On Fri, Feb 12, 2010 at 12:07 AM, Charles Srstka <cocoa...@charlessoft.com> wrote: > On Feb 11, 2010, at 10:28 PM, Graham Cox wrote: > >> On 12/02/2010, at 1:43 PM, Gordon Apple wrote: >> >>> My point was that if all Cocoa classes called "init" >>> somewhere in their other initializers (or had a two-step initialization >>> similar to what MacApp did), then you could simply override (not call) >>> "init" for simple ivar initialization in a subclass, which would in no way >>> interfere with a designated initializer. >> >> >> Except that it would be all too easy to create an infinite loop. A subclass >> might implement -init to call super's designated initializer, which later >> calls -init. >> >> I'm not sure what's complex about overriding the designated initializer - >> even if it has a complex set of parameters, (and most do not) then all you >> do is pass them up to super. Your suggestion would only save a tiny, tiny >> amount of work yet lead to potentially big problems. >> >> --Graham > > Not really; suppose you want to subclass some class that has two separate > init methods: > > - (id)initWithFoo:(Foo *)foo; > - (id)initWithBar:(Bar *)bar; > > and suppose you just want to set some initial internal state, which needs to > always be set the same way at init time no matter how the object is > initialized. Which init method do you override? It’s possible that the > “initWithFoo:” method may look like this:
You override the one that's documented to be the designated initializer. > Incidentally, there is just such a class in Cocoa: NSDocument. It provides > six different init methods: > > - (id)init; > - (id)initForURL:(NSURL *)absoluteDocumentURL withContentsOfURL:(NSURL > *)absoluteDocumentContentsURLofType:(NSString *)typeName error:(NSError > **)outError; > - (id)initWithContentsOfURL:(NSURL *)absoluteURL ofType:(NSString *)typeName > error:(NSError **)outError; > - (id)initWithType:(NSString *)typeName error:(NSError **)outError; > - (id)initWithContentsOfFile:(NSString *)fileName ofType:(NSString *)docType; > - (id)initWithContentsOfURL:(NSURL *)aURL ofType:(NSString *)docType; > > Yes, the last two of these are deprecated, but it’s still possible that they > could get called, so you’d still have to take that into account. > Interestingly, though, someone at Apple appears to agree with Gordon here, > since all of those NSDocument initializers actually seem to call -[self init] > instead of -[super init], with the result that you can in fact just override > -init instead of having to override all six methods separately (and the > NSDocument subclass template even includes an -init method, to further > encourage this). They call -[self init] because NSDocument's designated initializer is -init. It's not a mystery, you just read the documentation and see which one is the designated initializer, then override that and call super. Mike _______________________________________________ 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
