observables.h

namespace Pattern {
	template <typename... TArgs> class Observable;

	template <typename... TArgs> class Observer {
		virtual void notify(TArgs... args) = 0;
		friend class Observable<TArgs...>;

	public:
		virtual ~Observer() {}
	};

	template <typename... TArgs> class Observable {
		using TObserver = Observer<TArgs...>*;
		std::unordered_set<TObserver> _observers;

	protected:
		void notifyAll(TArgs... args) {
			for (auto o : _observers) { o->notify(args); }
		}

	public:
		void subscribe(TObserver o) { _observers.insert(o); }
		void unsubscribe(TObserver o) { _observers.erase(o); };
	};
}