std::apply

cppreference std::apply

Possible implementation

namespace detail
{
template<class F, class Tuple, std::size_t ... I>
constexpr decltype(auto) apply_impl(F &&f, Tuple &&t, std::index_sequence<I...>)
{
    // This implementation is valid since C++20 (via P1065R2)
    // In C++17, a constexpr counterpart of std::invoke is actually needed here
    return std::invoke(std::forward < F > (f), std::get<I>(std::forward<Tuple>(t))...);
}
}  // namespace detail

template<class F, class Tuple>
constexpr decltype(auto) apply(F &&f, Tuple &&t)
{
    return detail::apply_impl(std::forward < F > (f), std::forward < Tuple > (t), std::make_index_sequence<std::tuple_size_v<std::remove_reference_t<Tuple>>> { });
}