dll class inheritance

[Jarrett Billingsley]

"Heinz" <malagana15 at yahoo.es> wrote in message 
news:fnlkma$10e5$1 at digitalmars.com...
> Have you ever tried to cast or inherit from a class that´s in a dll?
>
> At compile time you´ll always get symbol errors.
>
> I´m able to create instances from a class with an export function that 
> returns the class but,
> what can i do to make special uses of this class such as casts?

I think you'd basically have to export (in the DLL) the typeinfo for the 
class, and then in your app, emit references to them using extern(D) and 
such.

This is a terrible mess, and DLLs have far more issues than that -- getting 
a DLL to link to a symbol within the app that loads it is hackish and only 
useable in certain circumstances, and there are interactions with the GC 
that I don't think anyone really understands.  Basically DLLs are terrible 
for anything more than a simple C interface, and their issues only make 
themselves known with D since it's got a lot more complex interfaces than C 
does.

The equivalent things on *nix systems and Darwin/OSX (SOs and Dylibs) are 
far more powerful, and basically work like a compile-time linker but at 
runtime, making this a non-issue on those platforms.

To solve this, there is DDL, D Dynamic Libraries, a library that allows you 
to dynamically (manually) load and link the object files produced by DMD on 
Windows.  It's a little rough around the edges but does what it's supposed 
to.  Now, deriving from a class that's in a library, that's something I 
don't think it can do, only because that has to be resolved at compile time, 
something that DDL can't be a part of :\