utility/tuple/concept.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 <tuple>
#include <type_traits>
 
#include <seqan3/core/detail/template_inspection.hpp>
#include <seqan3/utility/tuple/pod_tuple.hpp>
#include <seqan3/utility/type_list/type_list.hpp>
#include <seqan3/utility/type_traits/basic.hpp>
 
namespace seqan3::detail
{

template <typename tuple_t>
concept tuple_size = requires (tuple_t v) {
    { std::tuple_size<tuple_t>::value } -> std::convertible_to<size_t>;
};

template <typename tuple_t>
concept tuple_get = requires (tuple_t & v, tuple_t const & v_c) {
    requires std::tuple_size_v<tuple_t> > 0;
 
    typename std::tuple_element<0, tuple_t>::type;
 
    { get<0>(v) } -> std::convertible_to<typename std::tuple_element<0, tuple_t>::type>;
    //     requires weakly_assignable_from<decltype(get<0>(v)), typename std::tuple_element<0, tuple_t>::type>;
    //TODO check that the previous returns something that can be assigned to
    // unfortunately std::assignable_from requires lvalue-reference, but we want to accept xvalues too (returned
    // proxies)
    { get<0>(v_c) } -> std::convertible_to<typename std::tuple_element<0, tuple_t>::type>;
    { get<0>(std::move(v)) } -> std::convertible_to<typename std::tuple_element<0, tuple_t>::type>;
    { get<0>(std::move(v_c)) } -> std::convertible_to<typename std::tuple_element<0, tuple_t>::type const &&>;
};

template <detail::tuple_size tuple_t>
struct tuple_type_list
{
protected:
    template <size_t... Is>
    static constexpr auto invoke_to_type_list(std::index_sequence<Is...>)
    {
        return type_list<std::tuple_element_t<Is, tuple_t>...>{};
    }
 
public:
    using type = decltype(invoke_to_type_list(std::make_index_sequence<std::tuple_size<tuple_t>::value>{}));
};

template <detail::tuple_size tuple_t>
using tuple_type_list_t = typename tuple_type_list<tuple_t>::type;

template <typename... elements_t>
inline constexpr auto all_elements_model_totally_ordered(seqan3::type_list<elements_t...>)
    -> std::bool_constant<(std::totally_ordered<elements_t> && ... && true)>;

template <typename tuple_t>
    requires requires () {
        { detail::all_elements_model_totally_ordered(tuple_type_list_t<tuple_t>{}) };
    }
static constexpr bool all_elements_model_totally_ordered_v =
    decltype(detail::all_elements_model_totally_ordered(tuple_type_list_t<tuple_t>{}))::value;
} // namespace seqan3::detail
 
namespace seqan3
{
 
// ----------------------------------------------------------------------------
// tuple_like
// ----------------------------------------------------------------------------

template <typename t>
concept tuple_like = detail::tuple_size<std::remove_reference_t<t>> && requires (t v) {
    typename detail::tuple_type_list<std::remove_cvref_t<t>>::type;
 
    // NOTE(rrahn): To check the full tuple_concept including the get interface and the std::totally_ordered
    //              we need to make some assumptions. In general these checks can only be executed if the tuple is not
    //              empty. Furthermore, the std::totally_ordered can only be checked if all elements in the
    //              tuple are strict_totally_ordered. This is done, by the fold expression in the second part.
    requires (std::tuple_size<std::remove_reference_t<t>>::value == 0)
                 || (detail::tuple_get<std::remove_cvref_t<t>>
                     && (!detail::all_elements_model_totally_ordered_v<std::remove_cvref_t<t>>
                         || std::totally_ordered<std::remove_cvref_t<t>>));
};

template <typename t>
concept pair_like = tuple_like<t> && std::tuple_size_v<std::remove_reference_t<t>> == 2;
 
} // namespace seqan3