Why would you ever want this kind of uncertainty in-process? If I have an object that lives in my process and I want to call a function on it, I rely on the compiler to tell whether that function exists or not. If it doesn't, why would I ship with code that will never work?

If we're talking remote calls, sure, there is never any guarantee that the recipient has that method, or that it's even listening anyway.

All of that to say that that whole discussion between function call or message passing is a waste of time and irrelevant in programming.