When using Class(y) it is possible (but neither correct or desirable) to create an object from a class that has one or more deferred methods. For example:
Function Main()
Local oFoo := Foo():new()
Return( NIL )
Create Class Foo
Export:
Message bar is deferred
End Class
Xbase++ correctly throws an error if you try and do the above. In my opinion this is a great improvement over Clipper/Class(y) but I mention it because it could be the cause of some "gotcha" errors.