libstdc++: Implement LWG 3465 for std::compare_partial_order_fallback [PR101056]
libstdc++-v3/ChangeLog: PR libstdc++/101056 * libsupc++/compare (compare_partial_order_fallback): Add constraint using reversed parameter order, as per LWG 3465. * testsuite/18_support/comparisons/algorithms/fallback.cc: Adjust expected result.
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@ -806,6 +806,16 @@ namespace std
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}
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};
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// _GLIBCXX_RESOLVE_LIB_DEFECTS
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// 3465. compare_partial_order_fallback requires F < E
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template<typename _Tp, typename _Up>
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concept __op_eq_lt_lt = __op_eq_lt<_Tp, _Up>
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&& requires(_Tp&& __t, _Up&& __u)
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{
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{ static_cast<_Up&&>(__u) < static_cast<_Tp&&>(__t) }
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-> convertible_to<bool>;
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};
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class _Partial_fallback
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{
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template<typename _Tp, typename _Up>
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@ -821,7 +831,7 @@ namespace std
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public:
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template<typename _Tp, __decayed_same_as<_Tp> _Up>
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requires __partially_ordered<_Tp, _Up> || __op_eq_lt<_Tp, _Up>
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requires __partially_ordered<_Tp, _Up> || __op_eq_lt_lt<_Tp, _Up>
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constexpr partial_ordering
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operator()(_Tp&& __e, _Up&& __f) const
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noexcept(_S_noexcept<_Tp, _Up>())
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@ -829,7 +839,7 @@ namespace std
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if constexpr (__partially_ordered<_Tp, _Up>)
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return _Partial_order{}(static_cast<_Tp&&>(__e),
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static_cast<_Up&&>(__f));
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else // __op_eq_lt<_Tp, _Up>
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else // __op_eq_lt_lt<_Tp, _Up>
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return static_cast<_Tp&&>(__e) == static_cast<_Up&&>(__f)
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? partial_ordering::equivalent
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: static_cast<_Tp&&>(__e) < static_cast<_Up&&>(__f)
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@ -38,5 +38,5 @@ static_assert( has_weak_order_fallback<S, S> );
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static_assert( has_weak_order_fallback<const S, S> );
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static_assert( ! has_weak_order_fallback<const S, const S> );
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static_assert( has_partial_order_fallback<S, S> );
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static_assert( has_partial_order_fallback<const S, S> );
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static_assert( ! has_partial_order_fallback<const S, S> ); // LWG 3465
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static_assert( ! has_partial_order_fallback<const S, const S> );
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