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 <__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