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_PARTIAL_ORDER_FALLBACK
10#define _LIBCPP___COMPARE_COMPARE_PARTIAL_ORDER_FALLBACK
11
12#include <__compare/ordering.h>
13#include <__compare/partial_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_partial_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::partial_order(std::forward<_Tp>(__t), std::forward<_Up>(__u))))
36      -> decltype(std::partial_order(std::forward<_Tp>(__t), std::forward<_Up>(__u))) {
37    return std::partial_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      { std::forward<_Up>(__u) < std::forward<_Tp>(__t) } -> __boolean_testable;
45    }
46  _LIBCPP_HIDE_FROM_ABI static constexpr partial_ordering __go(_Tp&& __t, _Up&& __u, __priority_tag<0>) noexcept(
47      noexcept(std::forward<_Tp>(__t) == std::forward<_Up>(__u)  ? partial_ordering::equivalent
48               : std::forward<_Tp>(__t) < std::forward<_Up>(__u) ? partial_ordering::less
49               : std::forward<_Up>(__u) < std::forward<_Tp>(__t) ? partial_ordering::greater
50                                                                 : partial_ordering::unordered)) {
51    return std::forward<_Tp>(__t) == std::forward<_Up>(__u) ? partial_ordering::equivalent
52         : std::forward<_Tp>(__t) < std::forward<_Up>(__u)  ? partial_ordering::less
53         : std::forward<_Up>(__u) < std::forward<_Tp>(__t)
54             ? partial_ordering::greater
55             : partial_ordering::unordered;
56  }
57
58  template <class _Tp, class _Up>
59  _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t, _Up&& __u) const
60      noexcept(noexcept(__go(std::forward<_Tp>(__t), std::forward<_Up>(__u), __priority_tag<1>())))
61          -> decltype(__go(std::forward<_Tp>(__t), std::forward<_Up>(__u), __priority_tag<1>())) {
62    return __go(std::forward<_Tp>(__t), std::forward<_Up>(__u), __priority_tag<1>());
63  }
64};
65} // namespace __compare_partial_order_fallback
66
67inline namespace __cpo {
68inline constexpr auto compare_partial_order_fallback = __compare_partial_order_fallback::__fn{};
69} // namespace __cpo
70
71#endif // _LIBCPP_STD_VER >= 20
72
73_LIBCPP_END_NAMESPACE_STD
74
75#endif // _LIBCPP___COMPARE_COMPARE_PARTIAL_ORDER_FALLBACK