type_reduce.hpp

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// -----------------------------------------------------------------------------------------------------
// Copyright (c) 2022 deCODE Genetics
// 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/biocpp/biocpp-core/blob/main/LICENSE.md
// -----------------------------------------------------------------------------------------------------
 
#pragma once
 
#include <concepts>
#include <ranges>
#include <span>
#include <string_view>
 
#include <bio/meta/type_traits/template_inspection.hpp>
#include <bio/ranges/concept.hpp>
#include <bio/ranges/views/detail.hpp>
 
namespace bio::ranges::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.");
 
        // string const &
        if constexpr (std::ranges::borrowed_range<urng_t> && std::ranges::contiguous_range<urng_t> &&
                      std::ranges::sized_range<urng_t> &&
                      std::same_as<std::ranges::range_reference_t<urng_t>, char const &>)
        {
            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 bio::ranges::detail
 
// ============================================================================
//  views::type_reduce (adaptor instance definition)
// ============================================================================
 
namespace bio::ranges::views
{
 
inline constexpr auto type_reduce = detail::type_reduce_fn{};
 
 
} // namespace bio::ranges::views
 
namespace bio::ranges
{
template <typename t>
using type_reduce_view = decltype(views::type_reduce(std::declval<t>()));
} // namespace bio::ranges