Using template meta-programming as a functional language in C++11

template_magicks.cpp

#include <iostream>
using namespace std;

////
//  Pattern match on a list of types, recursively ask for the last one
template <typename Head, typename... Tail>
struct last {
  using type = typename last<Tail...>::type;
};


////
//  Base case typedefs the last type
template <typename T>
struct last<T> {
  using type = T;
};


////
//  Value typed parameter to calculate Fibonacci
template <int N>
struct fib {
  static const long long value = N * fib<N - 1>::value;
};


////
//  Base case returns 1
template <>
struct fib<0> {
  static const long long value = 1;
};


////
//  This for some reason needs a declaration of variadic 
//  type parameters, whereas the last didn't.
template <typename... Types> struct counter;


////
//  Pattern match on a list of types, count them recursively
template <typename Head, typename... Tail>
struct counter <Head, Tail...> {
  static const int value = 1 + counter<Tail...>::value;
};


////
//  Base case, 0 type parameters
template <>
struct counter <> {
  static const int value = 0;
};


int main(void){

  using t = last<int, double>::type;
  t pi = 3.14159;  // Chose double

  cout << "Pi is " << pi << endl;

  cout << "Fib(20) = " << fib<20>::value << endl;

  cout << "There are " << counter<int, float, double, char>::value << " types" << endl;

  return 0;
}