iter_difference.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/has_difference_type.hpp"
#include "CeresEngine/Foundation/Traits/has_iterator_traits_difference_type.hpp"
#include "CeresEngine/Foundation/Traits/is_subtractable.hpp"
#include "CeresEngine/Foundation/Traits/remove_cvref.hpp"
 
#include <iterator>
#include <type_traits>
 
namespace CeresEngine::traits {
 
    template<class T, class = void> struct iter_difference {};
 
    template<class T>
    struct iter_difference<T,
        std::enable_if_t<
            // clang-format off
            has_iterator_traits_difference_type_v<remove_cvref_t<T>>
            // clang-format on
            >> {
        using type = typename std::iterator_traits<remove_cvref_t<T>>::difference_type;
    };
 
    template<class T>
    struct iter_difference<T,
        std::enable_if_t<
            // clang-format off
            !has_iterator_traits_difference_type_v<remove_cvref_t<T>> &&
            std::is_pointer_v<T>
            // clang-format on
            >> {
        using type = std::ptrdiff_t;
    };
 
    template<class T>
    struct iter_difference<T,
        std::enable_if_t<
            // clang-format off
            !has_iterator_traits_difference_type_v<remove_cvref_t<T>> &&
            !std::is_pointer_v<T> &&
            std::is_const_v<T>
            // clang-format on
            >> {
        using type = typename iter_difference<std::remove_const_t<T>>::type;
    };
 
    template<class T>
    struct iter_difference<T,
        std::enable_if_t<
            // clang-format off
            !has_iterator_traits_difference_type_v<remove_cvref_t<T>> &&
            !std::is_pointer_v<T> &&
            !std::is_const_v<T> &&
            has_iterator_traits_difference_type_v<remove_cvref_t<T>>
            // clang-format on
            >> {
        using type = typename T::difference_type;
    };
 
    template<class T>
    struct iter_difference<T,
        std::enable_if_t<
            // clang-format off
            !has_iterator_traits_difference_type_v<remove_cvref_t<T>> &&
            !std::is_pointer_v<T> &&
            !std::is_const_v<T> &&
            !has_iterator_traits_difference_type_v<remove_cvref_t<T>> &&
            is_subtractable_v<remove_cvref_t<T>>
            // clang-format on
            >> {
        using type = std::make_signed_t<decltype(std::declval<T>() - std::declval<T>())>;
    };
 
    template<class T> using iter_difference_t = typename iter_difference<T>::type;
 
} // namespace CeresEngine::traits