#include <boost/signal.hpp>
#include <iostream>

struct HelloWorld 
{
  void operator()() const 
  { 
    std::cout << "Hello, World!" << std::endl;
  } 
};

// ...
int main()
{
// Signal with no arguments and a void return value
	boost::signal<void ()> sig;

// Connect a HelloWorld slot
	HelloWorld hello;
	sig.connect(hello);

// Call all of the slots
	sig();
	
	return 0;
}