Functor in CPP

functor.cpp

template<typename R, typename ...Args>
class Functor {
protected:
    virtual R call(Args ...args) = 0;
public:
    R operator()(Args ...args) {
        return call(args...);
    }
};

class Foo : public Functor<int, int> {
    int n = 0;

    int call(int i) {
        n += i;
        return n;
    }
};


/*
// Example usage:

int main() {
    Foo foo;
    
    foo(1);
    foo(3);
    foo(1);

    int i = foo(0); // output: 5
}
*/