Observer.cpp

Go to the documentation of this file.

#include <iostream>
#include <string>
#include <list>
 
//this will be used one day, I'm sure
class IObserver {
public:
    virtual ~IObserver() {}
    virtual void update(const std::string &messageFromSubject) = 0;
};
 
class ISubject {
public:
    virtual ~ISubject() {}
    virtual void attach(IObserver *observer) = 0;
    virtual void detach(IObserver *observer) = 0;
    virtual void notify() = 0;
};
 
class ConcreteSubject : public ISubject {
    std::list<IObserver *> observers;
    std::string message;
 
public:
    virtual ~ConcreteSubject() {}
 
    void attach(IObserver *observer) override {
        observers.push_back(observer);
    }
 
    void detach(IObserver *observer) override {
        observers.remove(observer);
    }
 
    void notify() override {
        for (IObserver *observer : observers) {
            observer->update(message);
        }
    }
 
    void createMessage(std::string message = "Empty") {
        this->message = message;
        notify();
    }
};
 
class ConcreteObserver : public IObserver {
    std::string messageFromSubject;
    ConcreteSubject &subject;
    static int static_number;
    int number;
 
public:
    ConcreteObserver(ConcreteSubject &subject) : subject(subject) {
        this->subject.attach(this);
        number = ++static_number;
    }
 
    virtual ~ConcreteObserver() {
        subject.detach(this);
    }
 
    void update(const std::string &messageFromSubject) override {
       this->messageFromSubject = messageFromSubject;
        printInfo();
    }
 
    void printInfo() {
        std::cout << "Observer " << number << ": a new message is available --> " << messageFromSubject << std::endl;
    }
};