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 // TODO MODULES restore the lamba to match the Standard.
  29 // See https://github.com/llvm/llvm-project/issues/57222
  30 //_LIBCPP_HIDE_FROM_ABI inline constexpr auto __synth_three_way =
  31 //  []<class _Tp, class _Up>(const _Tp& __t, const _Up& __u)
  32 template <class _Tp, class _Up>
  33 _LIBCPP_HIDE_FROM_ABI constexpr auto __synth_three_way(const _Tp& __t, const _Up& __u)
  34   requires requires {
  35     { __t < __u } -> __boolean_testable;
  36     { __u < __t } -> __boolean_testable;
  37   }
  38 {
  39   if constexpr (three_way_comparable_with<_Tp, _Up>) {
  40     return __t <=> __u;
  41   } else {
  42     if (__t < __u)
  43       return weak_ordering::less;
  44     if (__u < __t)
  45       return weak_ordering::greater;
  46     return weak_ordering::equivalent;
  47   }
  48 }
  49
  50 template <class _Tp, class _Up = _Tp>
  51 using __synth_three_way_result = decltype(std::__synth_three_way(std::declval<_Tp&>(), std::declval<_Up&>()));
  52
  53 #endif // _LIBCPP_STD_VER >= 20
  54
  55 _LIBCPP_END_NAMESPACE_STD
  56
  57 #endif // _LIBCPP___COMPARE_SYNTH_THREE_WAY_H