#include <iostream>
#include <string>

class Printer
{
public:
	void print(const std::string & str) const
	{
		std::cout << str << std::endl;
	}
};

class Message
{
public:
	virtual ~Message() { }
	virtual void print(const class Mediator & mediator) const;
};

class Mediator
{
	const Printer & printer;
	const Message & message;
public:
	Mediator(const Printer & pr, const Message & msg) :
		printer(pr),
		message(msg) { }
	void print() const
	{
		message.print(*this);
	}
	void print(const std::string & str) const
	{
		printer.print(str);
	}
};

void Message::print(const Mediator & mediator) const
{
	mediator.print("Hello world!");
}

void hello_world(const Mediator & mediator)
{
	mediator.print();
}

int main()
{
	Printer printer;
	Message message;
	hello_world(Mediator(printer,message));
	return 0;
}