I would expect some comments on covariance here. With this you seem to have a magic first parameter x that gets to be dispatched based on the runtime type of x

I would expect some comments on covariance here. With this you seem to have a magic first parameter x that gets to be dispatched based on the runtime type of x, while y isn't and gets to be overloaded according to its static type. The dot notation at least conveys some notion of x being looked at in a different way than y.