is_weakly_decrementable.hpp

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//
//  CeresEngine - A game development framework
//
//  Created by Rogiel Sulzbach.
//  Copyright (c) 2018-2022 Rogiel Sulzbach. All rights reserved.
//
 
#pragma once
 
#include "CeresEngine/Foundation/Traits/is_movable.hpp"
#include "CeresEngine/Foundation/Traits/iter_difference.hpp"
 
#include <type_traits>
 
namespace CeresEngine::traits {
 
    template<class I, class = void> struct is_weakly_decrementable : std::false_type {};
 
    template<class I>
    struct is_weakly_decrementable<I,
        std::void_t<
            // clang-format off
            decltype(std::declval<I>()--),
            decltype(--std::declval<I>()),
            iter_difference_t<I>
            // clang-format on
            >>
            : std::conjunction<
                  // clang-format off
              is_movable<I>,
              std::is_same<decltype(--std::declval<I>()), I&>
                  // clang-format on
                  > {};
 
    template<class I> bool constexpr is_weakly_decrementable_v = is_weakly_decrementable<I>::value;
 
    template<class I>
    concept weakly_decrementable = is_weakly_decrementable_v<I>;
 
} // namespace CeresEngine::traits