#include <iostream>
using namespace std;
template<int base, int x>
struct Power {
static constexpr int a = base * (Power<base, x - 1>::a);
};
template<int base>
struct Power<base, 0> {
static constexpr int a = 1;
};
///////////////////////////////// I failed in creating a variable-template here.
template<int base, int x>
using power_v = typename Power<base, x>::a;
/////////////////////////////////
int main()
{
constexpr int y = power_v<3, 2>;
cout << y;
}
using is used for declaring type alias.
Type alias is a name that refers to a previously defined type (similar to typedef).
Alias template is a name that refers to a family of types.
As variable_template it should be
template<int base, int x>
constexpr int power_v = Power<base, x>::a;