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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
76

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source code of libcxx/include/__compare/compare_partial_order_fallback.h