Manipulator in C++11 era

manipulator.cpp

#include <functional>
#include <iostream>

class Manipulator {
 public:
  using FuncType = std::function<void(std::ostream&)>;
  Manipulator(const FuncType& f) : f_(f) {}
  void exec(std::ostream& os) const { f_(os); }
 private:
  FuncType f_;
};

std::ostream& operator<<(std::ostream& os, const Manipulator& m) {
  m.exec(os);
  return os;
}