slice.hpp

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// -----------------------------------------------------------------------------------------------------
// Copyright (c) 2006-2020, Knut Reinert & Freie Universität Berlin
// Copyright (c) 2016-2020, Knut Reinert & MPI für molekulare Genetik
// This file may be used, modified and/or redistributed under the terms of the 3-clause BSD-License
// shipped with this file and also available at: https://github.com/seqan/seqan3/blob/master/LICENSE.md
// -----------------------------------------------------------------------------------------------------
 
#pragma once
 
#include <stdexcept>
 
#include <seqan3/io/exception.hpp>
#include <seqan3/range/concept.hpp>
#include <seqan3/range/views/detail.hpp>
#include <seqan3/range/views/drop.hpp>
#include <seqan3/range/views/take.hpp>
#include <seqan3/std/concepts>
#include <seqan3/std/iterator>
#include <seqan3/std/ranges>
#include <seqan3/std/span>
#include <seqan3/std/type_traits>
 
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
    {
        if constexpr (std::ranges::sized_range<urng_t>)
        {
            using position_t = std::ranges::range_difference_t<urng_t>;
            begin_pos = std::min(begin_pos, static_cast<position_t>(std::ranges::size(urange)));
            end_pos = std::min(end_pos, static_cast<position_t>(std::ranges::size(urange)));
        }
 
        if (end_pos < begin_pos)
            throw std::invalid_argument{"end_pos argument to seqan3::views::slice must be >= the begin_pos argument."};
 
        // urange | drop | take
        return views::take(views::drop(std::forward<urng_t>(urange), begin_pos), end_pos - begin_pos);
    }
 
    // does not require special overloads, because views::drop and views::take handle the flattening.
};
 
} // namespace seqan3::detail
 
// ============================================================================
//  views::slice (adaptor instance definition)
// ============================================================================
 
namespace seqan3::views
{
 
inline constexpr auto slice = detail::slice_fn{};
 
 
} // namespace seqan3::views