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>
  16
  17 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  18 #pragma GCC system_header
  19 #endif
  20
  21 _LIBCPP_BEGIN_NAMESPACE_STD
  22
  23 #if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_CONCEPTS)
  24
  25 // [concept.equalitycomparable]
  26
  27 template<class _Tp, class _Up>
  28 concept __weakly_equality_comparable_with =
  29   requires(__make_const_lvalue_ref<_Tp> __t, __make_const_lvalue_ref<_Up> __u) {
  30     { __t == __u } -> __boolean_testable;
  31     { __t != __u } -> __boolean_testable;
  32     { __u == __t } -> __boolean_testable;
  33     { __u != __t } -> __boolean_testable;
  34   };
  35
  36 template<class _Tp>
  37 concept equality_comparable = __weakly_equality_comparable_with<_Tp, _Tp>;
  38
  39 template<class _Tp, class _Up>
  40 concept equality_comparable_with =
  41   equality_comparable<_Tp> && equality_comparable<_Up> &&
  42   common_reference_with<__make_const_lvalue_ref<_Tp>, __make_const_lvalue_ref<_Up>> &&
  43   equality_comparable<
  44     common_reference_t<
  45       __make_const_lvalue_ref<_Tp>,
  46       __make_const_lvalue_ref<_Up>>> &&
  47   __weakly_equality_comparable_with<_Tp, _Up>;
  48
  49 #endif // _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_CONCEPTS)
  50
  51 _LIBCPP_END_NAMESPACE_STD
  52
  53 #endif // _LIBCPP___CONCEPTS_EQUALITY_COMPARABLE_H