tuple_like.h

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#pragma once
 
#include "di/meta/algorithm.h"
#include "di/meta/core.h"
#include "di/meta/vocab.h"
#include "di/util/as_const.h"
#include "di/util/forward.h"
#include "di/util/get.h"
#include "di/util/move.h"
#include "di/vocab/tuple/tuple_element.h"
#include "di/vocab/tuple/tuple_size.h"
 
namespace di::concepts {
namespace detail {
    template<typename T, typename Indices>
    struct TupleLikeHelper;
 
    template<typename T, types::size_t index>
    concept HasTupleElement = requires { typename meta::TupleElement<T, index>; };
 
    template<typename T, types::size_t index>
    concept HasTupleGet = requires(T tuple) {
        util::get<index>(tuple);
        util::get<index>(util::as_const(tuple));
        util::get<index>(util::move(tuple));
        util::get<index>(util::move(util::as_const(tuple)));
    };
    concept HasTupleGet = requires(T tuple) {…}
 
    template<typename T, types::size_t... indices>
    struct TupleLikeHelper<T, meta::ListV<indices...>> {
        constexpr static bool value = ((HasTupleElement<T, indices> && HasTupleGet<T, indices>) && ...);
    };
    struct TupleLikeHelper<T, meta::ListV<indices...>> {…};
}
 
// NOTE: The TupleSize must be less than 256 in this definition because clang has a maximum limit of 256 when expanding
// fold expressions. This can happen in reasonable scenarios because a fixed-size array is a tuple-like type.
template<typename T>
concept TupleLike =
    concepts::Tuple<T> || (requires {
        vocab::tuple_size(types::in_place_type<meta::RemoveCVRef<T>>);
    } && (meta::TupleSize<T> < 256) && detail::TupleLikeHelper<T, meta::MakeIndexSequence<meta::TupleSize<T>>>::value);
}