Question

Consider this syntactically correct(?) pseudocode:

class Event {
public:
    virtual int getID() const = 0;
    virtual int getSize() = 0;
    virtual void* getData() = 0;
    virtual void setData() = 0;
    //(I cannot define data at this level 'cos I don't know what it is yet)
}

class SpecialEvent : class Event {
public:
    virtual int getPGNID() const = 0;
    int getSourceAddress() {return source_address;}
    int setSourceAddress(int source_address) {this->source_address = source_address;}
protected:
    int source_address;
}

template <typename T, typename E>
class EventWrapper : public E {
    T data;
public:
    static int EVENT_ID;
    //implements everything in Event...EVENT_ID is assigned at runtime by some registry
}

class AnEvent : public EventWrapper<int, Event> {
     //public methods specific to AnEvent...
}

class AnotherEvent : public EventWrapper<long, SpecialEvent> {
    int getPGNID() const {static int ID = 10; return ID;}
}

class TheProcessingClass {
    AnEvent event1;
    AnotherEvent event2;

    void process(Event& e);
    void process(SpecialEvent& e);

    void doSomething() {
        process(event1);  //should invoke process(Event&)
        process(event2);  //should invoke process(SpecialEvent&)
    }
}

Essentially, I have a wrapper class that wraps data of type T and inherits from some type of E (in this case Event or SpecialEvent)…

I initially was going to create two wrapper classes EventWrapper and SpecialEventWrapper until I figured out that both classes would have the exact same code in it (as long as it was extending from some type of Event)

First off, this sounds like a policy-based design. However, the Events don’t have any special behavior…they just hold some data… Am I abusing this pattern?

Second off, is there a better way to do this? I’m oversimplifying things greatly here, but any insights will be appreciated…

EDIT
I updated my example…in short, the processing classes are listening for Events and should take action based on the Event. I hope this helps…

Answer 1

I suggest adding process() as a member function of class event.

class Event {
    int getID() const;
    void process();
    //class stuff
}

class SpecialEvent : class Event {
    int getSpecialID() const;
    void process(); //special version of process()
    //class stuff
}


class TheProcessingClass {
    Event event1;
    SpecialEvent event2;

    void doSomething() {
        event1.process();
        event2.process();
    }
}