slice.hpp

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// SPDX-FileCopyrightText: 2006-2025 Knut Reinert & Freie Universität Berlin
// SPDX-FileCopyrightText: 2016-2025 Knut Reinert & MPI für molekulare Genetik
// SPDX-License-Identifier: BSD-3-Clause

 
#pragma once
 
#include <concepts>
#include <iterator>
#include <ranges>
#include <span>
#include <stdexcept>
#include <type_traits>
 
#include <seqan3/core/range/detail/adaptor_from_functor.hpp>
#include <seqan3/io/exception.hpp>
#include <seqan3/utility/views/type_reduce.hpp>
 
namespace seqan3::detail
{
 
// ============================================================================
//  slice_fn (adaptor definition)
// ============================================================================

struct slice_fn
{
    constexpr auto operator()(ptrdiff_t begin_pos, ptrdiff_t end_pos) const noexcept
    {
        return detail::adaptor_from_functor{*this, begin_pos, end_pos};
    }

    template <std::ranges::viewable_range urng_t>
    constexpr auto operator()(urng_t && urange,
                              std::ranges::range_difference_t<urng_t> begin_pos,
                              std::ranges::range_difference_t<urng_t> end_pos) const
    {
        using position_t = std::ranges::range_difference_t<urng_t>;
        if constexpr (std::ranges::sized_range<urng_t>)
        {
            position_t urange_size = static_cast<position_t>(std::ranges::size(urange));
 
            begin_pos = std::min(begin_pos, urange_size);
            end_pos = std::min(end_pos, urange_size);
        }
        position_t target_size = end_pos - begin_pos;
 
        if (end_pos < begin_pos)
            throw std::invalid_argument{"end_pos argument to seqan3::views::slice must be >= the begin_pos argument."};
 
        // urange | type_reduce | drop | take
        return std::views::take(std::views::drop(seqan3::views::type_reduce(std::forward<urng_t>(urange)), begin_pos),
                                target_size);
    }
};
 
} // namespace seqan3::detail
 
// ============================================================================
//  views::slice (adaptor instance definition)
// ============================================================================
 
namespace seqan3::views
{
inline constexpr auto slice = detail::slice_fn{};
 
} // namespace seqan3::views