libcxx/include/__compare/three_way_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___COMPARE_THREE_WAY_COMPARABLE_H
  10 #define _LIBCPP___COMPARE_THREE_WAY_COMPARABLE_H
  11
  12 #include <__compare/common_comparison_category.h>
  13 #include <__compare/ordering.h>
  14 #include <__concepts/common_reference_with.h>
  15 #include <__concepts/equality_comparable.h>
  16 #include <__concepts/same_as.h>
  17 #include <__concepts/totally_ordered.h>
  18 #include <__config>
  19 #include <__type_traits/common_reference.h>
  20 #include <__type_traits/make_const_lvalue_ref.h>
  21
  22 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  23 #  pragma GCC system_header
  24 #endif
  25
  26 _LIBCPP_BEGIN_NAMESPACE_STD
  27
  28 #if _LIBCPP_STD_VER >= 20
  29
  30 template <class _Tp, class _Cat>
  31 concept __compares_as = same_as<common_comparison_category_t<_Tp, _Cat>, _Cat>;
  32
  33 template <class _Tp, class _Cat = partial_ordering>
  34 concept three_way_comparable =
  35     __weakly_equality_comparable_with<_Tp, _Tp> && __partially_ordered_with<_Tp, _Tp> &&
  36     requires(__make_const_lvalue_ref<_Tp> __a, __make_const_lvalue_ref<_Tp> __b) {
  37       { __a <=> __b } -> __compares_as<_Cat>;
  38     };
  39
  40 template <class _Tp, class _Up, class _Cat = partial_ordering>
  41 concept three_way_comparable_with =
  42     three_way_comparable<_Tp, _Cat> && three_way_comparable<_Up, _Cat> &&
  43     common_reference_with<__make_const_lvalue_ref<_Tp>, __make_const_lvalue_ref<_Up>> &&
  44     three_way_comparable<common_reference_t<__make_const_lvalue_ref<_Tp>, __make_const_lvalue_ref<_Up>>, _Cat> &&
  45     __weakly_equality_comparable_with<_Tp, _Up> && __partially_ordered_with<_Tp, _Up> &&
  46     requires(__make_const_lvalue_ref<_Tp> __t, __make_const_lvalue_ref<_Up> __u) {
  47       { __t <=> __u } -> __compares_as<_Cat>;
  48       { __u <=> __t } -> __compares_as<_Cat>;
  49     };
  50
  51 #endif // _LIBCPP_STD_VER >= 20
  52
  53 _LIBCPP_END_NAMESPACE_STD
  54
  55 #endif // _LIBCPP___COMPARE_THREE_WAY_COMPARABLE_H