I was wondering if the following is useful, probably not. Reserve a spot on the vtable, which is automatically set to NULL.
class AClass { __virtualspot void caption(string text); //no implementation __virtualspot string caption(); } class BClass:AClass { } BClass b = new BClass(); b.caption = "test"; //compiles 1. Would compile. But it would not run if the vtable spot has not been filled up by some API. 2. Can derive from the class/interface, without providing the implementation.