I'm trying to write a generic observer pattern interface.

I'm trying to write a generic observer pattern interface.
I've found an old exemple on Delphi Praxis website. Looks interresting, Uwe Raabe wrote it : http://www.delphipraxis.net/1141754-post6.html

I took this code and tried to compile it under Delphi Berlin Update 2 :

INotifyObserver interface and TObserverSubject compile without any problem.

But Delphi cannot compile this

type
TMyClient = class(TInterfacedObject, INotifyObserver)
protected
procedure ObserverNotify(Sender: Integer);
end;

I'm getting E2065: Unsatisfied forward or external declaration: 'TMyclient.ObserverNotify'

Appears that compiler cannot handle the generic type ?
Any workaround ?
http://www.delphipraxis.net/1141754-post6.html