template <typename T, unsigned int N>
unsigned int size(T const (&)[N])
{
  return N;
}

template <int N>
struct Factorial {
    enum { value = N * Factorial<N - 1>::value };
};

template <>
struct Factorial<0> {
    enum { value = 1 };
};

// Factorial<4>::value == 24
// Factorial<0>::value == 1
const int x = Factorial<4>::value; // == 24
const int y = Factorial<0>::value; // == 1

template <typename T, unsigned int N>
void print_array(T const (&arr)[N])       // both T and N are deduced
{
    std::cout << "[";
    for (unsigned int i = 0; i != N; ++i)
    {
        if (i != 0) { std::cout << ", ";
        std::cout << arr[i];
    }
    std::cout << "]";
}

int main()
{
    double x[] = { 1.5, -7.125, 0, std::sin(0.5) };
    print_array(x);
}

template <int N>
struct A
{
    // Other fields.
    int data[N];
};