Reenabling Ada by default

[Florian Weimer]

* Per Bothner:

> You might also look at the GCJ way of implementing Java interfaces.
> An object reference is a plain pointer, and there are not extra
> per-object "vobject" fields as in C++.  Instead we use a kind of
> double dispatch using initialization-time-computed indexin, which
> yields constant-time dispatch.

Can you provide a pointer to a short, high-level documentation of this
approach?

It's probably a standard implementation technique for OO languages,
but by just looking at the code, I've trouble understanding what's
going on.