[yndoendo]

Inheritance is not needed when a composite pattern can be used.

class DefaultTask { }

class SpecialTask { }

class UsedItem {

    UsedItem() { _task = new SpecialTask() }
    
    void DoIt() { _task.DoIt() }

}

Is python a OOP language? Self / this / object pointer has to be passed similar to using C style object-oriented / data abstraction.

[1718627440]

The interesting thing is, that in the OOP implementation inheritance IS composition of vtables and data. It's really only syntactic sugar, that is sometimes not unambiguous.

[zozbot234]

This is not quite correct. OOP implementation inheritance involves a kind of "open recursion" (that is, calls to base-class methods can end up dispatching to implementations from a derived class) that is not replicated with pure composition. All method calls, including method calls that originate from code in some class anywhere in the hierarchy, ultimately dispatch through the vtable of whatever object they're called on.

[1718627440]

But that's exactly the same you would need to implement manually when you use composition. When constructing, you also need to construct the contained objects, when doing something that should affect a contained object, you need to dispatch it.

When a method is never overridden, it doesn't need to be in the vtable.

[zozbot234]

That's not what people usually mean by "composition" though. The whole point of "use composition over inheritance" is to avoid that behavior.

[1718627440]

I don't see how you can use composition without eventually calling methods of the contained objects. Every method of the outer object either uses an inner object or it doesn't. Yes, using the inner object doesn't always means just delegating to a single call. You maybe would implement the outer by calling an inner objects method multiple times or different methods, but nothing stops you of doing the same thing with a super class. When you don't call to an inner object, it's the same as you adding another method to the subclass, without it being present in the parent class.

I think composition over inheritance is only about being explicit. That's it.

[maleldil]

Python doesn't require self to be passed. You need it in method definitions, but not calls.

[1718627440]

But you can do it. Actually you can call instance methods of other classes and change the class of an instance in Python like in C, but this dynamism is probably what makes it slow. Also doing that will make the program quite complicated, more so than in C, since Python also abstracts about this.