[chowells]

The biggest problem with classes is that they conflate two different concepts in a way that limits reusability.

When you have classes, you have subclassing, and subclassing means two different things at the same time. First, subclasses are the subtyping operation. If you want type B to be a subtype of A, B must subclass A. Second, they provide code reuse via inheritance.

Each of those things is useful, but there's no reason to tie them together. In fact, modern best practices in OO say to favor interfaces and delegation over subclassing, and that's precisely because it separates those two concerns.

As far as I can tell, this is what the paper was getting at - separating delegation of implementation from subtyping. Since this is already what OO best practices suggest, why is it controversial?