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libstdc++: Simplify constraints on <=> for std::reference_wrapper

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Instead of constraining these overloads in terms of synth-three-way we
can just check that the value_type is less-than-comparable, which is
what synth-three-way's constraints check.

The reason that I implemented these with constraints has now been filed
as LWG 4071, so add a comment about that too.

libstdc++-v3/ChangeLog:

	* include/bits/refwrap.h (operator<=>): Simplify constraints.
This commit is contained in:
Jonathan Wakely 2024-04-19 17:42:04 +01:00
parent eed7fb1b2f
commit d86472a6f0
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1 changed files with 11 additions and 5 deletions
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16
libstdc++-v3/include/bits/refwrap.h
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@ -384,23 +384,29 @@ _GLIBCXX_MEM_FN_TRAITS(&& noexcept, false_type, true_type)
&& requires { { __x.get() == __y.get() } -> convertible_to<bool>; }
{ return __x.get() == __y.get(); }
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 4071. reference_wrapper comparisons are not SFINAE-friendly
[[nodiscard]]
friend constexpr auto
operator<=>(reference_wrapper __x, reference_wrapper<_Tp> __y)
requires requires { __detail::__synth3way(__x.get(), __y.get()); }
operator<=>(reference_wrapper __x, reference_wrapper __y)
requires requires (const _Tp __t) {
{ __t < __t } -> __detail::__boolean_testable;
}
{ return __detail::__synth3way(__x.get(), __y.get()); }
[[nodiscard]]
friend constexpr auto
operator<=>(reference_wrapper __x, const _Tp& __y)
requires requires { __detail::__synth3way(__x.get(), __y); }
requires requires { { __y < __y } -> __detail::__boolean_testable; }
{ return __detail::__synth3way(__x.get(), __y); }
[[nodiscard]]
friend constexpr auto
operator<=>(reference_wrapper __x, reference_wrapper<const _Tp> __y)
requires (!is_const_v<_Tp>)
&& requires { __detail::__synth3way(__x.get(), __y.get()); }
requires (!is_const_v<_Tp>) && requires (const _Tp __t) {
{ __t < __t } -> __detail::__boolean_testable;
}
{ return __detail::__synth3way(__x.get(), __y.get()); }
#endif
};