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Move the user-defined string literals to <nlohmann/json_literals.hpp>

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Following the review in #5294, the literals now live in their own header
instead of being removed entirely: <nlohmann/json.hpp> includes it at the
end unless JSON_NO_AUTOMATIC_UDLS (renamed from JSON_NO_UDLS) is defined,
so a project can opt out globally and include the header only where the
literals are used.

The header only uses public and standard macros, because the library's
internal macros are undefined at the end of json.hpp and the amalgamation
inlines macro_scope.hpp only once. For the same reason, the library no
longer defines and undefines JSON_USE_GLOBAL_UDLS, so a user's definition
is still visible to the header. The single-header copy is identical to
the multi-header one, as it only includes <nlohmann/json.hpp>. The module
always exports the literals.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann committed 2026-09-28 21:49:37 +02:00
1 parent e0ee07fe73
commit 1419aeff60
23 files changed
+418 -233
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include/nlohmann/json.hpp
+8 -62
View File
@@ -6423,57 +6423,6 @@ std::string format_as(const NLOHMANN_BASIC_JSON_TPL& j)
return j.dump();
}
#ifndef JSON_NO_UDLS
inline namespace literals
{
inline namespace json_literals
{
/// @brief user-defined string literal for JSON values
/// @sa https://json.nlohmann.me/api/basic_json/operator_literal_json/
JSON_HEDLEY_NON_NULL(1)
#if !defined(JSON_HEDLEY_GCC_VERSION) || JSON_HEDLEY_GCC_VERSION_CHECK(4,9,0)
inline nlohmann::json operator""_json(const char* s, std::size_t n)
#else
// GCC 4.8 requires a space between "" and suffix
inline nlohmann::json operator"" _json(const char* s, std::size_t n)
#endif
{
return nlohmann::json::parse(s, s + n);
}
#if defined(__cpp_char8_t)
JSON_HEDLEY_NON_NULL(1)
inline nlohmann::json operator""_json(const char8_t* s, std::size_t n)
{
return nlohmann::json::parse(reinterpret_cast<const char*>(s),
reinterpret_cast<const char*>(s) + n);
}
#endif
/// @brief user-defined string literal for JSON pointer
/// @sa https://json.nlohmann.me/api/basic_json/operator_literal_json_pointer/
JSON_HEDLEY_NON_NULL(1)
#if !defined(JSON_HEDLEY_GCC_VERSION) || JSON_HEDLEY_GCC_VERSION_CHECK(4,9,0)
inline nlohmann::json::json_pointer operator""_json_pointer(const char* s, std::size_t n)
#else
// GCC 4.8 requires a space between "" and suffix
inline nlohmann::json::json_pointer operator"" _json_pointer(const char* s, std::size_t n)
#endif
{
return nlohmann::json::json_pointer(std::string(s, n));
}
#if defined(__cpp_char8_t)
inline nlohmann::json::json_pointer operator""_json_pointer(const char8_t* s, std::size_t n)
{
return nlohmann::json::json_pointer(std::string(reinterpret_cast<const char*>(s), n));
}
#endif
} // namespace json_literals
} // namespace literals
#endif // JSON_NO_UDLS
NLOHMANN_JSON_NAMESPACE_END
///////////////////////
@@ -6608,17 +6557,6 @@ struct formatter<nlohmann::NLOHMANN_BASIC_JSON_TPL, char> // NOLINT(cert-dcl58-c
} // namespace std
#if JSON_USE_GLOBAL_UDLS && !defined(JSON_NO_UDLS)
#if !defined(JSON_HEDLEY_GCC_VERSION) || JSON_HEDLEY_GCC_VERSION_CHECK(4,9,0)
using nlohmann::literals::json_literals::operator""_json; // NOLINT(misc-unused-using-decls,google-global-names-in-headers)
using nlohmann::literals::json_literals::operator""_json_pointer; //NOLINT(misc-unused-using-decls,google-global-names-in-headers)
#else
// GCC 4.8 requires a space between "" and suffix
using nlohmann::literals::json_literals::operator"" _json; // NOLINT(misc-unused-using-decls,google-global-names-in-headers)
using nlohmann::literals::json_literals::operator"" _json_pointer; //NOLINT(misc-unused-using-decls,google-global-names-in-headers)
#endif
#endif
#include <nlohmann/detail/macro_unscope.hpp>
// End of GCC diagnostic pragmas for C++ modules support
@@ -6626,4 +6564,12 @@ struct formatter<nlohmann::NLOHMANN_BASIC_JSON_TPL, char> // NOLINT(cert-dcl58-c
#pragma GCC diagnostic pop
#endif
// The user-defined string literals are in a separate header, because their
// bodies instantiate the parser in every translation unit that includes them.
// Define JSON_NO_AUTOMATIC_UDLS to include <nlohmann/json_literals.hpp> only
// where needed.
#ifndef JSON_NO_AUTOMATIC_UDLS
#include <nlohmann/json_literals.hpp>
#endif
#endif // INCLUDE_NLOHMANN_JSON_HPP_