Under C++20 P2468R2, a hand-written operator!= suppresses the compiler's
rewritten-candidate synthesis for operator==, preventing heterogeneous
comparisons like `std::string s; json j; s == j;` from compiling.
Fix by removing the hand-written operator!=, allowing the compiler to
synthesize != as !(a==b) in all language modes (C++20 member functions
and pre-C++20 friend functions).
Behavior change: operator!= now returns !(a==b) unconditionally, including
for special values like NaN and discarded. This means:
- NaN != NaN now returns true (matches IEEE-754 semantics)
- discarded != x now returns true for any x (matches !(discarded == x))
This also fixes underlying defects in previously-working code:
- Restores direct == comparison for views vs json (reverts std::ranges::equal
workaround added in PR #3950 to dodge this bug)
- Re-enables std::string == json comparisons (uncomments check in
unit-constructor1.cpp)
Fixes: #3868, #3979
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
* Add reference handling to tuples
Signed-off-by: Evelyn LePain <ava.lepain@gmail.com>
* Remove template template type because pair isn't working
Signed-off-by: Evelyn LePain <ava.lepain@gmail.com>
* amalgamate std::tie changes
Signed-off-by: Evelyn LePain <ava.lepain@gmail.com>
* allow the elation of a move by removing the ref requirement
Signed-off-by: Evelyn LePain <ava.lepain@gmail.com>
* force all number_xxx_t to be interchangeable
Signed-off-by: Evelyn LePain <ava.lepain@gmail.com>
* Finally got amalgamate to work correctly
Signed-off-by: Evelyn LePain <ava.lepain@gmail.com>
* remove const version, add a test case for scrambled number representations.
Signed-off-by: Evelyn LePain <ava.lepain@gmail.com>
* Use the logical set of requirements instead of decltype because VS 2015 doesn't like it
Signed-off-by: Evelyn LePain <ava.lepain@gmail.com>
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Signed-off-by: Evelyn LePain <ava.lepain@gmail.com>
Niels Lohmann
EALePain
Raphael Grimm
Florian Albrechtskirchinger