[fpc-pascal] casting interfaces and objects

Marc Santhoff M.Santhoff at t-online.de
Mon May 19 13:01:20 CEST 2008

Am Montag, den 19.05.2008, 09:16 +0200 schrieb Graeme Geldenhuys:
> Marc Santhoff wrote:
> > Am Sonntag, den 18.05.2008, 23:41 +0200 schrieb Graeme Geldenhuys:
> >> 2008/5/18 Marc Santhoff <M.Santhoff at t-online.de>:
> >>> Since the compiler dod not warn about using the "as" operator I assume
> >>> it is safe? Like this:
> >>>
> >>> procedure TObservable.DeRegister( obsv: IObserver );
> >>> var
> >>>        i: integer;
> >>> begin
> >>>        if (fObservers.count<=0) then exit;
> >>>        for i:=0 to fObservers.count-1 do begin
> >>>                if ((fObservers[i] as IObserver)=obsv) then begin
> >>
> >> I'm not a big Interfaces expert, but as for as I know using 'as' like
> >> that with Interfaces actually translates to a QueryInterface() call
> >> internally, which is why it is allowed.  I vaguely remember as issue
> >> between CORBA and COM interfaces and the 'as' call, because CORBA
> >> interfaces do not have a QueryInterface() implementation. Well,
> >> something like that... :-)
> > 
> > Okay, so there are still some unknowns.
> CORBA interfaces do not include the following methods. These are only 
> relevant to COM interfaces.
> function QueryInterface(const iid: tguid; out obj): longint; stdcall;
> function _AddRef: longint; stdcall;
> function _Release: longint; stdcall;

I know from compiling and the pdf docs.

> Everybody I know uses COM interfaces, except for one developers - Martin 
> from MSEgui project.  FPC defaults to COM style interfaces as well.

I think that's a matter of the environment. I switched to CORBA too,
because I wanted to get up a testing application fast. ;)

But CORBA isn't that widely used, I think. Dunno what will happen on
Windows when using corba for interfaces inside one application only, but
I'm not sure if I can avoid using COM. At least driving some other apps
like Winword or OO.o might come into play, but no export.


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