***** D method override mechanisms borked ******

[xs0]

Just a slight correction :)

> xs0 told in D.announce that it's possible to extend the
> functionality of interfaces without any extra overhead at all (but it
> would require more from the optimization logic of the compiler).

It's possible to eliminate (time) overhead for calls on the same 
reference beyond the first (like in a loop or whatever). The first call 
of an interface method would still be about twice as expensive* as a 
"regular" virtual call (now it's just a few percent slower).

On the other hand, there'd be no need for implicit casting on function 
boundaries that is happening now (currently, if you pass/return a class 
reference to a function expecting an interface reference, an implicit 
(runtime) cast happens, which would no longer be necessary).


xs0

*) that's just the speed of the call sequence, obviously the function 
itself executes at "regular" speed, so the difference is not that large 
in practice