template<class T, size_t N>
struct tuple_size<array<T, N>> : integral_constant<size_t, N> { };
template<size_t I, class T, size_t N>
struct tuple_element<I, array<T, N>> {
using type = T;
};
template<size_t I, class T, size_t N>
constexpr T& get(array<T, N>& a) noexcept;
template<size_t I, class T, size_t N>
constexpr T&& get(array<T, N>&& a) noexcept;
template<size_t I, class T, size_t N>
constexpr const T& get(const array<T, N>& a) noexcept;
template<size_t I, class T, size_t N>
constexpr const T&& get(const array<T, N>&& a) noexcept;