distance.hpp

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// SPDX-License-Identifier: BSL-1.0
// SPDX-FileCopyrightText: Copyright (C) 2019 Tobias Hienzsch
 
#ifndef TETL_ITERATOR_DISTANCE_HPP
#define TETL_ITERATOR_DISTANCE_HPP
 
#include <etl/_iterator/iterator_traits.hpp>
#include <etl/_iterator/tags.hpp>
#include <etl/_type_traits/is_base_of.hpp>
 
namespace etl {
 
/// \brief Returns the number of hops from first to last.
/// \details https://en.cppreference.com/w/cpp/iterator/distance
/// \ingroup iterator
template <typename It>
constexpr auto distance(It first, It last) -> typename iterator_traits<It>::difference_type
{
    using category = typename iterator_traits<It>::iterator_category;
    static_assert(is_base_of_v<input_iterator_tag, category>);
 
    if constexpr (is_base_of_v<random_access_iterator_tag, category>) {
        return last - first;
    } else {
        auto result = typename iterator_traits<It>::difference_type{};
        while (first != last) {
            ++first;
            ++result;
        }
        return result;
    }
}
 
} // namespace etl
 
#endif // TETL_ITERATOR_DISTANCE_HPP