* Parse JSON in one block of memory with a fused pointer-based parser
The parser and the lexer exchange one token at a time, and the lexer keeps
its state (the current character, a pending unget, where the token starts)
in members, which every character pays for: json::accept() of twitter.json
took 2.8x as long as json_document::accept(). detail::contiguous_parser
reads text in one block of memory through a local pointer, with the
grammar, the whitespace and the tokens in one loop (after yyjson's reader),
and drives a SAX handler: parse()'s DOM handler, accept()'s handler, or the
user's handler of sax_parse(). It is used with the default options (no
callback, no comments, no trailing commas; sax_parse() with strict = true).
Errors are reported by the library parser, so the exception, its message and
its position stay the same. contiguous_parser stops at the token that the
library parser would reject, before reporting it, so the events up to the
error are the same; then:
- parse() runs the library parser with a handler that only reports the
error (json_sax_error_reporter), with the lexer of parse(), which is
instantiated anyway;
- sax_parse() runs it with a handler that forwards only parse_error() to
the user's handler (json_sax_error_forwarder), so no event arrives twice;
- accept() returns the verdict.
A handler that returns false stops the parse as before. An error at the end
of a large input costs parse() about 1.2x of what it cost before.
On an Apple M1 Max: accept() 1.6-2.0x as fast, parse() 10-16% faster,
ordered_json 11-16%, sax_parse() with a user's handler 1.36-1.46x, small
messages 12-22% (parse()) and 2.1-2.4x (accept()). On x86-64 (GCC 15,
Clang 21): accept() 1.6-1.9x, parse() 5-17%, ordered_json 12-19%,
sax_parse() 1.32-1.57x. A translation unit that parses a string compiles 3%
(-O0) and 9% (-O2) slower.
unit-contiguous_parser.cpp compares the contiguous path with the byte path
(std::list iterators) on corner cases, generated documents, their
truncations and mutations, deep nesting, and narrow number types: the same
values with the same number types and float bits, exception messages,
accept() verdicts and sax_parse() events.
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
* Fix CI: unused parameter without exceptions, cpplint, BUILD.bazel
- json_sax_error_reporter::parse_error: mark the exception unused, as
JSON_THROW does not use it with JSON_NOEXCEPTION
- unit-contiguous_parser.cpp: compare the exceptions of both paths only
when exceptions are enabled (invalid input aborted the test otherwise)
- silence cpplint's readability/braces false positives on the if
statements inside the parser's macros
- add contiguous_parser.hpp to BUILD.bazel
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
* accept(): skip digits without computing their value
accept() needs the value of a number only for a float whose exponent may
reach the largest value. skip_digits() finds the end of the digits without
the multiply-adds of accumulate_digits(), and once an 8-byte word fails the
digit test, the remaining loop needs no bounds check: a non-digit is in
that word. The value is computed afterwards for the rare floats that need
it.
accept() of canada.json: -16 % on Apple M1, -22 % with GCC 15 and -21 %
with Clang 21 on x86-64; files with many numbers -9 to -15 %.
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
* Tests: mark parser callback in unit-contiguous_parser noexcept
Fixes the -Werror=noexcept failure with GCC 26 (ci_test_standards_gcc (26)).
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N5NasEsrzHhSNouxSoEwqz
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
* Tests: sweep_allocator::construct() accepts pointers to const
Recent libc++ (emsdk latest) probes construct(const T*, const T&) in an
unevaluated context while checking for trivial copies; the static_cast to
void* in the noexcept specification then fails to compile.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N5NasEsrzHhSNouxSoEwqz
(cherry picked from commit 794bf70823c12a2a1cb2a8a95f34dfb6357746a8)
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
* Tests: guard sweep_allocator::construct() against const types instead of const_cast
The const_cast added in the previous commit is rejected by
cppcoreguidelines-pro-type-const-cast (clang-tidy). Make construct() not
viable for const U instead, which is what libc++ probes for.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N5NasEsrzHhSNouxSoEwqz
(cherry picked from commit de099fa607001b710862fd1bbecef3609c54cbc4)
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
* Fix CI: astyle and clang-tidy for sweep_allocator::construct()
astyle 3.4.13 reformats the enable_if<!...> default template argument
(Check amalgamation). Delete the const overload instead, which makes the
libc++ probe for const objects fail in the SFINAE context just the same
and needs no <type_traits>.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N5NasEsrzHhSNouxSoEwqz
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
* Contiguous parser: review fixes (wording, macros, diagnostic positions)
- "default parser" instead of "library parser" in comments and tests
- the three comments in json.hpp say the same thing
- current() replaces the repeated `p != end ? *p : 0`
- the backslashes of each macro are aligned
- the docs say that JSON_DIAGNOSTIC_POSITIONS turns the fast path off
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
---------
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Co-authored-by: Claude Sonnet 5.5 <noreply@anthropic.com>
* Split the json_view feature page into sub-pages
The single features/json_view.md page grew to ~600 lines covering eight
topics. Split it into features/json_view/ with an overview page and
pages for ownership and lifetime, differences from basic_json, reading
values, generic code, editing, and images.
The new differences page collects what was spread over several sections
("What is the same", "What is different", "Duplicate keys", and notes in
the conversion and serialization sections) under one summary table, and
adds the parts of the basic_json interface a view does not have. The
other pages now link to it instead of restating the rules.
Internal links across the documentation point to the new pages.
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
* Docs: fix stale comments and trim repeated text in json_view pages
- fig-jsonview.js/.css: point the header comments at the new pages
- reading.md: views' strings are valid as long as the document (and a
borrowed source text), as lifetime.md says
- reading.md, generic_code.md: link to differences.md instead of
restating the member-order and repeated-key rules
- differences.md: drop the third mention of ordering comparisons, name
rbegin()/rend() in the iterator row
- exceptions.md: link editable documents to editing.md
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
---------
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
