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* [gcc r14-10044] libstdc++: Simplify constraints on <=> for std::reference_wrapper
@ 2024-04-19 20:08 Jonathan Wakely
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From: Jonathan Wakely @ 2024-04-19 20:08 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:d86472a6f041ccf3d1be0cf6bb15d1e0ad8f6dbe
commit r14-10044-gd86472a6f041ccf3d1be0cf6bb15d1e0ad8f6dbe
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Fri Apr 19 17:42:04 2024 +0100
libstdc++: Simplify constraints on <=> for std::reference_wrapper
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.
Diff:
---
libstdc++-v3/include/bits/refwrap.h | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)
diff --git a/libstdc++-v3/include/bits/refwrap.h b/libstdc++-v3/include/bits/refwrap.h
index fd1cc2b63e6..71ec2b297b7 100644
--- a/libstdc++-v3/include/bits/refwrap.h
+++ b/libstdc++-v3/include/bits/refwrap.h
@@ -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
};
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