libcxx/include/__compare/compare_three_way_result.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_COMPARE_THREE_WAY_RESULT_H
  10 #define _LIBCPP___COMPARE_COMPARE_THREE_WAY_RESULT_H
  11
  12 #include <__config>
  13 #include <__type_traits/make_const_lvalue_ref.h>
  14 #include <__utility/declval.h>
  15
  16 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  17 #  pragma GCC system_header
  18 #endif
  19
  20 _LIBCPP_BEGIN_NAMESPACE_STD
  21
  22 #if _LIBCPP_STD_VER >= 20
  23
  24 template <class, class, class>
  25 struct _LIBCPP_HIDE_FROM_ABI __compare_three_way_result {};
  26
  27 template <class _Tp, class _Up>
  28 struct _LIBCPP_HIDE_FROM_ABI __compare_three_way_result<
  29     _Tp,
  30     _Up,
  31     decltype(std::declval<__make_const_lvalue_ref<_Tp>>() <=> std::declval<__make_const_lvalue_ref<_Up>>(), void())> {
  32   using type = decltype(std::declval<__make_const_lvalue_ref<_Tp>>() <=> std::declval<__make_const_lvalue_ref<_Up>>());
  33 };
  34
  35 template <class _Tp, class _Up = _Tp>
  36 struct _LIBCPP_TEMPLATE_VIS compare_three_way_result : __compare_three_way_result<_Tp, _Up, void> {};
  37
  38 template <class _Tp, class _Up = _Tp>
  39 using compare_three_way_result_t = typename compare_three_way_result<_Tp, _Up>::type;
  40
  41 #endif // _LIBCPP_STD_VER >= 20
  42
  43 _LIBCPP_END_NAMESPACE_STD
  44
  45 #endif // _LIBCPP___COMPARE_COMPARE_THREE_WAY_RESULT_H