On Fri, 2004-04-23 at 21:44, Jonathan Lang wrote: > OK: I'm planning on creating a widget which must not make use of any of > the indicator functionality of the HList; I don't just want to not use the > functionality - I want to have its use forbidden (letting the optimizer go > ahead and toss out the indicator role). So I'd like to create a subtype > of HList which exceises that functionality.
I think you're thinking of this backwards. Don't subclass HList. Create a new class that doesn't subclass anything and compose the appropriate roles into it. Provided the library designers have done their job and *ask for the proper role in function and method signatures, not a specific class*, you're groovy. Now I could be wrong about your intent, but the question "How do I subclass a class to *remove* functionality?" is the kind of "Yeah, it hurts when you do that" situation role-based composition try to avoid. If you have all of the pieces, put them together in a way you find most pleasing. -- c
