A clever compiler might be able to infer "structural typing", which is basically "duck typing" done at compile time. So, if you add a property "bar" to an objec

A clever compiler might be able to infer "structural typing", which is basically "duck typing" done at compile time. So, if you add a property "bar" to an object "foo", and you have some other code that calls "baz.bar", you can infer that "foo" is of type "HasABar", and "baz" is of type "HasABar", therefore it might be safe to use "foo" in place of "baz". The tricky part would be consolidating every structural subtype into cohesive classes.