template.cc

#include <iostream>

template<int n, class T>
struct cons {
  static const int value = n;
};

struct nil{};

/* count */
template<class T>
struct cnt {};

template<>
struct cnt<nil> {
  static const int value = 0;
};

template<int n, class T>
struct cnt<cons<n, T> > {
  static const int value = 1 + cnt<T>::value;
};

/* sum */
template<class T>
struct sum {};

template<>
struct sum<nil> {
  static const int value = 0;
};

template<int n, class T>
struct sum<cons<n, T> > {
  static const int value = n + sum<T>::value;
};


int main() {
  typedef cons<10, cons<20, cons<30, nil> > > lst;
  std::cout << "cnt: " << cnt<lst>::value << std::endl;
  std::cout << "sum: " << sum<lst>::value << std::endl;
  return 0;
}