• Heinz <malagana15 yahoo.es> Jan 28 2008
• Christopher Wright <dhasenan gmail.com> Jan 28 2008
• "Jarrett Billingsley" <kb3ctd2 yahoo.com> Jan 28 2008

Heinz <malagana15 yahoo.es> writes:

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?

Christopher Wright <dhasenan gmail.com> writes:

Heinz wrote:
 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?


Typing's done at compile time, so you need the class definition at that 
point. You can use a base class or interface, but that's about it. 
Unless you make the code that uses the dll symbols into a dll, which 
might work.

"Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:

"Heinz" <malagana15 yahoo.es> wrote in message 
news:fnlkma$10e5$1 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 :\