I'm not really following this thread, so I might be missing important context, but I think it's possible the base class could be an abstract class, perhaps providing nothing except the ability for concrete subclasses to make singleton instances of themselves. You might reuse this class in different applications that need singletons. Or you might have multiple singleton classes within one application, all inheriting from the base class. Or within your app you might use one concrete class as a temporary placeholder for debugging, which would be replaced by the real class in production.
--Andy On Apr 17, 2011, at 2:11 AM, Dave DeLong wrote: > This is a truly strange question. If you interpret a singleton to be "one and > only one", then it doesnt make much sense to ask about subclassing it, > because that would imply that you could instantiate one of the base type and > one of the sub type, thus making it not fit the definition of a singleton. > > However, if we put philosophical discussions aside and simply ask for a > maximum of one instance per class, then I'd probably do something like this: > instead of using a single static variable to hold your singleton, use a > mutable dictionary instead. The keys of the dictionary would be the name of > the class, and the corresponding values would be e singleton objects. > Override +allocWithZone: to either return the appropriate and existing > object, or capture the call to super and save it in the dictionary before > returning it. Of course, this would preclude any of the subclasses doing > [self release] and returning a new object, but that's probably an adequate > compromise. > > Dave > > Sent from my iPad > > On Apr 16, 2011, at 10:20 PM, WT <jrca...@gmail.com> wrote: > >> how would you implement a *true* singleton class that supports subclassing? _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
