libcxx/include/__compare/compare_partial_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_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 <__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_partial_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::partial_order(std::forward<_Tp>(__t), std::forward<_Up>(__u))))
  35       -> decltype(std::partial_order(std::forward<_Tp>(__t), std::forward<_Up>(__u))) {
  36     return std::partial_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)  ? partial_ordering::equivalent
  43       : std::forward<_Tp>(__t) < std::forward<_Up>(__u) ? partial_ordering::less
  44       : std::forward<_Up>(__u) < std::forward<_Tp>(__t)
  45           ? partial_ordering::greater
  46           : partial_ordering::unordered))
  47       -> decltype(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)
  50                       ? partial_ordering::greater
  51                       : partial_ordering::unordered) {
  52     return std::forward<_Tp>(__t) == std::forward<_Up>(__u) ? partial_ordering::equivalent
  53          : std::forward<_Tp>(__t) < std::forward<_Up>(__u)  ? partial_ordering::less
  54          : std::forward<_Up>(__u) < std::forward<_Tp>(__t)
  55              ? partial_ordering::greater
  56              : partial_ordering::unordered;
  57   }
  58
  59   template <class _Tp, class _Up>
  60   _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t, _Up&& __u) const
  61       noexcept(noexcept(__go(std::forward<_Tp>(__t), std::forward<_Up>(__u), __priority_tag<1>())))
  62           -> decltype(__go(std::forward<_Tp>(__t), std::forward<_Up>(__u), __priority_tag<1>())) {
  63     return __go(std::forward<_Tp>(__t), std::forward<_Up>(__u), __priority_tag<1>());
  64   }
  65 };
  66 } // namespace __compare_partial_order_fallback
  67
  68 inline namespace __cpo {
  69 inline constexpr auto compare_partial_order_fallback = __compare_partial_order_fallback::__fn{};
  70 } // namespace __cpo
  71
  72 #endif // _LIBCPP_STD_VER >= 20
  73
  74 _LIBCPP_END_NAMESPACE_STD
  75
  76 #endif // _LIBCPP___COMPARE_COMPARE_PARTIAL_ORDER_FALLBACK