@@ -481,13 +481,14 @@ namespace std
// BUILTIN-PTR-THREE-WAY(T, U)
template<typename _Tp, typename _Up>
concept __3way_builtin_ptr_cmp
- = three_way_comparable_with<_Tp, _Up>
+ = requires(_Tp&& __t, _Up&& __u)
+ { static_cast<_Tp&&>(__t) <=> static_cast<_Up&&>(__u); }
&& convertible_to<_Tp, const volatile void*>
&& convertible_to<_Up, const volatile void*>
&& ! requires(_Tp&& __t, _Up&& __u)
- { operator<=>(static_cast<_Tp&&>(__t), static_cast<_Up&&>(__u)); }
+ { operator<=>(static_cast<_Tp&&>(__t), static_cast<_Up&&>(__u)); }
&& ! requires(_Tp&& __t, _Up&& __u)
- { static_cast<_Tp&&>(__t).operator<=>(static_cast<_Up&&>(__u)); };
+ { static_cast<_Tp&&>(__t).operator<=>(static_cast<_Up&&>(__u)); };
} // namespace __detail
// [cmp.object], typename compare_three_way
@@ -495,6 +496,7 @@ namespace std
{
template<typename _Tp, typename _Up>
requires three_way_comparable_with<_Tp, _Up>
+ || __detail::__3way_builtin_ptr_cmp<_Tp, _Up>
constexpr auto
operator()(_Tp&& __t, _Up&& __u) const
noexcept(noexcept(std::declval<_Tp>() <=> std::declval<_Up>()))
new file mode 100644
@@ -0,0 +1,45 @@
+// Copyright (C) 2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library. This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3. If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <compare>
+
+void
+test01()
+{
+ struct X
+ {
+ operator int() const { return 0; }
+ operator long*() const { return nullptr; }
+ } x;
+
+ // Not three-way-comparable because of ambiguous conversion to int or long*:
+ static_assert( ! std::three_way_comparable<X> );
+
+ // And therefore X is not three-way-comparable-with anything else
+ // (because std::three_way_comparable_with<X, Y> requires that both
+ // three_way_comparable<X> and three_way_comparable<Y> are true).
+ static_assert( ! std::three_way_comparable_with<X, long*> );
+
+ long l;
+ // But <=> is valid and resolves to a builtin operator comparing pointers:
+ auto c = &l <=> x;
+ // So std::compare_three_way should be usable:
+ auto c2 = std::compare_three_way()(&l, x);
+}