Variadic template type list enumerating.

main.cpp

#include <iostream>
using namespace std;

template <typename... T>
struct counter;

template <>
struct counter<> {
	static constexpr size_t count() {
		return 0;
	}
};

template <typename Head, typename... Tail>
struct counter<Head, Tail...> {
	static constexpr size_t count() {
		return 1 + counter<Tail...>::count();
	}
};

template <typename... T>
constexpr size_t count() {
	return counter<T...>::count();
}

int main() {
	cout << count<int, bool, unsigned int, char>() << endl;
	return 0;
}