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
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