Structs implementing interfaces in D1

[BCS]

Hello Tom,

> The concept is pretty simple. The mixin creates a vtable which points
> to
> a set of generated functions of the form { adjust the 'this' ptr; jump
> to the real function; }. Finally, the "InterfaceName
> asInterfaceName()"
> functions generated inside the struct return pointers to the
> corresponding vtables.

where is the vtable pointer placed?