Program Listing for File KPSubject.hpp

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// References:
// https://embeddedartistry.com/blog/2017/02/01/improving-your-callback-game/
// https://en.cppreference.com/w/cpp/language/parameter_pack
#pragma once
#include <KPFoundation.hpp>
#include <functional>
#include <unordered_map>

template <typename T>
class KPSubject {
protected:
    using ObserverType = T;
    std::unordered_map<int, ObserverType *> observers;

public:
    int addObserver(ObserverType * o) {
        auto token = rand();
        while (!observers.insert({token, o}).second) {
            token = rand();
        }

        return token;
    }

    auto addObserver(ObserverType & o) -> decltype(addObserver(&o)) {
        return addObserver(&o);
    }

    void removeObserver(int token) {
        observers.erase(token);
    }

    template <typename F, typename... Types>
    void updateObservers(F method, Types &&... args) {
        for (auto & k : observers) {
            println("Updating ", k.second->ObserverName());
            (k.second->*method)(std::forward<Types>(args)...);
        }
    }
};