#include <iostream>
#include <type_traits>

// 2. the second template argument is only valid if T is an integral type:
template < class T,
           class = typename std::enable_if<std::is_integral<T>::value>::type>
bool is_even (T i) {return !bool(i%2);}

int main() {
  short int i = 1;    // code does not compile if type of i is not integral
  std::cout << std::boolalpha;
  std::cout << "i is even: " << is_even(i) << std::endl;

  return 0;
}