On Feb 17, 2012, at 8:51 PM, Ken Thomases wrote: > On Feb 17, 2012, at 2:33 PM, Ben Kennedy wrote: > >> On 16 Feb 2012, at 3:54 pm, Ken Thomases wrote: >> >>> In other words, you're being silly. It's clear to everyone that -[NSString >>> isEqual:] must have semantics built on -[NSString isEqualToString:], which >>> is clearly documented. >> >> What value does NSString's isEqualToString: bring to the table over its >> implementation of isEqual? Is it just a matter of foregoing an 'if ([obj >> isKindOfClass:[NSString class])' construct at the front end? Put another >> way, why does NSString provide isEqualToString: as a distinct method? > > The -[NSString isEqualToString:] docs say, "When you know both objects are > strings, this method is a faster way to check equality than isEqual:." > > In truth, though, the difference is probably slight. -isEqual: checks if the > other object pointer is nil, checks the class, and invokes -isEqualToString:. > So, there's a savings, but it's pretty trivial. Back in the day, though, > when CPUs were slower and the Objective-C runtime was less well optimized, it > might have been significant. At this point, of course, it has to be > maintained for backward compatibility. > > There's a minor type-safety advantage, too, I suppose. If you pass a pointer > whose static type is not NSString* or a subclass to -isEqualToString:, the > compiler will complain, possibly alerting you to a mistake. Similarly, when > implementing a -isEqualTo<Type>: method in one of your own classes, the type > of the argument will be the specific type instead of "id", so you can get > better checking of your implementation. > > Regards, > Ken
There is also arguably some value in the explicit declaration of intent when using the class-specific equality methods; e.g., that a given bit of code expects something to be a string. Preston _______________________________________________ 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
