libcxx/include/__compare/compare_weak_order_fallback.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_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]
  30 namespace __compare_weak_order_fallback {
  31 struct __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
  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