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 <__config>
15 #include <__type_traits/decay.h>
16 #include <__type_traits/is_same.h>
17 #include <__utility/forward.h>
18 #include <__utility/priority_tag.h>
19 
20 #ifndef _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER
21 #  pragma GCC system_header
22 #endif
23 
24 _LIBCPP_BEGIN_NAMESPACE_STD
25 
26 #if _LIBCPP_STD_VER >= 20
27 
28 // [cmp.alg]
29 namespace __compare_weak_order_fallback {
30 struct __fn {
31   template <class _Tp, class _Up>
32     requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
33   _LIBCPP_HIDE_FROM_ABI static constexpr auto __go(_Tp&& __t, _Up&& __u, __priority_tag<1>) noexcept(
34       noexcept(std::weak_order(std::forward<_Tp>(__t), std::forward<_Up>(__u))))
35       -> decltype(std::weak_order(std::forward<_Tp>(__t), std::forward<_Up>(__u))) {
36     return std::weak_order(std::forward<_Tp>(__t), std::forward<_Up>(__u));
37   }
38 
39   template <class _Tp, class _Up>
40     requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
41   _LIBCPP_HIDE_FROM_ABI static constexpr auto __go(_Tp&& __t, _Up&& __u, __priority_tag<0>) noexcept(noexcept(
42       std::forward<_Tp>(__t) == std::forward<_Up>(__u) ? weak_ordering::equivalent
43       : std::forward<_Tp>(__t) < std::forward<_Up>(__u)
44           ? weak_ordering::less
45           : weak_ordering::greater))
46       -> decltype(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 
65 inline namespace __cpo {
66 inline 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
74