manip-gallery.cpp

#include <functional>
#include <iostream>
using Manip = std::function<void(std::ostream&)>;
std::ostream& operator<<(std::ostream& os, Manip m) {
  m(os);
  return os;
}
template <typename T>
Manip paren(T&& x) {
  return [x = std::forward<T>(x)](std::ostream& os) {
    os << '(' << x << ')';
  };
}
template <typename S>
Manip join(S) {
  return [](std::ostream&){};
}
template <typename S, typename T>
Manip join(S, T&& t) {
  return [t = std::forward<T>(t)](std::ostream& os){
    os << t;
  };
}
template <typename S, typename T, typename U, typename... Args>
Manip join(S s, T&& t, U&& u, Args&&... args) {
  return [s = s, t = std::forward<T>(t),
          r = join(s, std::forward<U>(u), std::forward<Args>(args)...)]
      (std::ostream& os){
    os << t << s << r;
  };
}
template <typename... Args>
Manip tuple(Args&&... args) {
  return [t = join(", ", std::forward<Args>(args)...)](std::ostream& os){
    os << paren(t);
  };
}
int main() {
  std::cout << tuple() << std::endl;
  std::cout << tuple(0) << std::endl;
  std::cout << tuple(1.2, 3.4, 5.6, 7.8) << std::endl;
}