Am Sonntag, den 18.05.2008, 17:54 -0300 schrieb Joao Morais: > Marc Santhoff wrote: > > Hi, > > > > I have two questions about interface usage. > > > > 1. How interfaces are to handle when casting? > > Theoretically it should be safe to do this: > > > > TObservable = class > > public > > procedure Register( obsv: IObserver ); > > private > > procedure NotifyObservers(param: TParameter); > > fObservers: TFPObjectList; > > end; > > > > procedure TObservable.Register( obsv: IObserver ); > > begin > > fObservers.add(TObject(obsv)); > > end; > > It is safe to store, it isn't safe to use as an object -- you will need > to cast back to IObserver to use the instance.
As always. > > When using a cast from an interface to an object the compiler warns > > about the class types "TObject" and "IObserver" not being related. > > > > Since an implementor of in interface always will be a class type and any > > class type at least inherits from TObject, I assume it is okay? > > No no, they are quite different. So that's why the compiler issues a warning. > > Is there a better method of handling this case? > > Use TInterfaceList or IInterfaceList. That's nice, I only didn't know it until now. > > 2. Will an interface and a class with the same signature but not > > explicitely implementing this interface be runtime-compatible and > > interchangably usable? > > No. You need to include the interface in the class declaration or make a > workaround in the QueryInterface method. Which is a pretty clear solution, it's only important to give the programmer the opportunity to derive from a class or implement the interface himself. Many thanks, Marc _______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
