> On Aug 10, 2015, at 3:50 PM, Seth Willits <sli...@araelium.com> wrote: > > Say that I am taking this approach because it'd be impossible for a > YourSubclass instance to call initWithValue: on itself with an acceptable > "default" value; One is required by the client. > > Even though -init is unavailable, it's still actually possible to call > -convenienceInitializer, which will end up calling -[YourSubclass init] and > hitting the abort. That's bad. > > We can reason that by definition, convenienceInitializer must call > SomeSuperclass's designated initializer -init. Since we know that -init > cannot possibly setup a YourSubclass instance correctly, then we shouldn't > allow convenienceInitializer to be called either. So now we'd have to mark > convenienceInitializer as NS_UNAVAILABLE in YourSubclass's interface. > > By declaring: > > @interface YourSubclass > -(id) init NS_UNAVAILABLE; > -(id) convenienceInitializer NS_UNAVAILABLE; > @end > > … this now leaves us correctly unable to call [[YourSubclass alloc] init] or > [[YourSubclass alloc] convenienceInitializer]. > > Which brings me right back to my original question. If neither of those can > be called, then implementations of them in YourSubclass could never be > called. Right? If not, then why does YourSubclass need to provide > implementations?
Writing a halting cover for the superclass's designated initializers is a defensive measure. If you miss one of the convenience initializers then getting an immediate crash with a crash log pointing to the initializer is much better than quietly calling the wrong initializers and mysteriously crashing somewhere else later. The compiler's enforcement is for designated initializers because they should be a bottleneck that the compiler can see. Enforcing covers of every superclass convenience initializer would be difficult because it's likely that the compiler can't see them all when compiling your subclass, and would be cumbersome because there are often many more convenience initializers. -- Greg Parker gpar...@apple.com Runtime Wrangler _______________________________________________ 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: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
