[fpc-pascal]no refcounted interfaces

[Florian Klaempfl]

Dean Zobec wrote:

> I've talked with some friends of mine about the use of Interface base classes 
> without reference counting in Delphi 
> like this
> type
>   TNoRefCount = class(TObject, IUnknown)
>   protected
>     function QueryInterface(const IID:TGUID; out Obj):HResult; stdcall;
>     function _AddRef: Integer; stdcall;
>     function _Release: Integer; stdcall;
>   end;
>  
> function TNoRefCount.QueryInterface(const IID:TGUID; out Obj): HResult;
> begin
>   if GetInterface(IID, Obj) then
>     Result := 0
>   else
>     Result := Windows.E_NoInterface;
> end;
>  
> function TNoRefCount._AddRef: Integer;
> begin
>   Result := -1
> end;
>  
> function TNoRefCount._Release: Integer;
> begin
>   Result := -1
> end;
> 
>  
> We are all experiencing the same kind of problems:
> 
> 1) there's no easy way to obtain a TObject from an interface (whereas there's 
> no particular reason not to have it. A solution proposed was to implement an 
> AsObject method in  all the interfaces used.
> 2) there's no FreeAndNil function that would free the interface and the object 
> instance. 
> 
> It would be nice to be able to do something like this in an abstract factory:
> var
>   MyRef: ISomeInterface;
> begin
>   MyRef := SomeFactory.CreateObject as ISomeInterface;
>   try
>     ...use MyRef...
>   finally
>     MyRef.AsObject.Free;
>     MyRef := nil;
>   end;
> end;
> 
> Any Idea of a solution in free pascal?

 From the fpc wiki 
(http://www.freepascal.org/wiki/wiki.phtml?title=Language_related_articles)

Interface type selection: The commandline switch -SI and the directive 
$interfaces (possible values: corba and com) allow you to choose the 
type of interfaces which has no parent. Interfaces with parent inherit 
the style from their parent regardless of the currently selected 
interface type.

     * COM style interfaces work like Delphi interfaces: they inherit 
implicitly from IUnknown and they are reference counted.
     * CORBA style interfaces are neither ref. counted nor do they 
inherit from IUnknown.