Comment by yawaramin

Well, there's the old Component Object Model and cousins ... under this model an object a encountering a new object b will, essentially, ask 'I need this service performed, can you perform it for me?' If b can perform the service, a makes use of it; if not, not.

Another technique that occurs to me is from type theory ... here, instead of objects we'll talk in terms of values and functions, which have types. So e.g. a function a encountering a new function b will examine b's type and thereby figure out if it can/should call it or not. E.g., b might be called toJson and have type (in Haskell notation) ToJson a => a -> Text, so the function a knows that if it can give toJson any value which has a ToJson typeclass instance, it'll get back a Text value, or in other words toJson is a JSON encoder function, and thus it may want to call it.