text: //===----------------------------------------------------------------------===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef _LIBCPP___COMPARE_SYNTH_THREE_WAY_H
  #define _LIBCPP___COMPARE_SYNTH_THREE_WAY_H
  
  #include <__compare/ordering.h>
  #include <__compare/three_way_comparable.h>
  #include <__concepts/boolean_testable.h>
  #include <__config>
  #include <__utility/declval.h>
  
  #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  #pragma GCC system_header
  #endif
  
  _LIBCPP_BEGIN_NAMESPACE_STD
  
  #if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_CONCEPTS)
  
  // [expos.only.func]
  
  _LIBCPP_HIDE_FROM_ABI inline constexpr auto __synth_three_way =
    []<class _Tp, class _Up>(const _Tp& __t, const _Up& __u)
      requires requires {
        { __t < __u } -> __boolean_testable;
        { __u < __t } -> __boolean_testable;
      }
    {
      if constexpr (three_way_comparable_with<_Tp, _Up>) {
        return __t <=> __u;
      } else {
        if (__t < __u) return weak_ordering::less;
        if (__u < __t) return weak_ordering::greater;
        return weak_ordering::equivalent;
      }
    };
  
  template <class _Tp, class _Up = _Tp>
  using __synth_three_way_result = decltype(__synth_three_way(declval<_Tp&>(), declval<_Up&>()));
  
  #endif // _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_CONCEPTS)
  
  _LIBCPP_END_NAMESPACE_STD
  
  #endif // _LIBCPP___COMPARE_SYNTH_THREE_WAY_H
  