type
  TUnknownImplements = class(TObject, IUnknown)
  public
    function QueryInterface(const IID: TGUID; out Obj): HResult; stdcall;
    function _AddRef: Integer; stdcall;
    function _Release: Integer; stdcall;
  end;

  ISomeInterface = interface
    procedure DoSomething;
  end;

  TSomeClass = class(TObject, ISomeInterface)
  private
    function GetUnknown: TUnknownImplements;
    property Unknown: TUnknownImplements read GetUnknown implements ISomeInterface;
  protected
    procedure DoSomething;

  end;

{ TUnknownImplements }

function TUnknownImplements.QueryInterface(const IID: TGUID; out Obj): HResult;
begin
  Result := S_FALSE;
end;

function TUnknownImplements._AddRef: Integer;
begin
  Result := -1;
end;

function TUnknownImplements._Release: Integer;
begin
  Result := -1;
end;

{ TSomeClass }
procedure TSomeClass.DoSomething;
begin
   Writeln('ok');
end;

function TSomeClass.GetUnknown: TUnknownImplements;
begin
  Result := nil;
end;

procedure AniWork(v: ISomeInterface);
begin
  v.DoSomething();
end;

procedure TestProc;
var
  SC: TSomeClass;
begin
  SC := TSomeClass.Create;
  try
    AniWork(SC);
  finally
    SC.Free;
  end;
end;