std::tuple and standard layout

Question

If all of the members of std::tuple are of standard layout types, is that std::tuple itself standard layout? The presence of a user-defined copy-constr

Answer 1

The "list" approach can be used to get standard layout tuple (the following example has some inaccuracies but demonstrates the idea):

template 
struct tuple;

template 
struct tuple {
    T value;
    tuple next;
};

template <>
struct tuple<> {};

namespace details {
    template 
    struct get_impl {
        template 
        constexpr static auto process(const tuple& t) {
            return get_impl::process(t.next);
        }
    };

    template <>
    struct get_impl<0> {
        template 
        constexpr static auto process(const tuple& t) {
            return t.value;
        }
    };
}

template 
constexpr auto get(const tuple& t) {
    return details::get_impl::process(t);
}

template 
constexpr auto make_tuple(Args&&... args) {
    return tuple{std::forward(args)...};
}