advance.hpp

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// SPDX-License-Identifier: BSL-1.0
// SPDX-FileCopyrightText: Copyright (C) 2020 Tobias Hienzsch
 
#ifndef TETL_ITERATOR_ADVANCE_HPP
#define TETL_ITERATOR_ADVANCE_HPP
 
#include <etl/_iterator/iterator_traits.hpp>
#include <etl/_iterator/tags.hpp>
#include <etl/_type_traits/is_base_of.hpp>
 
namespace etl {
 
/// Increments given iterator it by n elements.
///
/// If n is negative, the iterator is decremented. In this case,
/// InputIt must meet the requirements of LegacyBidirectionalIterator,
/// otherwise the behavior is undefined.
///
/// https://en.cppreference.com/w/cpp/iterator/advance
///
/// \ingroup iterator
template <typename It, typename Distance>
constexpr auto advance(It& it, Distance n) -> void
{
    using category = typename iterator_traits<It>::iterator_category;
    static_assert(is_base_of_v<input_iterator_tag, category>);
 
    auto dist = typename iterator_traits<It>::difference_type(n);
    if constexpr (is_base_of_v<random_access_iterator_tag, category>) {
        it += dist;
    } else {
        while (dist > 0) {
            --dist;
            ++it;
        }
        if constexpr (is_base_of_v<bidirectional_iterator_tag, category>) {
            while (dist < 0) {
                ++dist;
                --it;
            }
        }
    }
}
 
} // namespace etl
 
#endif // TETL_ITERATOR_ADVANCE_HPP