Problem with basic usage of std::enable_if

Question

I\'m trying to make a simple template function that given some parameters, it outputs them with a space in between. Some of those can be elements of an enum, and in that case I

Answer 1

Default template arguments are not part of the function definition. Use a dummy parameter instead, so that the second argument has a different type:

template<typename T, typename std::enable_if_t<std::is_enum<T>::value, int> = 0>
constexpr std::ostream& debug(const T& a) {
  std::cerr << (int)(a);
  return std::cerr;
}

template<typename T, typename std::enable_if_t<!std::is_enum<T>::value, int> = 0>
constexpr std::ostream& debug(const T& a) {
  std::cerr << a;
  return std::cerr;
}