template<typename... Ts>
  class SoA : public tuple<vector<Ts>...> {
          // ...
          template<size_t... Is>
          tuple<Ts&...> subscript(size_t i, index_sequence<Is...>) {
                  return {get<Is>(*this)[i]...};
          }
  public:
          // ...
          auto operator[](size_t i) {
                  return subscript(i, index_sequence_for<Ts...>{});
          }
  };