Question

After importing into delphi the com dll file, the delphi in turn generated a lib_tlb.pas file.

Inspecting the file it shows

Iinterface1 = interface(IDispatch)
    function func: Integer; safecall;
    procedure proc(param:Iinterface1);
end;

Cointerface1 = class
  class function Create: Iinterface;
  class function CreateRemote(const MachineName: string): Iinterface1;
end;

Tinterface1 = class(TOleServer)
    function func: Integer;
    procedure proc(param:Iinterface1);
end;

Now its clear to see that there is no connection between Tinterface1 and Iinterface1.

The problem comes when one calls proc with an Tinterface1. this will not compile Tinterface1 does not inheritce Iinterface1.

So what suggested to do? change the lib that is auto generated? or do you have a better idea of what to do when wanting to pass Tinterface1 to proc.

The example is a simplification of the code, in the code there is anther object that needs to be the one to be passed to proc, however that proc knows only its interface, which is the same problem.

update: as it seems the manual of the com dll file, says that proc should be

    procedure proc(param:^Tinterface1);

where the interface is only in delphi point of view.

Answer 1

TInterface1.Proc() is expecting a pre-existing IInterface1 object to be passed to it as input. Use Cointerface1.Create() to create that object, eg:

var
  intf: Iinterface1;
begin
  intf := Cointerface1.Create;
  TheOleServerInstance.proc(intf);
end;

Tinterface1 is a TOleServer descendant that does not directly inherit from Iinterface1 (but it does wrap an Iinterface1 internally), so you have to cast it whenever you want to pass it where an Iinterface1 is expected, eg:

var
  intf: Iinterface1;
  svr: Iinterface1;
begin
  intf := Cointerface1.Create;
  if Supports(TheOleServerInstance, Iinterface1, svr) then
    intf.proc(svr);
end;