Like boost signal implement with c++11

signal.hpp

#ifndef SIGNAL_HPP_INCLUDE
#define SIGNAL_HPP_INCLUDE

#include <functional>


template<typename Signature>
class Signal {
public:
  typedef typename std::function<Signature> Function;
  typedef typename Function::result_type Result;

  Signal(void);
  Signal(const Signal &);
  Signal &operator=(const Signal &);
  void connect(Function);

  template<typename... Args>
  Result operator()(Args&&... args);

private:
  Function f;
};

#include "signal_priv.hpp"

#endif /* end of include guard: SIGNAL_HPP_INCLUDE */

singal_priv.hpp

#ifndef SIGNAL_PRIV_HPP_INCLUDE
#define SIGNAL_PRIV_HPP_INCLUDE

template<typename Signature>
Signal<Signature>::Signal() {
}

template<typename Signature>
Signal<Signature>::Signal(const Signal &oth) {
  f = oth.f;
}

template<typename Signature>
Signal<Signature> &Signal<Signature>::operator=(const Signal &oth) {
  f = oth.f;
  return *this;
}


template<typename Signature>
void Signal<Signature>::connect(Function func) {
  this->f = func;
}

template<typename Signature>
template<typename... Args>
typename Signal<Signature>::Result
Signal<Signature>::operator()(Args&&... args) {
  return f(std::forward<Args>(args)...);
}


#endif /* end of include guard: SIGNAL_PRIV_HPP_INCLUDE */

I add a specialization for void(void) because if args is void it will cause error.
But it's a bad solution.