Final by default?

[Andrej Mitrovic]

On 3/13/14, Dmitry Olshansky <dmitry.olsh at gmail.com> wrote:
> This:
>
> final class A {
>      int i;
>      void f() { ++i; }
>      void g() { ++i; }
>
> }
> pragma(msg, __traits(isFinalFunction, A.g));
> pragma(msg, __traits(isFinalFunction, A.f));

Speaking of final classes, I've ran into this snippet a few weeks ago
in src/gc/gc.d:

-----
// This just makes Mutex final to de-virtualize member function calls.
final class GCMutex : Mutex {}
-----

But does this actually happen?