common_comparison_category.hpp

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// SPDX-License-Identifier: BSL-1.0
// SPDX-FileCopyrightText: Copyright (C) 2021 Tobias Hienzsch
 
#ifndef TETL_COMPARE_COMMON_COMPARISON_CATEGORY_HPP
#define TETL_COMPARE_COMMON_COMPARISON_CATEGORY_HPP
 
#include <etl/_compare/partial_ordering.hpp>
#include <etl/_compare/strong_ordering.hpp>
#include <etl/_compare/weak_ordering.hpp>
#include <etl/_type_traits/is_same.hpp>
 
namespace etl {
 
namespace detail {
 
template <unsigned>
struct common_cmpcat_base {
    using type = void;
};
 
template <>
struct common_cmpcat_base<0U> {
    using type = strong_ordering;
};
 
template <>
struct common_cmpcat_base<2U> {
    using type = partial_ordering;
};
 
template <>
struct common_cmpcat_base<4U> {
    using type = weak_ordering;
};
 
template <>
struct common_cmpcat_base<6U> {
    using type = partial_ordering;
};
 
} // namespace detail
 
/// \ingroup compare
template <typename... Ts>
struct common_comparison_category
    :
    // clang-format off
    detail::common_cmpcat_base<(0U | ... |
        (is_same_v<Ts, strong_ordering>  ? 0U :
         is_same_v<Ts, weak_ordering>    ? 4U :
         is_same_v<Ts, partial_ordering> ? 2U : 1U)
    )>
// clang-format on
{ };
 
/// \relates common_comparison_category
/// \ingroup compare
template <typename... Ts>
using common_comparison_category_t = typename common_comparison_category<Ts...>::type;
 
} // namespace etl
 
#endif // TETL_COMPARE_COMMON_COMPARISON_CATEGORY_HPP