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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.
This commit is contained in:
Jonathan Wakely 2021-06-14 12:30:52 +01:00
parent e2c79b968f
commit b76a529c09
2 changed files with 13 additions and 3 deletions
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14
libstdc++-v3/libsupc++/compare
View File

@ -806,6 +806,16 @@ namespace std
}
};
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3465. compare_partial_order_fallback requires F < E
template<typename _Tp, typename _Up>
concept __op_eq_lt_lt = __op_eq_lt<_Tp, _Up>
&& requires(_Tp&& __t, _Up&& __u)
{
{ static_cast<_Up&&>(__u) < static_cast<_Tp&&>(__t) }
-> convertible_to<bool>;
};
class _Partial_fallback
{
template<typename _Tp, typename _Up>
@ -821,7 +831,7 @@ namespace std
public:
template<typename _Tp, __decayed_same_as<_Tp> _Up>
requires __partially_ordered<_Tp, _Up> || __op_eq_lt<_Tp, _Up>
requires __partially_ordered<_Tp, _Up> || __op_eq_lt_lt<_Tp, _Up>
constexpr partial_ordering
operator()(_Tp&& __e, _Up&& __f) const
noexcept(_S_noexcept<_Tp, _Up>())
@ -829,7 +839,7 @@ namespace std
if constexpr (__partially_ordered<_Tp, _Up>)
return _Partial_order{}(static_cast<_Tp&&>(__e),
static_cast<_Up&&>(__f));
else // __op_eq_lt<_Tp, _Up>
else // __op_eq_lt_lt<_Tp, _Up>
return static_cast<_Tp&&>(__e) == static_cast<_Up&&>(__f)
? partial_ordering::equivalent
: static_cast<_Tp&&>(__e) < static_cast<_Up&&>(__f)

2
libstdc++-v3/testsuite/18_support/comparisons/algorithms/fallback.cc
View File

@ -38,5 +38,5 @@ static_assert( has_weak_order_fallback<S, S> );
static_assert( has_weak_order_fallback<const S, S> );
static_assert( ! has_weak_order_fallback<const S, const S> );
static_assert( has_partial_order_fallback<S, S> );
static_assert( has_partial_order_fallback<const S, S> );
static_assert( ! has_partial_order_fallback<const S, S> ); // LWG 3465
static_assert( ! has_partial_order_fallback<const S, const S> );