Mediator - shoonie/StudyingDesignPattern GitHub Wiki

Intent

Define an object that encapsulates how a set of objects interact. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently.

Diagram

disgram

Consequences

It limits subclassing.
It decouple colleagues.
It simplifies object protocols.
it abstracts how object cooperate.
It centralizes control.

Implementation

Omitting the abstract Mediator class.
Colleague-Mediator communication.

Sample Code

//https://en.wikibooks.org/wiki/C%2B%2B_Programming/Code/Design_Patterns/Behavioral_Patterns
class MediatorInterface;

class ColleagueInterface {
	std::string name;
public:
	ColleagueInterface(const std::string& newName) : name(newName) {}
	std::string getName() const { return name; }
	virtual void sendMessage(const MediatorInterface&, const std::string&) const = 0;
	virtual void receiveMessage(const ColleagueInterface*, const std::string&) const = 0;
};

class Colleague : public ColleagueInterface {
public:
	using ColleagueInterface::ColleagueInterface;
	virtual void sendMessage(const MediatorInterface&, const std::string&) const override;
private:
	virtual void receiveMessage(const ColleagueInterface*, const std::string&) const override;
};

class MediatorInterface {
private:
	std::list<ColleagueInterface*> colleagueList;
public:
	const std::list<ColleagueInterface*>& getColleagueList() const { return colleagueList; }
	virtual void distributeMessage(const ColleagueInterface*, const std::string&) const = 0;
	virtual void registerColleague(ColleagueInterface* colleague) { colleagueList.emplace_back(colleague); }
};

class Mediator : public MediatorInterface {
	virtual void distributeMessage(const ColleagueInterface*, const std::string&) const override;
};

void Colleague::sendMessage(const MediatorInterface& mediator, const std::string& message) const {
	mediator.distributeMessage(this, message);
}

void Colleague::receiveMessage(const ColleagueInterface* sender, const std::string& message) const {
	std::cout << getName() << " received the message from " << sender->getName() << ": " << message << std::endl;
}

void Mediator::distributeMessage(const ColleagueInterface* sender, const std::string& message) const {
	for (auto x : getColleagueList())
		if (x != sender)  // Do not send the message back to the sender
			x->receiveMessage(sender, message);
}

int main() {
	Colleague *bob = new Colleague("Bob"), *sam = new Colleague("Sam"), *frank = new Colleague("Frank"), *tom = new Colleague("Tom");
	Colleague* staff[] = { bob, sam, frank, tom };
	Mediator mediatorStaff, mediatorSamsBuddies;
	for (auto x : staff)
		mediatorStaff.registerColleague(x);
	bob->sendMessage(mediatorStaff, "I'm quitting this job!");
	mediatorSamsBuddies.registerColleague(frank);  
	mediatorSamsBuddies.registerColleague(tom);  // Sam's buddies only
	sam->sendMessage(mediatorSamsBuddies, "Hooray!  He's gone!  Let's go for a drink, guys!");
	return 0;
}