[fpc-pascal] Passing a CORBA interface as parameter

[Sven Barth]

Am 20.12.2019 um 16:17 schrieb Adriaan van Os:
>
> I would like to pass a CORBA interface-type as parameter and test for 
> equality, So, for example, I have
>
> {$mode objfpc}
> {$interfaces corba}
>
> type
>     IMyInterface = Interface
>
>         [  '{34aad6d0-5884-4143-97c2-b6e330305ae3}']
>
>         Function MyFunc : Integer;
>     end;
>
> Now I can pass IMyInterface to TObject.GetInterface as the first 
> parameter, which is of type TGuid in the declaration.
>
> However, if I use the same TGuid parameter type in my own procedure
>
>     procedure TestInterfaceParameter
>           ( const theInterface            : TGuid);
>         begin
>           if IsEqualGUID
>            ( theInterface, ITestInterface1)
>             then writeln
>                ( 'theInterface = ITestInterface1')
>         end;
>
> then I run into the problem that IMyInterface is accepted as actual 
> parameter of TestInterfaceParameter and of IsEqualGUID only if 
> IMyInterface inherits from IUnknown (which I certainly don't want, as 
> it is reference counted). Strangely, TObject.GetInterface does accept 
> IMyInterface as a parameter. So where is the difference ? Is there 
> some compiler magic involved in TObject.GetInterface ?

The important difference in this regard between COM and CORBA interfaces 
is that for CORBA interfaces the "guid" is a ShortString, not a TGUID. 
Thus the compiler allows to convert a CORBA interface to a ShortString. 
For TObject.GetInterface this works, because it has a overload for 
ShortString. ;) (this is document here: 
https://www.freepascal.org/docs-html/current/ref/refse47.html#x100-1220007.6 
)

Regards,
Sven