Observer Pattern - C++

Observer.cpp

// Source: C++ Game Development Primer - Chapter 2
#include <vector>
#include <algorithm>
#include <iostream>


/*
 *  Step 1: Generic Observer Pattern
 */
template <typename Observer>
class Notifier {

    using Observers = std::vector<Observer*>;
    Observers m_observers;

public:
    void Add(Observer *newObserver)
    {
        assert(std::find(m_observers.begin(), m_observers.end(), newObserver)==m_observers.end());
        m_observers.emplace_back(newObserver);
        std::cout << "Adding a new observer...\n";
    }

    void Remove(Observer *toBeRemovedObserver)
    {
        auto found = std::find(m_observers.begin(), m_observers.end(), toBeRemovedObserver);
        if(found!= m_observers.end()) {
            m_observers.erase(found);
            std::cout << "Removing an observer...\n";
        }
    }

    template<void (Observer::*Method)()>
    void Notify()
    {
        for(auto o: m_observers)
            (o->*Method)();
    }
};





class QuitObserver {
public:
    virtual void OnQuit() = 0;
};


/*
 *     Step 2: Concrete Notifier (some class should be used <here> as its Observer type)
 */
class QuitButton: public Notifier<QuitObserver> {
public:
    void pressed()
    {
        Notify<&QuitObserver::OnQuit>();
    }
};


/*
 *      Step 3: Some class should implement Observer and subscribe to Notifier
 */
class Game : public QuitObserver {
    using QuitButtonPointer =  std::shared_ptr<QuitButton>;
    QuitButtonPointer m_quitButton { new QuitButton};

    void OnQuit() override
    {
        std::cout<<"Quiting game ...\n";
    }

public:
    Game(){
        m_quitButton.get()->Add(this);
        m_quitButton->pressed();
    }
    virtual ~Game(){m_quitButton.get()->Remove(this);}

};



int main()
{
    auto g = Game();
    return 0;
}