That changes the type of self, though, from T to T?. So how would defaultFoo behave? For -> Void functions you could exit early if self is nil, but what if the method returns a value?
I would like to have a decent solution for this, as I have a similar problem. Also, there’s a related pitch about requiring an explicit self when passing methods to escaping closures. So there appears to be some demand for improvements in this part of the language.