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_WEAK_ORDER_FALLBACK
10#define _LIBCPP___COMPARE_COMPARE_WEAK_ORDER_FALLBACK
11
12#include <__compare/ordering.h>
13#include <__compare/weak_order.h>
14#include <__concepts/boolean_testable.h>
15#include <__config>
16#include <__type_traits/decay.h>
17#include <__type_traits/is_same.h>
18#include <__utility/forward.h>
19#include <__utility/priority_tag.h>
20
21#ifndef _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER
22#  pragma GCC system_header
23#endif
24
25_LIBCPP_BEGIN_NAMESPACE_STD
26
27#if _LIBCPP_STD_VER >= 20
28
29// [cmp.alg]
30namespace __compare_weak_order_fallback {
31struct __fn {
32  template <class _Tp, class _Up>
33    requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
34  _LIBCPP_HIDE_FROM_ABI static constexpr auto __go(_Tp&& __t, _Up&& __u, __priority_tag<1>) noexcept(
35      noexcept(std::weak_order(std::forward<_Tp>(__t), std::forward<_Up>(__u))))
36      -> decltype(std::weak_order(std::forward<_Tp>(__t), std::forward<_Up>(__u))) {
37    return std::weak_order(std::forward<_Tp>(__t), std::forward<_Up>(__u));
38  }
39
40  template <class _Tp, class _Up>
41    requires is_same_v<decay_t<_Tp>, decay_t<_Up>> && requires(_Tp&& __t, _Up&& __u) {
42      { std::forward<_Tp>(__t) == std::forward<_Up>(__u) } -> __boolean_testable;
43      { std::forward<_Tp>(__t) < std::forward<_Up>(__u) } -> __boolean_testable;
44    }
45  _LIBCPP_HIDE_FROM_ABI static constexpr weak_ordering __go(_Tp&& __t, _Up&& __u, __priority_tag<0>) noexcept(noexcept(
46      std::forward<_Tp>(__t) == std::forward<_Up>(__u) ? weak_ordering::equivalent
47      : std::forward<_Tp>(__t) < std::forward<_Up>(__u)
48          ? weak_ordering::less
49          : weak_ordering::greater)) {
50    return std::forward<_Tp>(__t) == std::forward<_Up>(__u) ? weak_ordering::equivalent
51         : std::forward<_Tp>(__t) < std::forward<_Up>(__u)
52             ? weak_ordering::less
53             : weak_ordering::greater;
54  }
55
56  template <class _Tp, class _Up>
57  _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t, _Up&& __u) const
58      noexcept(noexcept(__go(std::forward<_Tp>(__t), std::forward<_Up>(__u), __priority_tag<1>())))
59          -> decltype(__go(std::forward<_Tp>(__t), std::forward<_Up>(__u), __priority_tag<1>())) {
60    return __go(std::forward<_Tp>(__t), std::forward<_Up>(__u), __priority_tag<1>());
61  }
62};
63} // namespace __compare_weak_order_fallback
64
65inline namespace __cpo {
66inline constexpr auto compare_weak_order_fallback = __compare_weak_order_fallback::__fn{};
67} // namespace __cpo
68
69#endif // _LIBCPP_STD_VER >= 20
70
71_LIBCPP_END_NAMESPACE_STD
72
73#endif // _LIBCPP___COMPARE_COMPARE_WEAK_ORDER_FALLBACK