class TaskBase {
public:
	virtual void exec() = 0;
	virtual void finish() = 0;
	virtual bool isFinished() = 0;
};

template<class T>
class Task : public TaskBase {
private:
	std::function<T()> fn;
	std::function<void(T)> cb;
	T result;
	std::atomic<bool> finished;
public:
	Task(std::function<T()> fun, std::function<void(T)> callback = nullptr) : fn(fun), cb(callback) {}
	virtual void exec() {
		finished = false;
		result = fn();
		finished = true;
	}
	virtual bool isFinished() {
		return finished.load();
	}
	virtual void finish() {
		cb(result);
	}
};