type_reduce.hpp

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// -----------------------------------------------------------------------------------------------------
// Copyright (c) 2006-2021, Knut Reinert & Freie Universität Berlin
// Copyright (c) 2016-2021, 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 <seqan3/std/concepts>
#include <seqan3/std/ranges>
#include <seqan3/std/span>
#include <string_view>
 
#include <seqan3/core/detail/template_inspection.hpp>
#include <seqan3/core/range/detail/adaptor_base.hpp>
 
namespace seqan3::detail
{
 
// ============================================================================
//  type_reduce_fn (adaptor definition)
// ============================================================================
 
class type_reduce_fn : public adaptor_base<type_reduce_fn>
{
private:
    using base_t = adaptor_base<type_reduce_fn>;
 
public:
    using base_t::base_t;
 
private:
    friend base_t;
 
    template <std::ranges::range urng_t>
    static constexpr auto impl(urng_t && urange)
    {
        static_assert(std::ranges::viewable_range<urng_t>,
                      "The views::type_reduce adaptor can only be passed viewable_ranges, i.e. Views or &-to-non-View.");
 
        // views are always passed as-is
        if constexpr (std::ranges::view<std::remove_cvref_t<urng_t>>)
        {
            return std::views::all(std::forward<urng_t>(urange));
        }
        // string const &
        else if constexpr (is_type_specialisation_of_v<std::remove_cvref_t<urng_t>, std::basic_string> &&
                           std::is_const_v<std::remove_reference_t<urng_t>>)
        {
            return std::basic_string_view{std::ranges::data(urange), std::ranges::size(urange)};
        }
        // contiguous
        else if constexpr (std::ranges::borrowed_range<urng_t> &&
                           std::ranges::contiguous_range<urng_t> &&
                           std::ranges::sized_range<urng_t>)
        {
            return std::span{std::ranges::data(urange), std::ranges::size(urange)};
        }
        // random_access
        else if constexpr (std::ranges::borrowed_range<urng_t> &&
                           std::ranges::random_access_range<urng_t> &&
                           std::ranges::sized_range<urng_t>)
        {
            return std::ranges::subrange<std::ranges::iterator_t<urng_t>, std::ranges::iterator_t<urng_t>>
            {
                std::ranges::begin(urange),
                std::ranges::begin(urange) + std::ranges::size(urange),
                std::ranges::size(urange)
            };
        }
        // pass to std::views::all (will return ref-view)
        else
        {
            return std::views::all(std::forward<urng_t>(urange));
        }
    }
};
 
} // namespace seqan3::detail
 
// ============================================================================
//  views::type_reduce (adaptor instance definition)
// ============================================================================
 
namespace seqan3::views
{
inline constexpr auto type_reduce = detail::type_reduce_fn{};
 
} // namespace seqan3::views
 
namespace seqan3
{
template <typename t>
using type_reduce_t = decltype(views::type_reduce(std::declval<t>()));
}