Should this always work?

[frame]

On Saturday, 1 May 2021 at 15:52:52 UTC, Mike Parker wrote:

> No instance is being created by the cast. The instance already 
> exists. The cast just allows you to treat the pointer to the 
> instance as a specific type. It’s no different than casting 
> from C to A really. You just have the void* as an intermediary.

Yes, I know. In fact, this was a stupid question. Not sure what I 
was thinking off. I sometimes mix up languages in my head and 
came to weird conclusions :P



On Saturday, 1 May 2021 at 16:06:05 UTC, Steven Schveighoffer 
wrote:

> An interface cast involves a thunk (constant pointer 
> adjustment) to get to the interface/object. The reason is 
> because a class with interfaces stores interface vtable 
> pointers inside the object, and your interface reference points 
> at that. You can see when you cast between Object (concrete) 
> type and Interface type, the pointer value changes.
>
> So this will not work. It *does* work for base classes, because 
> the class vtable pointer is stored at same point, and casting 
> around class references does not involve a thunk.

This was helpful to understand the ABI chapter better.

Thanks, guys!