Observer example

observer.cpp

#include <iostream>
#include <vector>
#include <map>
#include <functional>

using namespace std;

using observer = function<void()>;

enum class Events {A, B, C};

template<typename Event>
class Observer {
    public:
    void registerObs(Event e, observer obs) {
        observers[e].push_back(obs);
    };
    void notify(Event e) {
        for(auto obs: observers.at(e)) {
            obs();
        }
    };
    private:
        map<Event, vector<observer>> observers;
};

int main() {
    Observer<Events> o;
    
    o.registerObs(Events::A, bind([](string s){ cout << s << endl; }, "A1"));
    o.registerObs(Events::A, bind([](string s){ cout << s << endl; }, "A2"));
    o.registerObs(Events::B, bind([](string s){ cout << s << endl; }, "B1"));
    
    o.notify(Events::A);
    o.notify(Events::B);
}