libcxx/include/__compare/synth_three_way.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_SYNTH_THREE_WAY_H
  10 #define _LIBCPP___COMPARE_SYNTH_THREE_WAY_H
  11
  12 #include <__compare/ordering.h>
  13 #include <__compare/three_way_comparable.h>
  14 #include <__concepts/boolean_testable.h>
  15 #include <__config>
  16 #include <__utility/declval.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 // [expos.only.func]
  27
  28 _LIBCPP_HIDE_FROM_ABI inline constexpr auto __synth_three_way = []<class _Tp, class _Up>(const _Tp& __t, const _Up& __u)
  29   requires requires {
  30     { __t < __u } -> __boolean_testable;
  31     { __u < __t } -> __boolean_testable;
  32   }
  33 {
  34   if constexpr (three_way_comparable_with<_Tp, _Up>) {
  35     return __t <=> __u;
  36   } else {
  37     if (__t < __u)
  38       return weak_ordering::less;
  39     if (__u < __t)
  40       return weak_ordering::greater;
  41     return weak_ordering::equivalent;
  42   }
  43 };
  44
  45 template <class _Tp, class _Up = _Tp>
  46 using __synth_three_way_result = decltype(std::__synth_three_way(std::declval<_Tp&>(), std::declval<_Up&>()));
  47
  48 #endif // _LIBCPP_STD_VER >= 20
  49
  50 _LIBCPP_END_NAMESPACE_STD
  51
  52 #endif // _LIBCPP___COMPARE_SYNTH_THREE_WAY_H