On 27 Jan 2016 7:10 am, "Elie Morisse via Digitalmars-d" < [email protected]> wrote: > > On Tuesday, 26 January 2016 at 15:53:39 UTC, Manu wrote: >> >> So, you're saying that if you have an 'I' pointer, which may be implemented by a C++ class, it still needs to be able to cast to Object, and therefore fails? I wonder if a C++ class could somehow be promoted to a D class when being derived in D, by having an Object placed somewhere. > > > It helps that Object is a just a handful of virtual methods. > > > On Tuesday, 26 January 2016 at 16:25:35 UTC, Benjamin Thaut wrote: >> >> 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. > > > Calypso has "hybrid" D classes inheriting from C++, with this layout: > > - D vptr > - D monitor > { start of C++ class } > - C++ vptr > - C++ fields... > - might be other vptr and fields if the C++ class has more than one base > { end of C++ class } > - D fields... > > and when downcasted to the C++ base class the "this" pointer gets adjusted to point towards the start of the C++ class.
This is exactly what I had in mind. An alternative would be to place Object at the start of 'D fields', same fixup logic.
