libcxx/include/__compare/common_comparison_category.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_COMMON_COMPARISON_CATEGORY_H
  10 #define _LIBCPP___COMPARE_COMMON_COMPARISON_CATEGORY_H
  11
  12 #include <__compare/ordering.h>
  13 #include <__config>
  14 #include <__cstddef/size_t.h>
  15 #include <__type_traits/is_same.h>
  16
  17 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  18 #  pragma GCC system_header
  19 #endif
  20
  21 _LIBCPP_BEGIN_NAMESPACE_STD
  22
  23 #if _LIBCPP_STD_VER >= 20
  24
  25 namespace __comp_detail {
  26
  27 enum _ClassifyCompCategory : unsigned { _None, _PartialOrd, _WeakOrd, _StrongOrd, _CCC_Size };
  28
  29 template <class _Tp>
  30 _LIBCPP_HIDE_FROM_ABI constexpr _ClassifyCompCategory __type_to_enum() noexcept {
  31   if (is_same_v<_Tp, partial_ordering>)
  32     return _PartialOrd;
  33   if (is_same_v<_Tp, weak_ordering>)
  34     return _WeakOrd;
  35   if (is_same_v<_Tp, strong_ordering>)
  36     return _StrongOrd;
  37   return _None;
  38 }
  39
  40 template <size_t _Size>
  41 _LIBCPP_HIDE_FROM_ABI constexpr _ClassifyCompCategory
  42 __compute_comp_type(const _ClassifyCompCategory (&__types)[_Size]) {
  43   int __seen[_CCC_Size] = {};
  44   for (auto __type : __types)
  45     ++__seen[__type];
  46   if (__seen[_None])
  47     return _None;
  48   if (__seen[_PartialOrd])
  49     return _PartialOrd;
  50   if (__seen[_WeakOrd])
  51     return _WeakOrd;
  52   return _StrongOrd;
  53 }
  54
  55 template <class... _Ts, bool _False = false>
  56 _LIBCPP_HIDE_FROM_ABI constexpr auto __get_comp_type() {
  57   using _CCC                    = _ClassifyCompCategory;
  58   constexpr _CCC __type_kinds[] = {_StrongOrd, __type_to_enum<_Ts>()...};
  59   constexpr _CCC __cat          = __comp_detail::__compute_comp_type(__type_kinds);
  60   if constexpr (__cat == _None)
  61     return void();
  62   else if constexpr (__cat == _PartialOrd)
  63     return partial_ordering::equivalent;
  64   else if constexpr (__cat == _WeakOrd)
  65     return weak_ordering::equivalent;
  66   else if constexpr (__cat == _StrongOrd)
  67     return strong_ordering::equivalent;
  68   else
  69     static_assert(_False, "unhandled case");
  70 }
  71 } // namespace __comp_detail
  72
  73 // [cmp.common], common comparison category type
  74 template <class... _Ts>
  75 struct _LIBCPP_TEMPLATE_VIS common_comparison_category {
  76   using type = decltype(__comp_detail::__get_comp_type<_Ts...>());
  77 };
  78
  79 template <class... _Ts>
  80 using common_comparison_category_t = typename common_comparison_category<_Ts...>::type;
  81
  82 #endif // _LIBCPP_STD_VER >= 20
  83
  84 _LIBCPP_END_NAMESPACE_STD
  85
  86 #endif // _LIBCPP___COMPARE_COMMON_COMPARISON_CATEGORY_H