+{
+    SECTION("double")
+    {
+        CHECK(native_bits64("1.5") == 0x3FF8000000000000u);
+        CHECK(native_bits64("0.1") == 0x3FB999999999999Au);
+        CHECK(native_bits64("-0.0") == 0x8000000000000000u);
+        CHECK(native_bits64("0e999999999999999999999") == 0u);
+        // 2^53 + 1 is exactly between two doubles: ties to even, unless more digits follow
+        CHECK(native_bits64("9007199254740993") == 0x4340000000000000u);
+        CHECK(native_bits64("9007199254740993.0000000000000000001") == 0x4340000000000001u);
+        CHECK(native_bits64("9007199254740992.9999999999999999999") == 0x4340000000000000u);
+        // 1 + 2^-53 exactly (a tie), and one unit in the 55th digit around it
+        CHECK(native_bits64("1.00000000000000011102230246251565404236316680908203125") == 0x3FF0000000000000u);
+        CHECK(native_bits64("1.00000000000000011102230246251565404236316680908203126") == 0x3FF0000000000001u);
+        CHECK(native_bits64("1.00000000000000011102230246251565404236316680908203124") == 0x3FF0000000000000u);
+        // subnormal and overflow boundaries
+        CHECK(native_bits64("2.4703282292062327e-324") == 0u);
+        CHECK(native_bits64("2.4703282292062328e-324") == 1u);
+        CHECK(native_bits64("2.2250738585072011e-308") == 0x000FFFFFFFFFFFFFu);
+        CHECK(native_bits64("2.2250738585072012e-308") == 0x0010000000000000u);
+        CHECK(native_bits64("1.7976931348623157e308") == 0x7FEFFFFFFFFFFFFFu);
+        CHECK(native_bits64("1.7976931348623159e308") == 0x7FF0000000000000u);
+        CHECK(native_bits64("-1e400") == 0xFFF0000000000000u);
+        CHECK(native_bits64("-1e-400") == 0x8000000000000000u);
+        // exponents and zeros far beyond the range cancel out
+        CHECK(native_bits64("0." + std::string(1000, '0') + "1e1001") == 0x3FF0000000000000u);
+        CHECK(native_bits64("1" + std::string(1000, '0') + "e-1000") == 0x3FF0000000000000u);
+        CHECK(native_bits64("1e-99999999999999999999999") == 0u);
+        CHECK(native_bits64("1E+99999999999999999999999") == 0x7FF0000000000000u);
+        // more digits than any midpoint has (769): only whether a nonzero digit follows matters
+        const std::string tie = "1.00000000000000011102230246251565404236316680908203125";
+        CHECK(native_bits64(tie + std::string(800, '0')) == 0x3FF0000000000000u);
+        CHECK(native_bits64(tie + std::string(800, '0') + "1") == 0x3FF0000000000001u);
+    }
+
+    SECTION("float")
+    {
+        CHECK(native_bits32("1.5") == 0x3FC00000u);
+        CHECK(native_bits32("0.1") == 0x3DCCCCCDu);
+        CHECK(native_bits32("-0.0") == 0x80000000u);
+        // 2^24 + 1 is exactly between two floats
+        CHECK(native_bits32("16777217") == 0x4B800000u);
+        CHECK(native_bits32("16777217.000000000000000000001") == 0x4B800001u);
+        CHECK(native_bits32("16777218.999999999999999999999") == 0x4B800001u);
+        CHECK(native_bits32("16777219") == 0x4B800002u);
+        // subnormal and overflow boundaries
+        CHECK(native_bits32("3.4028235677973366e38") == 0x7F7FFFFFu);
+        CHECK(native_bits32("3.4028235677973367e38") == 0x7F800000u);
+        CHECK(native_bits32("7.006492321624085e-46") == 0u);
+        CHECK(native_bits32("7.006492321624086e-46") == 1u);
+        CHECK(native_bits32("1.1754942e-38") == 0x007FFFFFu);
+        CHECK(native_bits32("-1.17549435e-38") == 0x80800000u);
+        CHECK(native_bits32("1e39") == 0x7F800000u);
+        CHECK(native_bits32("-1e-50") == 0x80000000u);
+        // not rounded through double: its double would round to another float
+        CHECK(native_bits32("1.00000005960464477539062500000000001") == 0x3F800001u);
+        CHECK(native_bits32("9007199254740993") == 0x5A000000u);
+    }
+
+    SECTION("the conversion shared with other parsers")
+    {
+        // convert_float() gives the lexer's results, for every type
+        const std::vector<std::string> tokens =
+        {
+            "0", "-0.0", "1.5", "0.1", "1e-400", "-2.5E+3", "123456789012345678901234567890",
+            "9007199254740993.0000000000000000001", "4.9406564584124654e-324"
+        };
+        using float_json = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t, float>;
+        using long_double_json = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t, long double>;
+        for (const auto& t : tokens)
+        {
+            CAPTURE(t)
+            const auto layout = float_token_layout(t);
+            const char* const first = t.data();
+            const char* const last = first + t.size();
+            const auto d = nlohmann::detail::convert_float<double>(first, last, layout.first, layout.second);
+            const auto f = nlohmann::detail::convert_float<float>(first, last, layout.first, layout.second);
+            const auto ld = nlohmann::detail::convert_float<long double>(first, last, layout.first, layout.second);
+            CHECK(bits_of(d) == bits_of(json::parse(t).get<double>()));
+            CHECK(bits_of(f) == bits_of(float_json::parse(t).get<float>()));
+            CHECK(ld == long_double_json::parse(t).get<long double>());
+        }
+    }
 }

 namespace
@@ -806,40 +1085,6 @@ std::size_t big_bit_length(const big_uint& a)
    }
    return n;
 }
-
-std::uint64_t bits_of(double d)
-{
-    std::uint64_t b = 0;
-    std::memcpy(&b, &d, sizeof(b));
-    return b;
-}
-
-bool eisel_lemire(const std::string& s, double& out)
-{
-    return nlohmann::detail::parse_float_eisel_lemire(s.data(), s.data() + s.size(), out);
-}
-
-// significant digits of a token, without trailing zeros
-std::size_t significant_digits(const std::string& s)
-{
-    std::string digits;
-    for (const char c : s)
-    {
-        if (c == 'e' || c == 'E')
-        {
-            break;
-        }
-        if (c >= '0' && c <= '9' && !(digits.empty() && c == '0'))
-        {
-            digits += c;
-        }
-    }
-    while (!digits.empty() && digits.back() == '0')
-    {
-        digits.pop_back();
-    }
-    return digits.size();
-}
 } // namespace

 TEST_CASE("Eisel-Lemire float conversion")
@@ -1237,26 +1482,33 @@ TEST_CASE("Eisel-Lemire float conversion")
        for (const auto& c : known)
        {
            CAPTURE(c.first)
-            double out = 0;
-            if (eisel_lemire(c.first, out))
-            {
-                CHECK(bits_of(out) == c.second);
-            }
-            else
-            {
-                // only tokens with more than 19 significant digits are left to
-                // strtod: those whose value lies too close to a tie
-                CHECK(significant_digits(c.first) > 19);
-            }
+            CHECK(native_bits64(c.first) == c.second);
        }
    }

+    SECTION("binary32")
+    {
+        using binary32 = nlohmann::detail::ieee_binary_format<24>;
+        CHECK(nlohmann::detail::eisel_lemire<binary32>(0, 1) == 0x3F800000u);
+        CHECK(nlohmann::detail::eisel_lemire<binary32>(-1, 1) == 0x3DCCCCCDu);
+        CHECK(nlohmann::detail::eisel_lemire<binary32>(-1, 15) == 0x3FC00000u);
+        CHECK(nlohmann::detail::eisel_lemire<binary32>(0, 16777217) == 0x4B800000u); // tie, to even
+        CHECK(nlohmann::detail::eisel_lemire<binary32>(0, 16777219) == 0x4B800002u); // tie, to even
+        CHECK(nlohmann::detail::eisel_lemire<binary32>(-45, 1) == 0x00000001u);
+        CHECK(nlohmann::detail::eisel_lemire<binary32>(-46, 7) == 0x00000000u);
+        CHECK(nlohmann::detail::eisel_lemire<binary32>(-46, 8) == 0x00000001u);
+        CHECK(nlohmann::detail::eisel_lemire<binary32>(-65, 9999999999999999999u) == 0x00000000u);
+        CHECK(nlohmann::detail::eisel_lemire<binary32>(20, 3402823466385288598u) == 0x7F7FFFFFu);
+        CHECK(nlohmann::detail::eisel_lemire<binary32>(20, 3402823669209384635u) == 0x7F800000u);
+        CHECK(nlohmann::detail::eisel_lemire<binary32>(39, 1) == 0x7F800000u);
+        CHECK(nlohmann::detail::eisel_lemire<binary32>(-5, 0) == 0x00000000u);
+    }
+
    SECTION("round trip")
    {
-        // every double written by to_chars and read back, also with trailing
-        // digits that make the token longer than 19 digits
+        // every double written by to_chars and read back, and its 17-digit
+        // form with trailing digits that make the token longer than 19 digits
        std::uint64_t state = 5295;
-        std::size_t declined = 0;
        for (int i = 0; i < 200000; ++i)
        {
            state ^= state << 13u;
@@ -1278,30 +1530,51 @@ TEST_CASE("Eisel-Lemire float conversion")
            const char* end = nlohmann::detail::to_chars(buffer.data(), buffer.data() + buffer.size(), d);
            const std::string token(buffer.data(), static_cast<std::size_t>(end - buffer.data()));
            CAPTURE(token)
-            double out = 0;
-            REQUIRE(eisel_lemire(token, out));
-            CHECK(bits_of(out) == b);
+            CHECK(native_bits64(token) == b);

-            // insert digits before the exponent: the value moves by far less
-            // than the distance to the rounding boundary, so it must not change
-            std::string longer = token;
+            // insert digits before the exponent of the 17-digit form: that
+            // form lies strictly inside the rounding interval of the double
+            // (the shortest one may lie on its boundary), and the digits move
+            // it by far less than the distance to the boundary, so the value
+            // must not change
+            std::array<char, 64> digits17{};
+            static_cast<void>(std::snprintf(digits17.data(), digits17.size(), "%.17g", d)); // NOLINT(cppcoreguidelines-pro-type-vararg,hicpp-vararg)
+            std::string longer = digits17.data();
            const std::size_t e = longer.find('e');
            const std::size_t dot = longer.find('.');
            const std::string extra = dot == std::string::npos ? ".000000000000000000001" : "000000000000000000001";
            longer.insert(e == std::string::npos ? longer.size() : e, extra);
            CAPTURE(longer)
-            if (eisel_lemire(longer, out))
+            CHECK(native_bits64(longer) == b);
+        }
+    }
+
+    SECTION("round trip, binary32")
+    {
+        std::uint32_t state = 5295;
+        for (int i = 0; i < 100000; ++i)
+        {
+            state ^= state << 13u;
+            state ^= state >> 17u;
+            state ^= state << 5u;
+            std::uint32_t b = state;
+            if ((b & 0x7F800000u) == 0x7F800000u)
            {
-                CHECK(bits_of(out) == b);
+                continue; // infinity or NaN
            }
-            else
+            if (i % 4 == 0)
            {
-                // w and w + 1 round differently: only when the value is very
-                // close to a rounding boundary
-                ++declined;
+                b &= 0x807FFFFFu; // subnormals
            }
+            float f = 0;
+            std::memcpy(&f, &b, sizeof(f));
+
+            std::array<char, 64> buffer{};
+            const char* end = nlohmann::detail::to_chars(buffer.data(), buffer.data() + buffer.size(), f);
+            const std::string token(buffer.data(), static_cast<std::size_t>(end - buffer.data()));
+            CAPTURE(token)
+            CHECK(native_bits32(token) == b);
        }
-        CHECK(declined < 1000); // 107 of the 200,000
    }

    SECTION("used by the lexer")
@@ -1315,3 +1588,177 @@ TEST_CASE("Eisel-Lemire float conversion")
                             "[json.exception.out_of_range.406] number overflow parsing '1.7976931348623159e308'", json::out_of_range&);
    }
 }
+
+namespace
+{
+using float_json = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t, float>;
+
+// the bits of the float that parse() gives for a token, via both scanners;
+// the value must be the same for both
+template<typename Json, typename Bits>
+void check_parse(const std::string& token, Bits expected, Bits infinity)
+{
+    std::stringstream stream(token);
+    if ((expected & ~(Bits{1} << (8 * sizeof(Bits) - 1))) == infinity)
+    {
+        Json _;
+        CHECK_THROWS_WITH_AS(_ = Json::parse(token), ("[json.exception.out_of_range.406] number overflow parsing '" + token + "'").c_str(), typename Json::out_of_range&);
+        CHECK_THROWS_WITH_AS(_ = Json::parse(stream), ("[json.exception.out_of_range.406] number overflow parsing '" + token + "'").c_str(), typename Json::out_of_range&);
+        return;
+    }
+    const Json contiguous = Json::parse(token);
+    const Json streamed = Json::parse(stream);
+    if (contiguous.is_number_float()) // not an integer that fits
+    {
+        CHECK(bits_of(contiguous.template get<typename Json::number_float_t>()) == expected);
+        CHECK(bits_of(streamed.template get<typename Json::number_float_t>()) == expected);
+    }
+    else
+    {
+        CHECK(streamed.is_number_integer());
+    }
+}
+} // namespace
+
+TEST_CASE("float conversion of hard cases")
+{
+    // see float_hard_cases.hpp
+    for (const auto& c : float_hard_cases::cases())
+    {
+        const std::string token = c.token;
+        CAPTURE(token)
+        CHECK(native_bits64(token) == c.bits64);
+        CHECK(native_bits32(token) == c.bits32);
+        check_parse<json>(token, c.bits64, std::uint64_t{0x7FF0000000000000u});
+        check_parse<float_json>(token, c.bits32, std::uint32_t{0x7F800000u});
+    }
+}
+
+TEST_CASE("float overflow and underflow in the parser")
+{
+    SECTION("double")
+    {
+        check_parse<json>("1.7976931348623157e308", std::uint64_t{0x7FEFFFFFFFFFFFFFu}, std::uint64_t{0x7FF0000000000000u});
+        check_parse<json>("1.7976931348623159e308", std::uint64_t{0x7FF0000000000000u}, std::uint64_t{0x7FF0000000000000u});
+        check_parse<json>("-1e309", std::uint64_t{0xFFF0000000000000u}, std::uint64_t{0x7FF0000000000000u});
+        check_parse<json>("1" + std::string(400, '0'), std::uint64_t{0x7FF0000000000000u}, std::uint64_t{0x7FF0000000000000u});
+        check_parse<json>("1e99999999999999999999", std::uint64_t{0x7FF0000000000000u}, std::uint64_t{0x7FF0000000000000u});
+        // an underflow gives a zero with the sign of the token
+        check_parse<json>("1e-400", std::uint64_t{0}, std::uint64_t{0x7FF0000000000000u});
+        check_parse<json>("-1e-400", std::uint64_t{0x8000000000000000u}, std::uint64_t{0x7FF0000000000000u});
+        check_parse<json>("-2.4703282292062327e-324", std::uint64_t{0x8000000000000000u}, std::uint64_t{0x7FF0000000000000u});
+        check_parse<json>("0." + std::string(400, '0') + "1", std::uint64_t{0}, std::uint64_t{0x7FF0000000000000u});
+    }
+
+    SECTION("float")
+    {
+        check_parse<float_json>("3.4028234e38", std::uint32_t{0x7F7FFFFFu}, std::uint32_t{0x7F800000u});
+        check_parse<float_json>("3.4028236e38", std::uint32_t{0x7F800000u}, std::uint32_t{0x7F800000u});
+        check_parse<float_json>("-1e39", std::uint32_t{0xFF800000u}, std::uint32_t{0x7F800000u});
+        check_parse<float_json>("1e-46", std::uint32_t{0}, std::uint32_t{0x7F800000u});
+        check_parse<float_json>("-1e-46", std::uint32_t{0x80000000u}, std::uint32_t{0x7F800000u});
+        check_parse<float_json>("-7.006492321624085e-46", std::uint32_t{0x80000000u}, std::uint32_t{0x7F800000u});
+        check_parse<float_json>("-7.006492321624086e-46", std::uint32_t{0x80000001u}, std::uint32_t{0x7F800000u});
+    }
+}
+
+TEST_CASE("string scanning kernels")
+{
+    // the word-at-a-time kernels must stop exactly where a byte-by-byte scan
+    // stops, for any content, length, and alignment
+    const auto reference_special = [](const unsigned char* data, std::size_t n)
+    {
+        std::size_t i = 0;
+        while (i < n && !nlohmann::detail::is_string_special(data[i]))
+        {
+            ++i;
+        }
+        return i;
+    };
+    const auto reference_copyable = [](const unsigned char* data, std::size_t n)
+    {
+        std::size_t i = 0;
+        while (i < n && nlohmann::detail::is_ascii_copyable(data[i]))
+        {
+            ++i;
+        }
+        return i;
+    };
+    const auto reference_bulk_run = [](const unsigned char* data, std::size_t n)
+    {
+        std::size_t i = 0;
+        while (i < n)
+        {
+            if (data[i] < 0x80u)
+            {
+                if (nlohmann::detail::is_string_special(data[i]))
+                {
+                    break;
+                }
+                ++i;
+                continue;
+            }
+            const std::size_t seq = nlohmann::detail::validate_one_utf8(data + i, n - i);
+            if (seq == 0)
+            {
+                break;
+            }
+            i += seq;
+        }
+        return i;
+    };
+
+    // pieces: ordinary ASCII, stops, DEL, well-formed sequences of every
+    // length, and ill-formed or truncated ones
+    const std::vector<std::string> pieces =
+    {
+        "a", "Z", " ", "~", "0123456789", "\"", "\\", std::string(1, '\0'), "\n", "\x1F", "\x7F",
+        "\xC3\xA4", "\xE2\x82\xAC", "\xE6\x97\xA5\xE6\x9C\xAC", "\xF0\x9F\x98\x80", "\xED\x9F\xBF",
+        "\x80", "\xC0\x80", "\xC3", "\xE2\x82", "\xED\xA0\x80", "\xF4\x90\x80\x80", "\xFF",
+    };
+    std::uint64_t state = 5295;
+    const auto next = [&state]()
+    {
+        state ^= state << 13u;
+        state ^= state >> 7u;
+        state ^= state << 17u;
+        return state;
+    };
+    // the upper half as a 32-bit value: converts to std::size_t implicitly on
+    // every platform (a cast of std::uint64_t is useless where both are the
+    // same type, and required where std::size_t is 32 bits wide)
+    const auto next_small = [&next]()
+    {
+        return static_cast<std::uint32_t>(next() >> 32u);
+    };
+    for (int round = 0; round < 100000; ++round)
+    {
+        // mostly ordinary text, so that runs span several words
+        std::string text(next_small() % 8u, '.');
+        const std::size_t count = next_small() % 12u;
+        for (std::size_t k = 0; k < count; ++k)
+        {
+            const std::size_t p = (next() % 4 == 0) ? next_small() % pieces.size() : 0;
+            text += pieces[p];
+            text += std::string(next_small() % 10u, 'x');
+        }
+        const auto* data = reinterpret_cast<const unsigned char*>(text.data()); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+        for (std::size_t offset = 0; offset < 3 && offset <= text.size(); ++offset)
+        {
+            const std::size_t n = text.size() - offset;
+            CAPTURE(text)
+            CAPTURE(offset)
+            CHECK(nlohmann::detail::find_string_special(data + offset, n) == reference_special(data + offset, n));
+            CHECK(nlohmann::detail::find_ascii_copyable_run(data + offset, n) == reference_copyable(data + offset, n));
+            CHECK(nlohmann::detail::scalar_string_bulk_run(data + offset, n) == reference_bulk_run(data + offset, n));
+        }
+    }
+
+    // the trailing-zero count, whichever implementation the compiler gets
+    for (int k = 0; k < 64; ++k)
+    {
+        const std::uint64_t bit = std::uint64_t{1} << k;
+        CHECK(nlohmann::detail::count_trailing_zeros(bit) == k);
+        CHECK(nlohmann::detail::count_trailing_zeros(bit | (bit << 1u) | 0x8000000000000000u) == k);
+    }
+}
@@ -2317,6 +2317,58 @@ TEST_CASE("parser class")
 #endif
    }

+    SECTION("comments before separators")
+    {
+        // The parser first checks for the expected ':' or ',' and only then
+        // falls back to the full token switch, which skips comments. A comment
+        // directly before a separator takes that fallback.
+        json _;
+
+        SECTION("ignored")
+        {
+            const std::vector<std::pair<std::string, json>> inputs =
+            {
+                {"{\"a\" /* c */ : 1}", {{"a", 1}}},
+                {"{\"a\" // c\n: 1}", {{"a", 1}}},
+                {R"({"a": 1, "b" /* c */ : 2})", {{"a", 1}, {"b", 2}}},
+                {R"({"a": 1 /* c */ , "b": 2})", {{"a", 1}, {"b", 2}}},
+                {"{\"a\": 1 // c\n, \"b\": 2}", {{"a", 1}, {"b", 2}}},
+                {"[1 /* c */ , 2]", {1, 2}},
+                {"[1 // c\n, 2]", {1, 2}},
+                {"{\"a\" /* c */ /* d */ : [1 // c\n , 2 /**/ ] /**/ , \"b\" : 3}", {{"a", {1, 2}}, {"b", 3}}}
+            };
+            for (const auto& input : inputs)
+            {
+                CAPTURE(input.first)
+                CHECK(json::parse(input.first, nullptr, true, true) == input.second);
+                CHECK(json::accept(input.first, true));
+            }
+        }
+
+        SECTION("ignored, with trailing commas")
+        {
+            CHECK(json::parse(std::string("[1 /* c */ , ]"), nullptr, true, true, true) == json({1}));
+            CHECK(json::parse(std::string("{\"a\": 1 /* c */ , }"), nullptr, true, true, true) == json({{"a", 1}}));
+            CHECK_THROWS_WITH_AS(_ = json::parse(std::string("[1 /* c */ , ]"), nullptr, true, true),
+                                 "[json.exception.parse_error.101] parse error at line 1, column 14: syntax error while parsing value - unexpected ']'; expected '[', '{', or a literal", json::parse_error);
+            CHECK_THROWS_WITH_AS(_ = json::parse(std::string("{\"a\": 1 /* c */ , }"), nullptr, true, true),
+                                 "[json.exception.parse_error.101] parse error at line 1, column 19: syntax error while parsing object key - unexpected '}'; expected string literal", json::parse_error);
+        }
+
+        SECTION("not ignored")
+        {
+            CHECK_THROWS_WITH_AS(_ = json::parse(std::string("{\"a\" /* c */ : 1}")),
+                                 "[json.exception.parse_error.101] parse error at line 1, column 6: syntax error while parsing object separator - invalid literal; last read: '\"a\" /'; expected ':'", json::parse_error);
+            CHECK_THROWS_WITH_AS(_ = json::parse(std::string("{\"a\": 1, \"b\" /* c */ : 2}")),
+                                 "[json.exception.parse_error.101] parse error at line 1, column 14: syntax error while parsing object separator - invalid literal; last read: '\"b\" /'; expected ':'", json::parse_error);
+            CHECK_THROWS_WITH_AS(_ = json::parse(std::string("{\"a\": 1 /* c */ , \"b\": 2}")),
+                                 "[json.exception.parse_error.101] parse error at line 1, column 9: syntax error while parsing object - invalid literal; last read: '1 /'; expected '}'", json::parse_error);
+            CHECK_THROWS_WITH_AS(_ = json::parse(std::string("[1 /* c */ , 2]")),
+                                 "[json.exception.parse_error.101] parse error at line 1, column 4: syntax error while parsing array - invalid literal; last read: '1 /'; expected ']'", json::parse_error);
+            CHECK(!json::accept(std::string("[1 /* c */ , 2]")));
+        }
+    }
+
 #if JSON_DIAGNOSTIC_POSITIONS
    // Macro for all test cases for start_pos and end_pos
 #define SETUP_TESTCASES() \
@@ -191,8 +191,10 @@ TEST_CASE("value conversion")
    {
        enum class bool_enum : bool { off, on };

-        CHECK(json(bool_enum::off).get<bool_enum>() == bool_enum::off);
-        CHECK(json(bool_enum::on).get<bool_enum>() == bool_enum::on);
+        // the extra parentheses keep doctest from printing the enum via its
+        // underlying type, which MSVC 2015 reports as C4800
+        CHECK((json(bool_enum::off).get<bool_enum>() == bool_enum::off));
+        CHECK((json(bool_enum::on).get<bool_enum>() == bool_enum::on));
    }
 #endif

@@ -851,8 +853,11 @@ TEST_CASE("std::optional")
        CHECK_THROWS_WITH_AS(json(opt), "cannot serialize throwing_to_json_type", std::runtime_error&);

        // the conversion is noexcept exactly when converting the contained value is
+        // (except with MSVC 2017, where it is never noexcept, see to_json.hpp)
+#if !defined(_MSC_VER) || defined(__clang__) || _MSC_VER >= 1920
        static_assert(!std::is_nothrow_constructible<json, const std::optional<throwing_to_json_type>&>::value);
        static_assert(std::is_nothrow_constructible<json, const std::optional<int>&>::value);
+#endif
    }
 #endif
 }
@@ -0,0 +1,229 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#include "doctest_compatibility.h"
+
+// This file tests the opt-in JSON_DELETE_DEPRECATED_FUNCTIONS, so it defines the
+// macro itself instead of relying on the build configuration.
+#ifdef JSON_DELETE_DEPRECATED_FUNCTIONS
+    #undef JSON_DELETE_DEPRECATED_FUNCTIONS
+#endif
+#define JSON_DELETE_DEPRECATED_FUNCTIONS 1
+
+#include <nlohmann/json.hpp>
+using nlohmann::json;
+
+#include <cstddef>
+#include <cstdint>
+#include <istream>
+#include <ostream>
+#include <sstream>
+#include <string>
+#include <type_traits>
+#include <utility>
+
+namespace
+{
+template<typename...>
+struct make_void
+{
+    using type = void;
+};
+
+template<typename... Ts>
+using void_t = typename make_void<Ts...>::type;
+
+// A deleted function is still found by overload resolution, but naming it in an
+// unevaluated operand is ill-formed, so each of the following traits is false
+// exactly if the expression selects a deleted (or no) function.
+#define JSON_TEST_DETECT(name, expr)                                 \
+    template<typename J, typename = void>                            \
+    struct name : std::false_type {};                                \
+    template<typename J>                                             \
+    struct name<J, void_t<decltype(expr)>> : std::true_type {}
+
+using ptr_t = const std::uint8_t*;
+
+JSON_TEST_DETECT(from_cbor_ptr_len, J::from_cbor(std::declval<ptr_t>(), std::declval<std::size_t>()));
+JSON_TEST_DETECT(from_msgpack_ptr_len, J::from_msgpack(std::declval<ptr_t>(), std::declval<std::size_t>()));
+JSON_TEST_DETECT(from_ubjson_ptr_len, J::from_ubjson(std::declval<ptr_t>(), std::declval<std::size_t>()));
+JSON_TEST_DETECT(from_bjdata_ptr_len, J::from_bjdata(std::declval<ptr_t>(), std::declval<std::size_t>()));
+JSON_TEST_DETECT(from_bon8_ptr_len, J::from_bon8(std::declval<ptr_t>(), std::declval<std::size_t>()));
+JSON_TEST_DETECT(from_bson_ptr_len, J::from_bson(std::declval<ptr_t>(), std::declval<std::size_t>()));
+
+JSON_TEST_DETECT(from_cbor_ptr_ptr, J::from_cbor(std::declval<ptr_t>(), std::declval<ptr_t>()));
+JSON_TEST_DETECT(from_msgpack_ptr_ptr, J::from_msgpack(std::declval<ptr_t>(), std::declval<ptr_t>()));
+JSON_TEST_DETECT(from_ubjson_ptr_ptr, J::from_ubjson(std::declval<ptr_t>(), std::declval<ptr_t>()));
+JSON_TEST_DETECT(from_bjdata_ptr_ptr, J::from_bjdata(std::declval<ptr_t>(), std::declval<ptr_t>()));
+JSON_TEST_DETECT(from_bon8_ptr_ptr, J::from_bon8(std::declval<ptr_t>(), std::declval<ptr_t>()));
+JSON_TEST_DETECT(from_bson_ptr_ptr, J::from_bson(std::declval<ptr_t>(), std::declval<ptr_t>()));
+
+JSON_TEST_DETECT(from_cbor_init_list, J::from_cbor({std::declval<ptr_t>(), std::declval<std::size_t>()}));
+JSON_TEST_DETECT(from_msgpack_init_list, J::from_msgpack({std::declval<ptr_t>(), std::declval<std::size_t>()}));
+JSON_TEST_DETECT(from_ubjson_init_list, J::from_ubjson({std::declval<ptr_t>(), std::declval<std::size_t>()}));
+JSON_TEST_DETECT(from_bson_init_list, J::from_bson({std::declval<ptr_t>(), std::declval<std::size_t>()}));
+
+JSON_TEST_DETECT(parse_init_list, J::parse({std::declval<ptr_t>(), std::declval<std::size_t>()}));
+JSON_TEST_DETECT(accept_init_list, J::accept({std::declval<ptr_t>(), std::declval<std::size_t>()}));
+JSON_TEST_DETECT(sax_parse_init_list, J::sax_parse({std::declval<ptr_t>(), std::declval<std::size_t>()}, std::declval<nlohmann::json_sax<J>*>()));
+JSON_TEST_DETECT(parse_ptr_ptr, J::parse(std::declval<ptr_t>(), std::declval<ptr_t>()));
+
+JSON_TEST_DETECT(iterator_wrapper, J::iterator_wrapper(std::declval<J&>()));
+JSON_TEST_DETECT(iterator_wrapper_const, J::iterator_wrapper(std::declval<const J&>()));
+JSON_TEST_DETECT(items, std::declval<J&>().items());
+
+JSON_TEST_DETECT(json_ltlt_istream, std::declval<J&>() << std::declval<std::istream&>());
+JSON_TEST_DETECT(istream_gtgt_json, std::declval<std::istream&>() >> std::declval<J&>());
+JSON_TEST_DETECT(json_gtgt_ostream, std::declval<const J&>() >> std::declval<std::ostream&>());
+JSON_TEST_DETECT(ostream_ltlt_json, std::declval<std::ostream&>() << std::declval<const J&>());
+
+JSON_TEST_DETECT(ptr_eq_ptr, std::declval<const typename J::json_pointer&>() == std::declval<const typename J::json_pointer&>());
+JSON_TEST_DETECT(ptr_ne_ptr, std::declval<const typename J::json_pointer&>() != std::declval<const typename J::json_pointer&>());
+JSON_TEST_DETECT(ptr_eq_string, std::declval<const typename J::json_pointer&>() == std::declval<const std::string&>());
+JSON_TEST_DETECT(string_eq_ptr, std::declval<const std::string&>() == std::declval<const typename J::json_pointer&>());
+JSON_TEST_DETECT(ptr_eq_c_string, std::declval<const typename J::json_pointer&>() == std::declval<const char*>());
+JSON_TEST_DETECT(c_string_eq_ptr, std::declval<const char*>() == std::declval<const typename J::json_pointer&>());
+JSON_TEST_DETECT(ptr_ne_string, std::declval<const typename J::json_pointer&>() != std::declval<const std::string&>());
+JSON_TEST_DETECT(string_ne_ptr, std::declval<const std::string&>() != std::declval<const typename J::json_pointer&>());
+JSON_TEST_DETECT(ptr_to_string, std::declval<const typename J::json_pointer&>().to_string());
+
+// json_pointer with a basic_json type as template argument
+template<typename J>
+using legacy_ptr_t = const nlohmann::json_pointer<J>& ;
+JSON_TEST_DETECT(legacy_ptr_value, std::declval<const J&>().value(std::declval<legacy_ptr_t<J>>(), 0));
+JSON_TEST_DETECT(legacy_ptr_value_rvalue, std::declval<const J&>().value(std::declval<legacy_ptr_t<J>>(), std::string()));
+JSON_TEST_DETECT(legacy_ptr_contains, std::declval<const J&>().contains(std::declval<legacy_ptr_t<J>>()));
+JSON_TEST_DETECT(legacy_ptr_subscript, std::declval<J&>()[std::declval<legacy_ptr_t<J>>()]);
+JSON_TEST_DETECT(legacy_ptr_subscript_const, std::declval<const J&>()[std::declval<legacy_ptr_t<J>>()]);
+JSON_TEST_DETECT(legacy_ptr_at, std::declval<J&>().at(std::declval<legacy_ptr_t<J>>()));
+JSON_TEST_DETECT(legacy_ptr_at_const, std::declval<const J&>().at(std::declval<legacy_ptr_t<J>>()));
+JSON_TEST_DETECT(ptr_value, std::declval<const J&>().value(std::declval<const typename J::json_pointer&>(), 0));
+JSON_TEST_DETECT(ptr_at, std::declval<J&>().at(std::declval<const typename J::json_pointer&>()));
+
+#undef JSON_TEST_DETECT
+} // namespace
+
+TEST_CASE("JSON_DELETE_DEPRECATED_FUNCTIONS")
+{
+    // MSVC 2015 does not treat selecting a deleted function in decltype as a
+    // substitution failure, so the traits cannot tell deleted functions apart
+    // there; calling them still fails to compile
+#if !(defined(_MSC_VER) && _MSC_VER < 1910)
+    SECTION("from_* with a pointer and a length")
+    {
+        // the overloads are deleted rather than removed, so the length cannot
+        // silently bind to the strict parameter of from_*(InputType&&, bool)
+        CHECK_FALSE(from_cbor_ptr_len<json>::value);
+        CHECK_FALSE(from_msgpack_ptr_len<json>::value);
+        CHECK_FALSE(from_ubjson_ptr_len<json>::value);
+        CHECK_FALSE(from_bjdata_ptr_len<json>::value);
+        CHECK_FALSE(from_bon8_ptr_len<json>::value);
+        CHECK_FALSE(from_bson_ptr_len<json>::value);
+
+        // the replacement
+        CHECK(from_cbor_ptr_ptr<json>::value);
+        CHECK(from_msgpack_ptr_ptr<json>::value);
+        CHECK(from_ubjson_ptr_ptr<json>::value);
+        CHECK(from_bjdata_ptr_ptr<json>::value);
+        CHECK(from_bon8_ptr_ptr<json>::value);
+        CHECK(from_bson_ptr_ptr<json>::value);
+    }
+
+    SECTION("initializer lists of a pointer and a length")
+    {
+        CHECK_FALSE(from_cbor_init_list<json>::value);
+        CHECK_FALSE(from_msgpack_init_list<json>::value);
+        CHECK_FALSE(from_ubjson_init_list<json>::value);
+        CHECK_FALSE(from_bson_init_list<json>::value);
+        CHECK_FALSE(parse_init_list<json>::value);
+        CHECK_FALSE(accept_init_list<json>::value);
+        CHECK_FALSE(sax_parse_init_list<json>::value);
+
+        // the replacement
+        CHECK(parse_ptr_ptr<json>::value);
+    }
+
+    SECTION("iterator_wrapper")
+    {
+        CHECK_FALSE(iterator_wrapper<json>::value);
+        CHECK_FALSE(iterator_wrapper_const<json>::value);
+
+        // the replacement
+        CHECK(items<json>::value);
+    }
+
+    SECTION("stream operators with reversed operands")
+    {
+        CHECK_FALSE(json_ltlt_istream<json>::value);
+        CHECK_FALSE(json_gtgt_ostream<json>::value);
+
+        // the replacement
+        CHECK(istream_gtgt_json<json>::value);
+        CHECK(ostream_ltlt_json<json>::value);
+    }
+
+    SECTION("json_pointer")
+    {
+        // conversion to a string
+        CHECK_FALSE(std::is_constructible<std::string, json::json_pointer>::value);
+        CHECK_FALSE(std::is_convertible<json::json_pointer, std::string>::value);
+
+        // comparison with a string
+        CHECK_FALSE(ptr_eq_string<json>::value);
+        CHECK_FALSE(string_eq_ptr<json>::value);
+        CHECK_FALSE(ptr_eq_c_string<json>::value);
+        CHECK_FALSE(c_string_eq_ptr<json>::value);
+        CHECK_FALSE(ptr_ne_string<json>::value);
+        CHECK_FALSE(string_ne_ptr<json>::value);
+
+        // the replacement
+        CHECK(ptr_to_string<json>::value);
+        CHECK(ptr_eq_ptr<json>::value);
+        CHECK(ptr_ne_ptr<json>::value);
+    }
+
+    SECTION("json_pointer with a basic_json type as template argument")
+    {
+        CHECK_FALSE(legacy_ptr_value<json>::value);
+        CHECK_FALSE(legacy_ptr_value_rvalue<json>::value);
+        CHECK_FALSE(legacy_ptr_contains<json>::value);
+        CHECK_FALSE(legacy_ptr_subscript<json>::value);
+        CHECK_FALSE(legacy_ptr_subscript_const<json>::value);
+        CHECK_FALSE(legacy_ptr_at<json>::value);
+        CHECK_FALSE(legacy_ptr_at_const<json>::value);
+
+        // the replacement
+        CHECK(ptr_value<json>::value);
+        CHECK(ptr_at<json>::value);
+    }
+
+#endif
+
+    SECTION("the non-deprecated functions still work")
+    {
+        const json j = {{"a", {1, 2}}};
+        const auto cbor = json::to_cbor(j);
+        CHECK(json::from_cbor(cbor.data(), cbor.data() + cbor.size()) == j);
+
+        const json::json_pointer ptr("/a/1");
+        CHECK(ptr == json::json_pointer("/a/1"));
+        CHECK(ptr.to_string() == "/a/1");
+        CHECK(j[ptr] == 2);
+        CHECK(j.at(ptr) == 2);
+        CHECK(j.value(ptr, 0) == 2);
+        CHECK(j.contains(ptr));
+
+        std::ostringstream os;
+        os << j;
+        CHECK(os.str() == R"({"a":[1,2]})");
+        std::istringstream is(os.str());
+        json parsed;
+        is >> parsed;
+        CHECK(parsed == j);
+    }
+}
@@ -16,6 +16,14 @@
    #define JSON_TEST_STRICT_NUL_HANDLING_ENABLED 1
 #endif

+// capture whether JSON_DELETE_DEPRECATED_FUNCTIONS was enabled on the command
+// line *before* including json.hpp, since the library #undefs it once the header
+// has been fully processed (see include/nlohmann/detail/macro_unscope.hpp); the
+// tests of deprecated functions are skipped if these functions are deleted
+#if defined(JSON_DELETE_DEPRECATED_FUNCTIONS) && (JSON_DELETE_DEPRECATED_FUNCTIONS == 1)
+    #define JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
+#endif
+
 #include <nlohmann/json.hpp>
 using nlohmann::json;
 #ifdef JSON_TEST_NO_GLOBAL_UDLS
@@ -291,6 +299,7 @@ TEST_CASE("deserialization")
            }));
        }

+#ifndef JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
        SECTION("operator<<")
        {
            std::stringstream ss;
@@ -299,6 +308,7 @@ TEST_CASE("deserialization")
            j << ss;
            CHECK(j == json({"foo", 1, 2, 3, false, {{"one", 1}}}));
        }
+#endif

        SECTION("operator>>")
        {
@@ -423,6 +433,7 @@ TEST_CASE("deserialization")
            CHECK_THROWS_WITH_AS(_ = json::parse(nullptr), "[json.exception.parse_error.101] parse error: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);
        }

+#ifndef JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
        SECTION("operator<<")
        {
            std::stringstream ss;
@@ -430,6 +441,7 @@ TEST_CASE("deserialization")
            json j;
            CHECK_THROWS_WITH_AS(j << ss, "[json.exception.parse_error.101] parse error at line 1, column 29: syntax error while parsing array - unexpected end of input; expected ']'", json::parse_error&);
        }
+#endif

        SECTION("operator>>")
        {
@@ -1148,9 +1160,9 @@ TEST_CASE("deserialization")
        {
            std::istringstream s(bom + "123 456");
            json j;
-            j << s;
+            s >> j;
            CHECK(j == 123);
-            j << s;
+            s >> j;
            CHECK(j == 456);
        }
    }
@@ -1551,6 +1551,10 @@ TEST_CASE_TEMPLATE("element access 2", Json, nlohmann::json, nlohmann::ordered_j
        // count(0) used to compile and then crash instead of failing to compile
        using nlohmann::detail::is_detected;

+        // MSVC 2015 does not treat selecting a deleted function in decltype as
+        // a substitution failure, so it detects the deleted overloads as
+        // callable; calling them still fails to compile
+#if !(defined(_MSC_VER) && _MSC_VER < 1910)
        CHECK_FALSE(is_detected<can_call_find_with_0, Json&>::value);
        CHECK_FALSE(is_detected<can_call_find_with_0, const Json&>::value);
        CHECK_FALSE(is_detected<can_call_count_with_0, Json&>::value);
@@ -1562,6 +1566,7 @@ TEST_CASE_TEMPLATE("element access 2", Json, nlohmann::json, nlohmann::ordered_j

        // another integral literal type must be rejected as well, not just int
        CHECK_FALSE(is_detected<can_call_contains_with_0L, Json&>::value);
+#endif

        // the valid overloads must remain callable
        CHECK(is_detected<can_call_find, Json&, const char*>::value);
@@ -0,0 +1,246 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#include "doctest_compatibility.h"
+
+// skip tests if JSON_DisableEnumSerialization=ON (#4384)
+#if defined(JSON_DISABLE_ENUM_SERIALIZATION) && (JSON_DISABLE_ENUM_SERIALIZATION == 1)
+    #define SKIP_TESTS_FOR_ENUM_SERIALIZATION
+#endif
+
+// This file tests the opt-in JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS, so it defines
+// the macro itself rather than relying on a -D flag, and runs in every build.
+// The default behavior is tested in unit-enum_keyed_maps_default.cpp.
+#ifdef JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
+    #undef JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
+#endif
+
+#define JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS 1
+
+#include <nlohmann/json.hpp>
+using nlohmann::json;
+using nlohmann::ordered_json;
+
+#include <cstddef>
+#include <functional>
+#include <map>
+#include <string>
+#include <unordered_map>
+#include <utility>
+#include <vector>
+
+#define STRINGIZE_EX(x) #x
+#define STRINGIZE(x) STRINGIZE_EX(x)
+
+// NLOHMANN_JSON_SERIALIZE_ENUM uses a static std::pair
+DOCTEST_CLANG_SUPPRESS_WARNING_PUSH
+DOCTEST_CLANG_SUPPRESS_WARNING("-Wexit-time-destructors")
+
+namespace
+{
+// std::hash is only required for enums since C++14
+struct enum_hash
+{
+    template<typename T>
+    std::size_t operator()(T t) const noexcept
+    {
+        return static_cast<std::size_t>(t);
+    }
+};
+} // namespace
+
+// the example from #4378
+enum TaskState // NOLINT(cert-int09-c,readability-enum-initial-value,cppcoreguidelines-use-enum-class)
+{
+    TS_STOPPED,
+    TS_RUNNING,
+    TS_COMPLETED,
+    TS_INVALID = -1,
+};
+
+// NOLINTNEXTLINE(misc-const-correctness,misc-use-internal-linkage,cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays) - false positive
+NLOHMANN_JSON_SERIALIZE_ENUM(TaskState,
+{
+    {TS_INVALID, nullptr},
+    {TS_STOPPED, "stopped"},
+    {TS_RUNNING, "running"},
+    {TS_COMPLETED, "completed"},
+})
+
+enum class color {red, green, blue}; // blue is not mapped and falls back to "red"
+
+// NOLINTNEXTLINE(misc-const-correctness,misc-use-internal-linkage,cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays) - false positive
+NLOHMANN_JSON_SERIALIZE_ENUM(color,
+{
+    {color::red, "red"},
+    {color::green, "green"},
+})
+
+enum class strict_color {red, green, blue}; // blue is not mapped
+
+// NOLINTNEXTLINE(misc-const-correctness,misc-use-internal-linkage,cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays) - false positive
+NLOHMANN_JSON_SERIALIZE_ENUM_STRICT(strict_color,
+{
+    {strict_color::red, "red"},
+    {strict_color::green, "green"},
+})
+
+enum class digit {zero, one};
+
+// NOLINTNEXTLINE(misc-const-correctness,misc-use-internal-linkage,cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays) - false positive
+NLOHMANN_JSON_SERIALIZE_ENUM(digit,
+{
+    {digit::zero, 0},
+    {digit::one, 1},
+})
+
+#ifndef SKIP_TESTS_FOR_ENUM_SERIALIZATION
+enum class plain {zero, one}; // serialized as integer
+#endif
+
+TEST_CASE("JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS")
+{
+    SECTION("the macro is part of the ABI tag")
+    {
+        const std::string ns = STRINGIZE(NLOHMANN_JSON_NAMESPACE);
+        CHECK(ns.find("_ekmo") != std::string::npos);
+    }
+
+    SECTION("std::map (#4378)")
+    {
+        using task_map = std::map<TaskState, std::string>;
+        const task_map m = {{TS_STOPPED, "aa"}, {TS_COMPLETED, "bb"}};
+        const json j = m;
+        CHECK(j == json::parse(R"({"stopped":"aa","completed":"bb"})"));
+        CHECK(j.get<task_map>() == m);
+
+        json j2;
+        j2["x"] = m;
+        CHECK(j2.dump() == R"({"x":{"completed":"bb","stopped":"aa"}})");
+    }
+
+    SECTION("std::map with custom comparator")
+    {
+        using task_map = std::map<TaskState, int, std::greater<TaskState>>;
+        const task_map m = {{TS_STOPPED, 1}, {TS_RUNNING, 2}};
+        const json j = m;
+        CHECK(j == json::parse(R"({"stopped":1,"running":2})"));
+        CHECK(j.get<task_map>() == m);
+    }
+
+    SECTION("std::unordered_map")
+    {
+        using task_map = std::unordered_map<TaskState, int, enum_hash>;
+        const task_map m = {{TS_STOPPED, 1}, {TS_RUNNING, 2}};
+        const json j = m;
+        CHECK(j == json::parse(R"({"stopped":1,"running":2})"));
+        CHECK(j.get<task_map>() == m);
+    }
+
+    SECTION("nested maps")
+    {
+        using nested_map = std::map<color, std::map<TaskState, int>>;
+        const nested_map m = {{color::green, {{TS_RUNNING, 1}}}, {color::red, {}}};
+        const json j = m;
+        CHECK(j == json::parse(R"({"green":{"running":1},"red":{}})"));
+        CHECK(j.get<nested_map>() == m);
+    }
+
+    SECTION("ordered_json keeps the order of the map")
+    {
+        using task_map = std::map<TaskState, int>;
+        const task_map m = {{TS_STOPPED, 1}, {TS_RUNNING, 2}, {TS_COMPLETED, 3}};
+        const ordered_json j = m;
+        CHECK(j.dump() == R"({"stopped":1,"running":2,"completed":3})");
+        CHECK(j.get<task_map>() == m);
+    }
+
+    SECTION("empty map")
+    {
+        const json j = std::map<TaskState, int>();
+        CHECK(j.is_object());
+        CHECK(j.empty());
+    }
+
+    SECTION("NLOHMANN_JSON_SERIALIZE_ENUM_STRICT")
+    {
+        using color_map = std::map<strict_color, int>;
+        const color_map m = {{strict_color::red, 1}, {strict_color::green, 2}};
+        const json j = m;
+        CHECK(j == json::parse(R"({"red":1,"green":2})"));
+        CHECK(j.get<color_map>() == m);
+
+        const color_map unmapped = {{strict_color::blue, 1}};
+        json _;
+        CHECK_THROWS_WITH_AS(_ = unmapped,
+                             "[json.exception.out_of_range.410] enum value out of range for strict_color", json::out_of_range&);
+    }
+
+    SECTION("arrays of [key, value] pairs are still read")
+    {
+        using task_map = std::map<TaskState, int>;
+        const task_map m = {{TS_STOPPED, 1}};
+        CHECK(json::parse(R"([["stopped",1]])").get<task_map>() == m);
+    }
+
+    SECTION("other containers are not affected")
+    {
+        const std::vector<std::pair<TaskState, int>> pairs = {{TS_STOPPED, 1}};
+        const std::map<std::string, TaskState> string_keys = {{"a", TS_STOPPED}};
+        const std::map<int, int> int_keys = {{1, 2}};
+        CHECK(json(pairs) == json::parse(R"([["stopped",1]])"));
+        CHECK(json(string_keys) == json::parse(R"({"a":"stopped"})"));
+        CHECK(json(int_keys) == json::parse("[[1,2]]"));
+    }
+
+    SECTION("maps with non-unique keys are still stored as arrays of pairs")
+    {
+        const std::multimap<TaskState, int> mm = {{TS_STOPPED, 1}, {TS_STOPPED, 2}};
+        const std::unordered_multimap<TaskState, int, enum_hash> umm = {{TS_RUNNING, 3}, {TS_RUNNING, 3}};
+        CHECK(json(mm) == json::parse(R"([["stopped",1],["stopped",2]])"));
+        CHECK(json(umm) == json::parse(R"([["running",3],["running",3]])"));
+    }
+
+    SECTION("keys that do not serialize to strings")
+    {
+        const std::map<TaskState, int> null_key = {{TS_INVALID, 1}};
+        const std::map<digit, int> number_key = {{digit::zero, 1}};
+        json j = "unchanged";
+
+        // mapped to null
+        CHECK_THROWS_WITH_AS(j = null_key,
+                             "[json.exception.type_error.302] type must be string, but is null", json::type_error&);
+
+        // mapped to a number
+        CHECK_THROWS_WITH_AS(j = number_key,
+                             "[json.exception.type_error.302] type must be string, but is number", json::type_error&);
+
+#ifndef SKIP_TESTS_FOR_ENUM_SERIALIZATION
+        // enum without NLOHMANN_JSON_SERIALIZE_ENUM
+        const std::map<plain, int> plain_key = {{plain::zero, 1}};
+        CHECK_THROWS_WITH_AS(j = plain_key,
+                             "[json.exception.type_error.302] type must be string, but is number", json::type_error&);
+#endif
+
+        CHECK(j == "unchanged");
+    }
+
+    SECTION("keys that serialize to the same string")
+    {
+        const std::map<color, int> m = {{color::red, 1}, {color::blue, 2}};
+        json j = "unchanged";
+
+        // color::blue is not mapped and falls back to "red"
+        CHECK_THROWS_WITH_AS(j = m,
+                             "[json.exception.type_error.318] duplicate object key 'red'", json::type_error&);
+
+        CHECK(j == "unchanged");
+    }
+}
+
+DOCTEST_CLANG_SUPPRESS_WARNING_POP
@@ -0,0 +1,144 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#include "doctest_compatibility.h"
+
+// This file tests maps with enum keys with the default setting of
+// JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS (or whatever a -D flag sets it to).
+// unit-enum_keyed_maps.cpp tests JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS=1.
+// These tests are not part of unit-conversions.cpp, because that object file
+// is already too big for the MinGW linker of some compilers.
+
+#include <nlohmann/json.hpp>
+using nlohmann::json;
+
+#include <cstddef>
+#include <functional>
+#include <map>
+#include <string>
+#include <unordered_map>
+
+// NLOHMANN_JSON_SERIALIZE_ENUM uses a static std::pair
+DOCTEST_CLANG_SUPPRESS_WARNING_PUSH
+DOCTEST_CLANG_SUPPRESS_WARNING("-Wexit-time-destructors")
+
+enum class cards {kreuz, pik, herz, karo};
+
+// NOLINTNEXTLINE(misc-use-internal-linkage,misc-const-correctness,cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays) - false positive
+NLOHMANN_JSON_SERIALIZE_ENUM(cards,
+{
+    {cards::kreuz, "kreuz"},
+    {cards::pik, "pik"},
+    {cards::herz, "herz"},
+    {cards::karo, "karo"}
+})
+
+enum TaskState // NOLINT(cert-int09-c,readability-enum-initial-value,cppcoreguidelines-use-enum-class)
+{
+    TS_STOPPED,
+    TS_RUNNING,
+    TS_COMPLETED,
+    TS_INVALID = -1,
+};
+
+// NOLINTNEXTLINE(misc-const-correctness,misc-use-internal-linkage,cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays) - false positive
+NLOHMANN_JSON_SERIALIZE_ENUM(TaskState,
+{
+    {TS_INVALID, nullptr},
+    {TS_STOPPED, "stopped"},
+    {TS_RUNNING, "running"},
+    {TS_COMPLETED, "completed"},
+})
+
+enum class strict_cards {kreuz, pik, herz, karo, andere}; // andere not included in mapping
+
+// NOLINTNEXTLINE(misc-use-internal-linkage,misc-const-correctness,cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays) - false positive
+NLOHMANN_JSON_SERIALIZE_ENUM_STRICT(strict_cards,
+{
+    {strict_cards::kreuz, "kreuz"},
+    {strict_cards::pik, "pik"},
+    {strict_cards::herz, "herz"},
+    {strict_cards::karo, "karo"}
+})
+
+namespace
+{
+// std::hash is only required for enums since C++14
+struct enum_hash
+{
+    template<typename T>
+    std::size_t operator()(T t) const noexcept
+    {
+        return static_cast<std::size_t>(t);
+    }
+};
+} // namespace
+
+// see unit-enum_keyed_maps.cpp for JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS=1
+TEST_CASE("maps with enum keys")
+{
+    using task_map = std::map<TaskState, std::string>;
+    using task_umap = std::unordered_map<TaskState, std::string, enum_hash>;
+    using task_gmap = std::map<TaskState, std::string, std::greater<TaskState>>;
+    using nested_map = std::map<cards, std::map<TaskState, int>>;
+    using strict_map = std::map<strict_cards, int>;
+    using int_map = std::map<int, int>;
+    using int_umap = std::unordered_map<int, int>;
+
+    const task_map m = {{TS_STOPPED, "aa"}, {TS_COMPLETED, "bb"}};
+
+#if !JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
+    SECTION("stored as array of pairs")
+    {
+        CHECK(json(m) == json::parse(R"([["stopped","aa"],["completed","bb"]])"));
+        CHECK(json(task_umap {{TS_RUNNING, "cc"}}) == json::parse(R"([["running","cc"]])"));
+    }
+#endif
+
+    SECTION("read from array of pairs")
+    {
+        CHECK(json::parse(R"([["stopped","aa"],["completed","bb"]])").get<task_map>() == m);
+    }
+
+    SECTION("read from object (#4378)")
+    {
+        const json j = json::parse(R"({"stopped":"aa","completed":"bb"})");
+        CHECK(j.get<task_map>() == m);
+        CHECK(j.get<task_umap>() == task_umap(m.begin(), m.end()));
+        CHECK(j.get<task_gmap>() == task_gmap(m.begin(), m.end()));
+        CHECK(json::parse(R"({"kreuz":{"stopped":1}})").get<nested_map>() == nested_map {{cards::kreuz, {{TS_STOPPED, 1}}}});
+        CHECK(nlohmann::ordered_json::parse(R"({"stopped":"aa","completed":"bb"})").get<task_map>() == m);
+
+        // object keys go through the enum's from_json
+        strict_map sm;
+        CHECK_THROWS_WITH_AS(json::parse(R"({"what?":1})").get_to(sm),
+                             "[json.exception.out_of_range.410] enum value out of range for strict_cards: \"what?\"", json::out_of_range&);
+    }
+
+    SECTION("objects are only read for enum keys")
+    {
+        // built rather than parsed, so that the messages do not gain a byte
+        // range with JSON_DIAGNOSTIC_POSITIONS
+        const json j = {{"1", 2}};
+        int_map im;
+        int_umap ium;
+        CHECK_THROWS_WITH_AS(j.get_to(im),
+                             "[json.exception.type_error.302] type must be array, but is object", json::type_error&);
+        CHECK_THROWS_WITH_AS(j.get_to(ium),
+                             "[json.exception.type_error.302] type must be array, but is object", json::type_error&);
+    }
+
+    SECTION("other types are rejected")
+    {
+        task_map tm;
+        CHECK_THROWS_WITH_AS(json("stopped").get_to(tm),
+                             "[json.exception.type_error.302] type must be array, but is string", json::type_error&);
+    }
+}
+
+DOCTEST_CLANG_SUPPRESS_WARNING_POP
@@ -8,6 +8,14 @@

 #include "doctest_compatibility.h"

+// capture whether JSON_DELETE_DEPRECATED_FUNCTIONS was enabled on the command
+// line *before* including json.hpp, since the library #undefs it once the header
+// has been fully processed (see include/nlohmann/detail/macro_unscope.hpp); the
+// tests of deprecated functions are skipped if these functions are deleted
+#if defined(JSON_DELETE_DEPRECATED_FUNCTIONS) && (JSON_DELETE_DEPRECATED_FUNCTIONS == 1)
+    #define JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
+#endif
+
 #include <nlohmann/json.hpp>
 using nlohmann::json;

@@ -19,6 +27,7 @@ DOCTEST_GCC_SUPPRESS_WARNING_PUSH
 DOCTEST_CLANG_SUPPRESS_WARNING_PUSH
 DOCTEST_CLANG_SUPPRESS_WARNING("-Wrange-loop-construct")

+#ifndef JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
 TEST_CASE("iterator_wrapper")
 {
    SECTION("object")
@@ -715,6 +724,7 @@ TEST_CASE("iterator_wrapper")
        }
    }
 }
+#endif

 TEST_CASE("items()")
 {
@@ -9,6 +9,14 @@
 #include "doctest_compatibility.h"

 #define JSON_TESTS_PRIVATE
+// capture whether JSON_DELETE_DEPRECATED_FUNCTIONS was enabled on the command
+// line *before* including json.hpp, since the library #undefs it once the header
+// has been fully processed (see include/nlohmann/detail/macro_unscope.hpp); the
+// tests of deprecated functions are skipped if these functions are deleted
+#if defined(JSON_DELETE_DEPRECATED_FUNCTIONS) && (JSON_DELETE_DEPRECATED_FUNCTIONS == 1)
+    #define JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
+#endif
+
 #include <nlohmann/json.hpp>
 using nlohmann::json;
 #ifdef JSON_TEST_NO_GLOBAL_UDLS
@@ -564,7 +572,9 @@ TEST_CASE("JSON pointers")
            std::stringstream ss;
            ss << ptr;
            CHECK(ptr.to_string() == ptr_str);
+#ifndef JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
            CHECK(std::string(ptr) == ptr_str);
+#endif
            CHECK(ss.str() == ptr_str);
        }
    }
@@ -744,8 +754,6 @@ TEST_CASE("JSON pointers")

    SECTION("equality comparison")
    {
-        const char* ptr_cpstring = "/foo/bar";
-        const char ptr_castring[] = "/foo/bar"; // NOLINT(misc-const-correctness,hicpp-avoid-c-arrays,modernize-avoid-c-arrays,cppcoreguidelines-avoid-c-arrays)
        std::string ptr_string{"/foo/bar"};
        auto ptr1 = json::json_pointer(ptr_string);
        auto ptr2 = json::json_pointer(ptr_string);
@@ -755,6 +763,12 @@ TEST_CASE("JSON pointers")

        CHECK(ptr1 == ptr2);

+        CHECK_FALSE(ptr1 != ptr2);
+
+#ifndef JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
+        const char* ptr_cpstring = "/foo/bar";
+        const char ptr_castring[] = "/foo/bar"; // NOLINT(misc-const-correctness,hicpp-avoid-c-arrays,modernize-avoid-c-arrays,cppcoreguidelines-avoid-c-arrays)
+
        CHECK(ptr1 == "/foo/bar");
        CHECK(ptr1 == ptr_cpstring);
        CHECK(ptr1 == ptr_castring);
@@ -765,8 +779,6 @@ TEST_CASE("JSON pointers")
        CHECK(ptr_castring == ptr1);
        CHECK(ptr_string == ptr1);

-        CHECK_FALSE(ptr1 != ptr2);
-
        CHECK_FALSE(ptr1 != "/foo/bar");
        CHECK_FALSE(ptr1 != ptr_cpstring);
        CHECK_FALSE(ptr1 != ptr_castring);
@@ -788,6 +800,7 @@ TEST_CASE("JSON pointers")
            CHECK_THROWS_WITH_AS("/~~" == ptr1,
                                 "[json.exception.parse_error.108] parse error: escape character '~' must be followed with '0' or '1'", json::parse_error&);
        }
+#endif
    }

    SECTION("less-than comparison")
@@ -839,6 +852,7 @@ TEST_CASE("JSON pointers")
        json_ptr_j ptr_j{ptr_string};
        json_ptr_oj ptr_oj{ptr_string};

+#ifndef JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
        CHECK(j.contains(ptr));
        CHECK(j.contains(ptr_j));
        CHECK(j.contains(ptr_oj));
@@ -851,6 +865,7 @@ TEST_CASE("JSON pointers")

        CHECK(j.value(ptr, "x") == j.value(ptr_j, "x"));
        CHECK(j.value(ptr, "x") == j.value(ptr_oj, "x"));
+#endif

        CHECK(ptr == ptr_j);
        CHECK(ptr == ptr_oj);
@@ -260,10 +260,11 @@ struct LocaleSwitchingSax final: public nlohmann::json_sax<json>

 TEST_CASE("locale changes between lexer construction and number conversion (#5198)")
 {
-    // The numbers are chosen so that the conversion also takes the strtod
-    // fallback, which honors the locale that is current at conversion time:
-    // too many significant digits for Clinger's fast path, an underflow that
-    // std::from_chars rejects, and a plain value.
+    // float and double are converted without the locale. A long double that
+    // is not binary64 can take the strtold fallback, which honors the locale
+    // that is current at conversion time. The numbers are chosen so that it
+    // does: too many significant digits for Clinger's fast path, an underflow
+    // that std::from_chars rejects, and a plain value.
    const std::vector<std::string> numbers = {"3.14159265358979323846", "1.5e-400", "12.34", "-0.000123456789012345678"};
    std::string text = "[";
    for (const auto& n : numbers)
@@ -327,7 +328,8 @@ TEST_CASE("locale changes between lexer construction and number conversion (#519
            }
        }

-        // a long double goes through std::strtold unless std::from_chars supports it
+        // a long double goes through std::strtold unless it is binary64 or
+        // std::from_chars supports it
        {
            bool switched = false;
            const auto cb = [&](int /*depth*/, long_double_json::parse_event_t event, long_double_json& /*parsed*/) noexcept
@@ -353,8 +355,15 @@ TEST_CASE("locale with a multi-byte decimal point")
 {
    // Some locales use a decimal point that is not a single character, e.g.
    // U+066B ARABIC DECIMAL SEPARATOR (two bytes in UTF-8). It cannot be
-    // substituted in place for '.', so the strtod fallback stops early. The
-    // conversion must still terminate rather than retry forever.
+    // substituted in place for '.', so the strtold fallback (only for long
+    // double formats other than binary64) converts a copy of the token with
+    // the whole decimal point instead (#5660). The values must be those of the
+    // "C" locale.
+    using long_double_json = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t, long double>;
+    const char* const long_double_numbers = "[3.14159265358979323846, 1.5e-400, -0.000123456789012345678]";
+    REQUIRE(std::setlocale(LC_NUMERIC, "C") != nullptr);
+    const long_double_json expected_long_double = long_double_json::parse(long_double_numbers);
+
    const std::array<const char*, 6> names = {{"ar_EG.UTF-8", "ar_SA.UTF-8", "fa_IR.UTF-8", "ps_AF.UTF-8", "ar_EG", "fa_IR"}};
    bool tested = false;
    for (const char* name : names)
@@ -372,12 +381,20 @@ TEST_CASE("locale with a multi-byte decimal point")
        tested = true;

        // too many significant digits for Clinger's fast path, and an underflow
-        // that std::from_chars rejects: both reach the strtod fallback
+        // that std::from_chars rejects: double does not depend on the locale
        json j;
        CHECK_NOTHROW(j = json::parse("[3.14159265358979323846, 1.5e-400, -0.000123456789012345678]"));
        CHECK(j.is_array());
+        CHECK(j[0] == 3.14159265358979323846);
+        CHECK(j[1] == 0.0);
+        CHECK(j[2] == -0.000123456789012345678);
        CHECK(json::accept("3.14159265358979323846"));

+        // a long double that reaches the strtold fallback is not truncated
+        long_double_json ld;
+        CHECK_NOTHROW(ld = long_double_json::parse(long_double_numbers));
+        CHECK(ld == expected_long_double);
+
        // a value the locale-independent paths convert is not affected
        CHECK(json::parse("12.5") == 12.5);
    }
@@ -8,6 +8,14 @@

 #include "doctest_compatibility.h"

+// capture whether JSON_DELETE_DEPRECATED_FUNCTIONS was enabled on the command
+// line *before* including json.hpp, since the library #undefs it once the header
+// has been fully processed (see include/nlohmann/detail/macro_unscope.hpp); the
+// tests of deprecated functions are skipped if these functions are deleted
+#if defined(JSON_DELETE_DEPRECATED_FUNCTIONS) && (JSON_DELETE_DEPRECATED_FUNCTIONS == 1)
+    #define JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
+#endif
+
 #include <nlohmann/json.hpp>
 using nlohmann::json;
 #ifdef JSON_TEST_NO_GLOBAL_UDLS
@@ -33,10 +41,49 @@ TEST_CASE("MessagePack")
    {
        SECTION("discarded")
        {
-            // discarded values are not serialized
+            // a discarded value cannot be serialized to MessagePack
            json const j = json::value_t::discarded;
-            const auto result = json::to_msgpack(j);
-            CHECK(result.empty());
+            CHECK_THROWS_WITH_AS(json::to_msgpack(j), "[json.exception.type_error.321] cannot serialize discarded value to MessagePack", json::type_error&);
+        }
+
+        SECTION("discarded values nested in a container")
+        {
+            json const discarded = json::value_t::discarded;
+
+            SECTION("in an array")
+            {
+                json const j = {1, discarded, 2};
+#if JSON_DIAGNOSTICS
+                CHECK_THROWS_WITH_AS(json::to_msgpack(j), "[json.exception.type_error.321] (/1) cannot serialize discarded value to MessagePack", json::type_error&);
+#else
+                CHECK_THROWS_WITH_AS(json::to_msgpack(j), "[json.exception.type_error.321] cannot serialize discarded value to MessagePack", json::type_error&);
+#endif
+            }
+
+            SECTION("as an object value")
+            {
+                json j;
+                j["a"] = 1;
+                j["b"] = discarded;
+#if JSON_DIAGNOSTICS
+                CHECK_THROWS_WITH_AS(json::to_msgpack(j), "[json.exception.type_error.321] (/b) cannot serialize discarded value to MessagePack", json::type_error&);
+#else
+                CHECK_THROWS_WITH_AS(json::to_msgpack(j), "[json.exception.type_error.321] cannot serialize discarded value to MessagePack", json::type_error&);
+#endif
+            }
+
+            SECTION("nested deeper (array in object in array)")
+            {
+                json inner_array = {1, discarded};
+                json middle_object;
+                middle_object["x"] = inner_array;
+                json const j = {middle_object};
+#if JSON_DIAGNOSTICS
+                CHECK_THROWS_WITH_AS(json::to_msgpack(j), "[json.exception.type_error.321] (/0/x/1) cannot serialize discarded value to MessagePack", json::type_error&);
+#else
+                CHECK_THROWS_WITH_AS(json::to_msgpack(j), "[json.exception.type_error.321] cannot serialize discarded value to MessagePack", json::type_error&);
+#endif
+            }
        }

        SECTION("null")
@@ -1795,8 +1842,10 @@ TEST_CASE("MessagePack input that cannot be read is discarded by every overload"
    CHECK_THROWS_AS(_ = json::from_msgpack(input.begin(), input.end()), json::parse_error&);
    CHECK(json::from_msgpack(input, true, false).is_discarded());
    CHECK(json::from_msgpack(input.begin(), input.end(), true, false).is_discarded());
+#ifndef JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
    CHECK(json::from_msgpack(input.data(), input.size(), true, false).is_discarded());
    CHECK(json::from_msgpack({input.data(), input.size()}, true, false).is_discarded());
+#endif
 }

 TEST_CASE("MessagePack SAX parsing stops at every event")
@@ -2099,12 +2148,14 @@ TEST_CASE("MessagePack roundtrips" * doctest::skip())
                CHECK(j1 == j2);
            }

+#ifndef JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
            {
                INFO_WITH_TEMP(filename + ": uint8_t* and size");
                json j2;
                CHECK_NOTHROW(j2 = json::from_msgpack({packed.data(), packed.size()}));
                CHECK(j1 == j2);
            }
+#endif

            {
                INFO_WITH_TEMP(filename + ": output to output adapters");
@@ -40,7 +40,9 @@ using ordered_json = nlohmann::ordered_json;
 #endif

 #include <cstdio>
+#include <cstdlib>
 #include <list>
+#include <new>
 #include <tuple>
 #include <type_traits>
 #include <utility>
@@ -107,6 +109,84 @@ DOCTEST_CLANG_SUPPRESS_WARNING("-Wexit-time-destructors")

 using float_json = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t, float>;

+#if (defined(__cpp_exceptions) || defined(__EXCEPTIONS) || defined(_CPPUNWIND)) && !defined(JSON_NOEXCEPTION)
+namespace
+{
+// An allocator whose allocate() can be told to fail on demand, so tests can
+// check that ~basic_json() tolerates - in fact, after #5135, never even
+// triggers - an allocation failure. This replaces an earlier version of
+// this test that overrode the process-wide ::operator new/::operator
+// delete, which affected every allocation in the whole unit-regression2
+// binary rather than just the values under test.
+std::size_t failing_allocator_allocations = 0;
+std::size_t failing_allocator_deallocations = 0;
+bool fail_next_allocation = false;
+
+template<class T>
+struct failing_allocator : std::allocator<T>
+{
+    using std::allocator<T>::allocator;
+
+    failing_allocator() noexcept = default;
+    template<class U>
+    failing_allocator(const failing_allocator<U>& /*unused*/) noexcept {} // NOLINT(google-explicit-constructor)
+
+    T* allocate(std::size_t n)
+    {
+        if (fail_next_allocation)
+        {
+            fail_next_allocation = false;
+            throw std::bad_alloc();
+        }
+        ++failing_allocator_allocations;
+        return std::allocator<T>::allocate(n);
+    }
+
+    void deallocate(T* p, std::size_t n)
+    {
+        ++failing_allocator_deallocations;
+        std::allocator<T>::deallocate(p, n);
+    }
+
+    template<class U>
+    struct rebind
+    {
+        using other = failing_allocator<U>;
+    };
+};
+
+using failing_json = nlohmann::basic_json<std::map, std::vector, std::string, bool,
+      std::int64_t, std::uint64_t, double, failing_allocator>;
+using failing_ordered_json = nlohmann::basic_json<nlohmann::ordered_map, std::vector, std::string, bool,
+      std::int64_t, std::uint64_t, double, failing_allocator>;
+
+// builds `depth` levels of nesting around a scalar, iteratively (never
+// recursing: each wrap only moves the previous, already-built value, which
+// is O(1)), each level an array or an object depending on `nest_objects`
+template<class BasicJsonType>
+BasicJsonType make_deep_nest(std::size_t depth, bool nest_objects)
+{
+    BasicJsonType v = 0;
+    for (std::size_t i = 0; i < depth; ++i)
+    {
+        if (nest_objects)
+        {
+            BasicJsonType wrapper = BasicJsonType::object();
+            wrapper["x"] = std::move(v);
+            v = std::move(wrapper);
+        }
+        else
+        {
+            BasicJsonType wrapper = BasicJsonType::array();
+            wrapper.push_back(std::move(v));
+            v = std::move(wrapper);
+        }
+    }
+    return v;
+}
+} // namespace
+#endif
+
 /////////////////////////////////////////////////////////////////////
 // for #1647
 /////////////////////////////////////////////////////////////////////
@@ -569,7 +649,7 @@ TEST_CASE("regression tests 2")
    SECTION("issue #2067 - cannot serialize binary data to text JSON")
    {
        const std::array<unsigned char, 23> data = {{0x81, 0xA4, 0x64, 0x61, 0x74, 0x61, 0xC4, 0x0F, 0x33, 0x30, 0x30, 0x32, 0x33, 0x34, 0x30, 0x31, 0x30, 0x37, 0x30, 0x35, 0x30, 0x31, 0x30}};
-        const json j = json::from_msgpack(data.data(), data.size());
+        const json j = json::from_msgpack(data.begin(), data.end());
        // dump() is nodiscard; this only checks that dumping does not throw
        CHECK_NOTHROW(
            utils::ignore_return_value(
@@ -940,4 +1020,211 @@ TEST_CASE("regression test - excessive binary container size honors allow_except
    CHECK(json::from_cbor(std::vector<std::uint8_t> {0x9b, 0, 0, 0, 0, 0, 0, 0, 0x02}, true, false).is_discarded());
 }

+#if (defined(__cpp_exceptions) || defined(__EXCEPTIONS) || defined(_CPPUNWIND)) && !defined(JSON_NOEXCEPTION)
+TEST_CASE("regression test #5135 - destructor never allocates, even under memory pressure")
+{
+    // Before the fix, ~basic_json() flattened a nested array/object into a
+    // heap-allocated std::vector to avoid recursing; that allocation could
+    // itself throw bad_alloc, which escapes a noexcept destructor and
+    // terminates the program. destroy() no longer allocates anything, so
+    // none of the sections below ever observe fail_next_allocation being
+    // consumed: CHECK(fail_next_allocation) confirms it was never touched.
+
+    SECTION("the original report: a small, mixed array/object nest")
+    {
+        failing_allocator_allocations = 0;
+        failing_allocator_deallocations = 0;
+        {
+            failing_json j = failing_json::array(
+            {
+                failing_json::array({1, 2}),
+                failing_json::object({{"key", failing_json::array({3})}})
+            });
+            fail_next_allocation = true;
+        } // j is destroyed here, with every further allocation set to fail
+
+        CHECK(fail_next_allocation);
+        fail_next_allocation = false;
+        CHECK(failing_allocator_deallocations > 0);
+    }
+
+    SECTION("100000-deep nested array")
+    {
+        std::size_t allocations_before = 0;
+        {
+            failing_json j = make_deep_nest<failing_json>(100000, false);
+            allocations_before = failing_allocator_allocations;
+            fail_next_allocation = true;
+        }
+
+        CHECK(fail_next_allocation);
+        fail_next_allocation = false;
+        CHECK(failing_allocator_allocations == allocations_before);
+    }
+
+    SECTION("100000-deep nested object")
+    {
+        std::size_t allocations_before = 0;
+        {
+            failing_json j = make_deep_nest<failing_json>(100000, true);
+            allocations_before = failing_allocator_allocations;
+            fail_next_allocation = true;
+        }
+
+        CHECK(fail_next_allocation);
+        fail_next_allocation = false;
+        CHECK(failing_allocator_allocations == allocations_before);
+    }
+
+    SECTION("100000-deep nested ordered_json")
+    {
+        std::size_t allocations_before = 0;
+        {
+            failing_ordered_json j = make_deep_nest<failing_ordered_json>(100000, true);
+            allocations_before = failing_allocator_allocations;
+            fail_next_allocation = true;
+        }
+
+        CHECK(fail_next_allocation);
+        fail_next_allocation = false;
+        CHECK(failing_allocator_allocations == allocations_before);
+    }
+
+    SECTION("wide and deep: 1000 arrays of 1000 elements, each a small nested object")
+    {
+        std::size_t allocations_before = 0;
+        {
+            failing_json wide = failing_json::array();
+            for (std::size_t i = 0; i < 1000; ++i)
+            {
+                failing_json inner = failing_json::array();
+                for (std::size_t k = 0; k < 1000; ++k)
+                {
+                    inner.push_back(failing_json::object({{"a", 1}, {"b", failing_json::array({1, 2, 3})}}));
+                }
+                wide.push_back(std::move(inner));
+            }
+
+            allocations_before = failing_allocator_allocations;
+            fail_next_allocation = true;
+        }
+
+        CHECK(fail_next_allocation);
+        fail_next_allocation = false;
+        CHECK(failing_allocator_allocations == allocations_before);
+    }
+}
+#endif
+
+namespace
+{
+// a single-element chain of `depth` arrays, built iteratively (never
+// recursing: each wrap only moves the previous, already-built value)
+template<class BasicJsonType>
+BasicJsonType make_single_chain(std::size_t depth)
+{
+    BasicJsonType v = 1;
+    for (std::size_t i = 0; i < depth; ++i)
+    {
+        BasicJsonType wrapper = BasicJsonType::array();
+        wrapper.push_back(std::move(v));
+        v = std::move(wrapper);
+    }
+    return v;
+}
+
+// copies value first, to make sure nothing was corrupted by building it,
+// then lets both the copy and the original destruct via normal scope exit
+template<class BasicJsonType>
+void check_destroy_edge_case(const BasicJsonType& value)
+{
+    const BasicJsonType copy = value;
+    CHECK(copy == value);
+}
+} // namespace
+
+TEST_CASE_TEMPLATE("regression test #5135 - destroy() edge cases", BasicJsonType, json, ordered_json)
+{
+    using binary_t = typename BasicJsonType::binary_t;
+
+    SECTION("mix of empty objects, empty arrays, non-empty containers, and scalars")
+    {
+        BasicJsonType root = BasicJsonType::array();
+        root.push_back(BasicJsonType::object());
+        root.push_back(BasicJsonType::array());
+        root.push_back(BasicJsonType::object({{"k", 1}}));
+        root.push_back(BasicJsonType::array({1, 2, 3}));
+        root.push_back(nullptr);
+        root.push_back(true);
+        root.push_back(42);
+        root.push_back(3.14);
+        root.push_back("a string");
+        root.push_back(BasicJsonType(binary_t({1, 2, 3})));
+        check_destroy_edge_case(root);
+    }
+
+    SECTION("container child in first position only")
+    {
+        BasicJsonType root = BasicJsonType::array({BasicJsonType::array({1, 2}), 3, 4, 5});
+        check_destroy_edge_case(root);
+    }
+
+    SECTION("container child in last position only")
+    {
+        BasicJsonType root = BasicJsonType::array({1, 2, 3, BasicJsonType::array({4, 5})});
+        check_destroy_edge_case(root);
+    }
+
+    SECTION("container children in first and last position")
+    {
+        BasicJsonType root = BasicJsonType::array({BasicJsonType::array({1}), 2, 3, BasicJsonType::array({4})});
+        check_destroy_edge_case(root);
+    }
+
+    SECTION("single-element chain, 1000 levels deep")
+    {
+        BasicJsonType root = make_single_chain<BasicJsonType>(1000);
+        check_destroy_edge_case(root);
+    }
+
+    SECTION("top-level empty array")
+    {
+        BasicJsonType root = BasicJsonType::array();
+        check_destroy_edge_case(root);
+    }
+
+    SECTION("top-level empty object")
+    {
+        BasicJsonType root = BasicJsonType::object();
+        check_destroy_edge_case(root);
+    }
+
+    SECTION("object whose last child is a non-empty array whose last child is an empty object")
+    {
+        BasicJsonType inner_array = BasicJsonType::array({1, 2, BasicJsonType::object()});
+        BasicJsonType root = BasicJsonType::object({{"a", 1}, {"b", inner_array}});
+        check_destroy_edge_case(root);
+    }
+
+    SECTION("destruction via erase() on a deeply nested child")
+    {
+        BasicJsonType root = BasicJsonType::array();
+        root.push_back(make_single_chain<BasicJsonType>(500));
+        root.push_back(BasicJsonType::object({{"k", BasicJsonType::array({1, 2, 3})}}));
+        // erase() must destroy the removed subtree without recursing or
+        // allocating beyond what erase() itself needs
+        root.erase(0);
+        CAPTURE(root.size())
+        CHECK(root.size() == 1);
+    }
+
+    SECTION("destruction via assignment on a deep tree")
+    {
+        BasicJsonType root = make_single_chain<BasicJsonType>(2000);
+        // assigning a new value destroys the old one in place
+        root = nullptr;
+        CHECK(root.is_null());
+    }
+}
+
 DOCTEST_CLANG_SUPPRESS_WARNING_POP
@@ -8,6 +8,14 @@

 #include "doctest_compatibility.h"

+// capture whether JSON_DELETE_DEPRECATED_FUNCTIONS was enabled on the command
+// line *before* including json.hpp, since the library #undefs it once the header
+// has been fully processed (see include/nlohmann/detail/macro_unscope.hpp); the
+// tests of deprecated functions are skipped if these functions are deleted
+#if defined(JSON_DELETE_DEPRECATED_FUNCTIONS) && (JSON_DELETE_DEPRECATED_FUNCTIONS == 1)
+    #define JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
+#endif
+
 #include <nlohmann/json.hpp>
 using nlohmann::json;

@@ -48,6 +56,7 @@ TEST_CASE("serialization")
        }
    }

+#ifndef JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
    SECTION("operator>>")
    {
        SECTION("no given width")
@@ -79,6 +88,7 @@ TEST_CASE("serialization")
                  "[\n\t\"foo\",\n\t1,\n\t2,\n\t3,\n\tfalse,\n\t{\n\t\t\"one\": 1\n\t}\n]");
        }
    }
+#endif

    SECTION("dump")
    {
@@ -15,6 +15,23 @@
 #include <nlohmann/json.hpp>
 using nlohmann::detail::dtoa_impl::reinterpret_bits;

+#include <array>
+#include <cmath>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+#include <iomanip>
+#include <limits>
+#include <locale>
+#include <random>
+#include <sstream>
+#include <string>
+#include <utility>
+#include <vector>
+#if defined(JSON_HAS_CPP_17)
+    #include <charconv>
+#endif
+
 namespace
 {
 float make_float(uint32_t sign_bit, uint32_t biased_exponent, uint32_t significand)
@@ -450,7 +467,7 @@ TEST_CASE("formatting")
        check_double(  1.2345e+18,   "1.2345e+18"             ); //  1.2345e+18                1.2345e+18                1.2345e18
        check_double(  1.2345e+19,   "1.2345e+19"             ); //  1.2345e+19                1.2345e+19                1.2345e19
        check_double(  1.2345e+20,   "1.2345e+20"             ); //  1.2345e+20                1.2345e+20                1.2345e20
-        check_double(  1.2345e+21,   "1.2344999999999999e+21" ); //  1.2345e+21                1.2344999999999999e+21    1.2345e21
+        check_double(  1.2345e+21,   "1.2345e+21"             ); //  1.2345e+21                1.2344999999999999e+21    1.2345e21
        check_double(  1.2345e+22,   "1.2345e+22"             ); //  1.2345e+22                1.2345e+22                1.2345e22
    }

@@ -514,3 +531,246 @@ TEST_CASE("formatting")
        check_integer(1000000000000000000LL, "1000000000000000000");
    }
 }
+
+namespace
+{
+// a small unsigned big integer (32-bit limbs, least significant first), to
+// recompute the powers of ten of the shortest double conversion
+using big = std::vector<std::uint32_t>;
+
+void big_mul_small(big& x, std::uint32_t m)
+{
+    std::uint64_t carry = 0;
+    for (auto& limb : x)
+    {
+        const std::uint64_t v = (static_cast<std::uint64_t>(limb) * m) + carry;
+        limb = static_cast<std::uint32_t>(v);
+        carry = v >> 32u;
+    }
+    if (carry != 0)
+    {
+        x.push_back(static_cast<std::uint32_t>(carry));
+    }
+}
+
+void big_div_small(big& x, std::uint32_t d)
+{
+    std::uint64_t rest = 0;
+    for (std::size_t i = x.size(); i-- > 0;)
+    {
+        const std::uint64_t v = (rest << 32u) | x[i];
+        x[i] = static_cast<std::uint32_t>(v / d);
+        rest = v % d;
+    }
+    while (!x.empty() && x.back() == 0)
+    {
+        x.pop_back();
+    }
+}
+
+std::size_t big_bit_length(const big& x)
+{
+    std::size_t n = 32 * x.size();
+    for (std::uint32_t top = x.back(); (top & 0x80000000u) == 0; top <<= 1u)
+    {
+        --n;
+    }
+    return n;
+}
+
+bool big_bit(const big& x, std::size_t i)
+{
+    return ((x[i / 32] >> (i % 32)) & 1u) != 0;
+}
+
+/// the 128 most significant bits of x (floor), shifted left if x has fewer bits
+std::pair<std::uint64_t, std::uint64_t> big_top128(const big& x)
+{
+    const std::size_t n = big_bit_length(x);
+    std::uint64_t high = 0;
+    std::uint64_t low = 0;
+    for (std::size_t k = 0; k < 128; ++k)
+    {
+        const bool bit = k < n && big_bit(x, n - 1 - k);
+        if (k < 64)
+        {
+            high = (high << 1u) | (bit ? 1u : 0u);
+        }
+        else
+        {
+            low = (low << 1u) | (bit ? 1u : 0u);
+        }
+    }
+    return {high, low};
+}
+
+/// the digits (without trailing zeros) and the decimal exponent of a
+/// representation "[-]d[.ddd][e[+-]x]"
+std::pair<std::string, int> digits_and_exponent(const std::string& s)
+{
+    std::string digits;
+    int point = -1;
+    int exponent = 0;
+    for (std::size_t i = 0; i < s.size(); ++i)
+    {
+        const char c = s[i];
+        if (c >= '0' && c <= '9')
+        {
+            digits += c;
+        }
+        else if (c == '.')
+        {
+            point = static_cast<int>(digits.size());
+        }
+        else if (c == 'e' || c == 'E')
+        {
+            exponent = std::stoi(s.substr(i + 1));
+            break;
+        }
+    }
+    int e = exponent + (point < 0 ? static_cast<int>(digits.size()) : point) - static_cast<int>(digits.size());
+    const std::size_t first = digits.find_first_not_of('0');
+    digits = first == std::string::npos ? "0" : digits.substr(first);
+    while (digits.size() > 1 && digits.back() == '0')
+    {
+        digits.pop_back();
+        ++e;
+    }
+    return {digits, e};
+}
+
+/// whether the decimal digits * 10^e reads back as v
+bool reads_back(const std::string& digits, int e, double v)
+{
+    const std::string text = digits + "e" + std::to_string(e);
+    // (compared bit for bit: v is positive and finite, and -Wfloat-equal)
+    return reinterpret_bits<std::uint64_t>(std::strtod(text.c_str(), nullptr)) == reinterpret_bits<std::uint64_t>(v);
+}
+
+/// Check the representation of a positive finite double: it reads back as
+/// the same value, and no representation with fewer digits does.
+void check_shortest(double v)
+{
+    std::array<char, 33> buf{};
+    char* end = nlohmann::detail::to_chars(buf.data(), buf.data() + 32, v);
+    const std::string text(buf.data(), end);
+    CAPTURE(text)
+    CHECK(std::strtod(text.c_str(), nullptr) == v);
+    // the layout is that of format_buffer() for the same digits
+    std::array<char, 64> reference{};
+    int len = 0;
+    int exponent = 0;
+    nlohmann::detail::dtoa_impl::shortest_digits(reference.data(), len, exponent, v);
+    const char* const reference_end = nlohmann::detail::dtoa_impl::format_buffer(reference.data(), len, exponent, -4, 15);
+    CHECK(text == std::string(reference.data(), static_cast<std::size_t>(reference_end - reference.data())));
+    const auto de = digits_and_exponent(text);
+    const std::string& digits = de.first;
+    if (digits.size() > 1)
+    {
+        // the decimals of one digit fewer next to the value
+        // (a stream rather than snprintf("%.*e"), whose output GCC cannot bound)
+        std::ostringstream shorter;
+        shorter.imbue(std::locale::classic());
+        shorter << std::scientific << std::setprecision(static_cast<int>(digits.size()) - 2) << v;
+        const auto near = digits_and_exponent(shorter.str());
+        // as an integer with digits.size() - 1 digits
+        std::string m = near.first;
+        int e = near.second;
+        while (m.size() < digits.size() - 1)
+        {
+            m += '0';
+            --e;
+        }
+        const std::uint64_t mid = std::stoull(m);
+        for (const std::uint64_t candidate :
+                {
+                    mid - 1, mid, mid + 1
+                })
+        {
+            CAPTURE(candidate)
+            CHECK(!reads_back(std::to_string(candidate), e, v));
+        }
+    }
+#if defined(JSON_HAS_CPP_17) && defined(__cpp_lib_to_chars)
+    // the closest of the shortest representations, as std::to_chars finds it
+    std::array<char, 64> std_text{};
+    const auto r = std::to_chars(std_text.data(), std_text.data() + std_text.size(), v, std::chars_format::scientific);
+    CHECK(digits_and_exponent(std::string(std_text.data(), r.ptr)) == de);
+#endif
+}
+} // namespace
+
+TEST_CASE("shortest digits of doubles")
+{
+    SECTION("powers of ten")
+    {
+        // the 128-bit significands of 10^k, rounded down, recomputed
+        for (int k = -342; k <= 341; ++k)
+        {
+            CAPTURE(k)
+            big x{1};
+            if (k >= 0)
+            {
+                for (int i = 0; i < k; ++i)
+                {
+                    big_mul_small(x, 10);
+                }
+            }
+            else
+            {
+                // floor(2^b / 10^-k) for a b that leaves more than 128 bits
+                const int b = 128 + 64 + (4 * -k);
+                x.assign(static_cast<std::size_t>(b / 32) + 1, 0);
+                x.back() = 1u << (b % 32);
+                for (int i = 0; i < -k; ++i)
+                {
+                    big_div_small(x, 10);
+                }
+            }
+            const auto expected = big_top128(x);
+            const auto actual = nlohmann::detail::zmij::pow10(k);
+            CHECK(actual.high == expected.first);
+            CHECK(actual.low == expected.second);
+        }
+    }
+
+    SECTION("boundary values")
+    {
+        for (const double v :
+                {
+                    std::numeric_limits<double>::min(), std::numeric_limits<double>::max(), std::numeric_limits<double>::denorm_min(),
+                    std::nextafter(std::numeric_limits<double>::min(), 0.0), 1.0, 2.0, 0.1, 0.3, 1e21, 1e22, 1e23, 5e-324, 9007199254740993.0,
+                    1.2345e+21, 2.2250738585072014e-308, 1.7976931348623157e308, 4.9406564584124654e-324, 123456789012345680.0
+                })
+        {
+            check_shortest(v);
+        }
+        // all powers of two (their rounding interval is narrower below)
+        for (int e = -1074; e <= 1023; ++e)
+        {
+            check_shortest(std::ldexp(1.0, e));
+        }
+        // powers of ten and their neighbors
+        for (int e = -323; e <= 308; ++e)
+        {
+            const double p = std::strtod(("1e" + std::to_string(e)).c_str(), nullptr);
+            check_shortest(p);
+            check_shortest(std::nextafter(p, 0.0));
+            check_shortest(std::nextafter(p, std::numeric_limits<double>::infinity()));
+        }
+    }
+
+    SECTION("random doubles")
+    {
+        std::mt19937_64 rng(5295); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed): reproducible
+        for (int i = 0; i < 100000; ++i)
+        {
+            const std::uint64_t bits = rng() & 0x7FFFFFFFFFFFFFFFu;
+            const auto v = reinterpret_bits<double>(bits);
+            if (std::isfinite(v) && bits != 0)
+            {
+                check_shortest(v);
+            }
+        }
+    }
+}
@@ -8,6 +8,14 @@

 #include "doctest_compatibility.h"

+// capture whether JSON_DELETE_DEPRECATED_FUNCTIONS was enabled on the command
+// line *before* including json.hpp, since the library #undefs it once the header
+// has been fully processed (see include/nlohmann/detail/macro_unscope.hpp); the
+// tests of deprecated functions are skipped if these functions are deleted
+#if defined(JSON_DELETE_DEPRECATED_FUNCTIONS) && (JSON_DELETE_DEPRECATED_FUNCTIONS == 1)
+    #define JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
+#endif
+
 #include <nlohmann/json.hpp>
 using nlohmann::json;

@@ -27,10 +35,59 @@ TEST_CASE("UBJSON")
    {
        SECTION("discarded")
        {
-            // discarded values are not serialized
+            // a discarded value cannot be serialized to UBJSON
            json const j = json::value_t::discarded;
-            const auto result = json::to_ubjson(j);
-            CHECK(result.empty());
+            CHECK_THROWS_WITH_AS(json::to_ubjson(j), "[json.exception.type_error.321] cannot serialize discarded value to UBJSON", json::type_error&);
+        }
+
+        SECTION("discarded values nested in a container")
+        {
+            json const discarded = json::value_t::discarded;
+
+            SECTION("in an array")
+            {
+                json const j = {1, discarded, 2};
+#if JSON_DIAGNOSTICS
+                CHECK_THROWS_WITH_AS(json::to_ubjson(j), "[json.exception.type_error.321] (/1) cannot serialize discarded value to UBJSON", json::type_error&);
+#else
+                CHECK_THROWS_WITH_AS(json::to_ubjson(j), "[json.exception.type_error.321] cannot serialize discarded value to UBJSON", json::type_error&);
+#endif
+            }
+
+            SECTION("as an object value")
+            {
+                json j;
+                j["a"] = 1;
+                j["b"] = discarded;
+#if JSON_DIAGNOSTICS
+                CHECK_THROWS_WITH_AS(json::to_ubjson(j), "[json.exception.type_error.321] (/b) cannot serialize discarded value to UBJSON", json::type_error&);
+#else
+                CHECK_THROWS_WITH_AS(json::to_ubjson(j), "[json.exception.type_error.321] cannot serialize discarded value to UBJSON", json::type_error&);
+#endif
+            }
+
+            SECTION("nested deeper (array in object in array)")
+            {
+                json inner_array = {1, discarded};
+                json middle_object;
+                middle_object["x"] = inner_array;
+                json const j = {middle_object};
+#if JSON_DIAGNOSTICS
+                CHECK_THROWS_WITH_AS(json::to_ubjson(j), "[json.exception.type_error.321] (/0/x/1) cannot serialize discarded value to UBJSON", json::type_error&);
+#else
+                CHECK_THROWS_WITH_AS(json::to_ubjson(j), "[json.exception.type_error.321] cannot serialize discarded value to UBJSON", json::type_error&);
+#endif
+            }
+
+            SECTION("optimized array of all-discarded elements")
+            {
+                json const j = {discarded, discarded};
+#if JSON_DIAGNOSTICS
+                CHECK_THROWS_WITH_AS(json::to_ubjson(j, true, true), "[json.exception.type_error.321] (/0) cannot serialize discarded value to UBJSON", json::type_error&);
+#else
+                CHECK_THROWS_WITH_AS(json::to_ubjson(j, true, true), "[json.exception.type_error.321] cannot serialize discarded value to UBJSON", json::type_error&);
+#endif
+            }
        }

        SECTION("null")
@@ -2091,9 +2148,14 @@ TEST_CASE("UBJSON")

        SECTION("discarded")
        {
+            // a discarded value cannot be serialized to UBJSON, even as part
+            // of an optimized array of a single (here: valueless) type
            json const j = {json::value_t::discarded, json::value_t::discarded};
-            std::vector<uint8_t> expected = {'[', '$', 'N', '#', 'i', 2};
-            CHECK(json::to_ubjson(j, true, true) == expected);
+#if JSON_DIAGNOSTICS
+            CHECK_THROWS_WITH_AS(json::to_ubjson(j, true, true), "[json.exception.type_error.321] (/0) cannot serialize discarded value to UBJSON", json::type_error&);
+#else
+            CHECK_THROWS_WITH_AS(json::to_ubjson(j, true, true), "[json.exception.type_error.321] cannot serialize discarded value to UBJSON", json::type_error&);
+#endif
        }
    }
 }
@@ -2212,8 +2274,10 @@ TEST_CASE("UBJSON input that cannot be read is discarded by every overload")
    CHECK_THROWS_AS(_ = json::from_ubjson(input.begin(), input.end()), json::parse_error&);
    CHECK(json::from_ubjson(input, true, false).is_discarded());
    CHECK(json::from_ubjson(input.begin(), input.end(), true, false).is_discarded());
+#ifndef JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
    CHECK(json::from_ubjson(input.data(), input.size(), true, false).is_discarded());
    CHECK(json::from_ubjson({input.data(), input.size()}, true, false).is_discarded());
+#endif
 }

 TEST_CASE("UBJSON SAX parsing stops at every event")
@@ -2961,12 +3025,14 @@ TEST_CASE("UBJSON roundtrips" * doctest::skip())
                CHECK(j1 == j2);
            }

+#ifndef JSON_TEST_DEPRECATED_FUNCTIONS_DELETED
            {
                INFO_WITH_TEMP(filename + ": uint8_t* and size");
                json j2;
                CHECK_NOTHROW(j2 = json::from_ubjson({packed.data(), packed.size()}));
                CHECK(j1 == j2);
            }
+#endif

            {
                INFO_WITH_TEMP(filename + ": output to output adapters");