Niels LohmannandClaude Sonnet 5.5 8d591bf720 Read iterator pairs of std::string and std::vector as pointer ranges (#6029) ...

* Read iterator pairs of std::string and std::vector as pointer ranges

Before C++20, a pair of iterators of a contiguous container cannot be told
from any other random-access iterator, so json::parse(s.begin(), s.end())
on a std::string or std::vector<char> was read one character at a time,
without the bulk scans of strings, numbers and indentation that the
container itself gets (the container overload of input_adapter() already
maps it to a pointer range). The iterators of std::string and of a
std::vector of 1-byte integral elements are now matched exactly and mapped
to the pointer range they cover; an empty range is not dereferenced. The
character type stays the same, so the results and error positions do not
change.

parse(first, last) of a std::string gets 1.7-2.0x as fast in C++17 on an
Apple M1 Max, accept(first, last) 2.7-3.1x, and from_cbor(first, last) of a
std::vector 8-23% faster.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Fix CI: clang-tidy, unused result, Infer false positive in tests

- unit-deserialization.cpp: raw string literals, and assign the result
  of parse() in CHECK_THROWS_AS (-Wunused-result)
- unit-bson.cpp: mark Infer's NULLPTR_DEREFERENCE on from_bson() with an
  iterator pair as a false positive

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Fix implicit char conversion in iterator-pair test

The test built std::vector<unsigned char> and <signed char> from a char
range, which -fsanitize=integer reports as an implicit conversion.

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
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
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>

* Iterator ranges: astyle-safe trait members; reserve in the test helper

The byte check and the container match are static constexpr members
instead of integral_constant arguments and a default template argument
with comparisons, which astyle spaced out.

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>

2026-11-10 22:30:31 +01:00

..

nlohmann

Read iterator pairs of std::string and std::vector as pointer ranges (#6029)

2026-11-10 22:30:31 +01:00