Fun with extern(C++)

[Benjamin Thaut via Digitalmars-d]

On Tuesday, 26 January 2016 at 16:13:55 UTC, Manu wrote:
>
> Probably, but the layout of the vtable is defined by the 
> interface,
> and the interface type is always known, so I don't see why there
> should be any problem. Whether it's extern(C++) or extern(D), 
> the
> class populating the vtable with functions knows the layout.
> I think it all comes down to this conversion to Object thing. 
> If an
> interface must do that, then that's probably an issue without 
> jamming
> an Object instance in the class somewhere.

For a C++ class the first entry in the vtable is actually the 
first virtual function. (usually the destructor).

For a D class the first entry in the vtable is the classinfo. 
Thus the problem if you derive a D class from a extern(C++) base 
class. I don't see any way to actually fix this, adjusting the 
this pointer won't help. Once you derive a D class from a 
extern(C++) base class it is no longer a fully functional D 
class. For example monitor (e.g. synchronized methods) won't work.