#include #include #include using namespace std; class IObserver { public: virtual ~IObserver() = default; virtual void UpdateFromSubject() = 0; }; class ISubject { public: virtual ~ISubject() = default; void AddObserver(shared_ptr& pObserver) { m_lstObservers.push_front(pObserver); } void RemoveObserver(shared_ptr& pObserver) { m_lstObservers.remove(pObserver);} void NotifyAll() { for (const auto& pObserver : m_lstObservers) pObserver->UpdateFromSubject(); } private: forward_list> m_lstObservers; }; class YoutubeChannel : public ISubject { public: YoutubeChannel(string name) : m_strName(name) {} private: string m_strName; }; class User : public IObserver { public: User(string name) : m_strName(name) {} void UpdateFromSubject() override { cout << "Hi from " << m_strName << "...! I got notification.\n"; } private: string m_strName; }; IObserver* GetUserInfoFromThirdPartyLibrary() { return new User("Third_Party"); } int main() { YoutubeChannel yt1("Learn Cpp"); shared_ptr user1 = make_shared("Ketan"); shared_ptr user2 = make_shared("A"); shared_ptr user3 = make_shared("B"); shared_ptr user4 = make_shared("C"); shared_ptr user5(GetUserInfoFromThirdPartyLibrary()); yt1.AddObserver(user1); yt1.AddObserver(user2); yt1.AddObserver(user3); yt1.AddObserver(user4); yt1.AddObserver(user5); yt1.NotifyAll(); cout << "\n\n"; yt1.RemoveObserver(user2); yt1.RemoveObserver(user3); yt1.NotifyAll(); return 0; }

Observer_Demo