If I'm not mistaken, multiple inheritance can cause the vtable to be at
a non-zero offset on all compilers (if the first base isn't polymorphic).

14.11.2024 16:42, Frederick Virchanza Gotham via Std-Proposals пишет:
> The C++ programming language is held back by the Microsoft compiler's
> implementation of VTables. Every other C++ compiler places the pointer
> to the VTable right at the beginning of the object, but the Microsoft
> compiler sometimes places it elsewhere. This has the following
> consequences:
>
> (1) Cannot use dynamic_cast on a void*
>
> Assuming that we have a void* pointer that points to a polymorphic
> object, we would be able to use dynamic_cast on it to perform a
> side-cast or down-cast (or to get the most-derived object).
>
> (2) Cannot get the type_info from a void*
>
> Assuming that we have a void* pointer that points to a polymorphic
> object, we would be able to get its type_info.
>
> I think the committee should consider giving Microsoft a certain
> amount of time to change this. I realise that the Standard doesn't
> mention 'Microsoft' in its text but the committee could make the
> decision that in C++36, the above two points are possible (which would
> mean that MS have to change their ABI by then).