elements.hpp

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// -----------------------------------------------------------------------------------------------------
// Copyright (c) 2006-2022, Knut Reinert & Freie Universität Berlin
// Copyright (c) 2016-2022, 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 <ranges>
 
#include <seqan3/utility/tuple/concept.hpp>
#include <seqan3/utility/type_traits/basic.hpp>
 
namespace seqan3::views
{
template <auto index>
inline constexpr auto elements = std::views::transform(
    [](auto && in) -> decltype(auto)
    {
        using std::get;
        using seqan3::get;
 
        using element_t = decltype(in);
 
        static_assert(tuple_like<element_t>,
                      "You may only pass ranges to views::element_t whose reference_t models tuple_like.");
 
        // we need to explicitly remove && around temporaries to return values as values (and not as rvalue references)
        // we cannot simply cast to std::tuple_element_t (or set that as return value), because some tuples, like
        // our alphabet_tuple_base alphabets do not return that type when get is called on them (they return a proxy)
        using ret_type = remove_rvalue_reference_t<decltype(get<index>(std::forward<element_t>(in)))>;
        return static_cast<ret_type>(get<index>(std::forward<element_t>(in)));
    });
 
} // namespace seqan3::views