libcxx/include/__concepts/equality_comparable.h

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef _LIBCPP___CONCEPTS_EQUALITY_COMPARABLE_H
  10 #define _LIBCPP___CONCEPTS_EQUALITY_COMPARABLE_H
  11
  12 #include <__concepts/boolean_testable.h>
  13 #include <__concepts/common_reference_with.h>
  14 #include <__config>
  15 #include <__type_traits/common_reference.h>
  16 #include <__type_traits/make_const_lvalue_ref.h>
  17
  18 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  19 #  pragma GCC system_header
  20 #endif
  21
  22 _LIBCPP_BEGIN_NAMESPACE_STD
  23
  24 #if _LIBCPP_STD_VER >= 20
  25
  26 // [concept.equalitycomparable]
  27
  28 template <class _Tp, class _Up>
  29 concept __weakly_equality_comparable_with =
  30     requires(__make_const_lvalue_ref<_Tp> __t, __make_const_lvalue_ref<_Up> __u) {
  31       { __t == __u } -> __boolean_testable;
  32       { __t != __u } -> __boolean_testable;
  33       { __u == __t } -> __boolean_testable;
  34       { __u != __t } -> __boolean_testable;
  35     };
  36
  37 template <class _Tp>
  38 concept equality_comparable = __weakly_equality_comparable_with<_Tp, _Tp>;
  39
  40 // clang-format off
  41 template <class _Tp, class _Up>
  42 concept equality_comparable_with =
  43     equality_comparable<_Tp> && equality_comparable<_Up> &&
  44     common_reference_with<__make_const_lvalue_ref<_Tp>, __make_const_lvalue_ref<_Up>> &&
  45     equality_comparable<
  46         common_reference_t<
  47             __make_const_lvalue_ref<_Tp>,
  48             __make_const_lvalue_ref<_Up>>> &&
  49     __weakly_equality_comparable_with<_Tp, _Up>;
  50 // clang-format on
  51
  52 #endif // _LIBCPP_STD_VER >= 20
  53
  54 _LIBCPP_END_NAMESPACE_STD
  55
  56 #endif // _LIBCPP___CONCEPTS_EQUALITY_COMPARABLE_H