tuples.h

#ifndef UTILS_TUPLES_H
#define UTILS_TUPLES_H
 
#include <tuple>
 
namespace utils {
template <class... Ts, std::size_t... Is>
auto flatten_tuple_elements(std::tuple<Ts...>&& t, std::index_sequence<Is...>);
 
template <class T>
auto flatten_tuple(T&& t)
{
    return std::make_tuple(std::move(t));
}
 
template <class... Ts>
auto flatten_tuple(std::tuple<Ts...>&& t)
{
    constexpr std::size_t tuple_size =
        std::tuple_size<std::tuple<Ts...>>::value;
    return flatten_tuple_elements(
        std::move(t),
        std::make_index_sequence<tuple_size>());
}
 
template <class... Ts, std::size_t... Is>
auto flatten_tuple_elements(std::tuple<Ts...>&& t, std::index_sequence<Is...>)
{
    return std::tuple_cat(flatten_tuple(std::get<Is>(std::move(t)))...);
}
} // namespace utils
 
#endif