23 General utilities library [utilities]

23.3 Compile-time integer sequences [intseq]

23.3.2 Class template integer_­sequence [intseq.intseq]

namespace std {
  template<class T, T... I> struct integer_sequence {
    using value_type = T;
    static constexpr size_t size() noexcept { return sizeof...(I); }
  };
}
T shall be an integer type.