C++11中张量的递归索引

template <typename T, size_t N>
struct tensor {
    using type = std::array<typename tensor<T, N-1>::type, M>;
};

template <typename T>
struct tensor<T, 0> {
    using type = T;
};

template <typename T, size_t N, size_t M>
typename std::enable_if<(N > 0), typename tensor<T, N>::type&>::type
get_element(typename tensor<T, N>::type& t, size_t index, std::array<size_t, M>& indices) {
    return get_element<T, N-1, M>(t[index], indices);
}

template <typename T, size_t M>
typename std::enable_if<(M == 0), typename tensor<T, 0>::type&>::type
get_element(typename tensor<T, 0>::type& t, size_t index, std::array<size_t, M>& indices) {
    return t;
}

int main() {
    tensor<int, 3>::type t = {{{1, 2, 3}, {4, 5, 6}}, {{7, 8, 9}, {10, 11, 12}}};
    std::array<size_t, 3> indices = {0, 1, 2};
    int element = get_element<int, 3, 3>(t, 0, indices);
    std::cout << "Element: " << element << std::endl;
    return 0;
}