Le 11 juin 08 à 09:01, John Engelhart a écrit :
On Jun 10, 2008, at 11:28 AM, Charles Srstka wrote:I think the problem is that if NSArray has +[NSArray array] returning an NSArray, then NSMutableArray has to return an NSArray also, since it can't have a different method signature for the same method. As a result, if you called +[NSMutableArray array], the compiler would think you were getting a regular, non-mutable NSArray, and you'd get a warning if you tried to do this, although the code would still work:No, each class is allowed to define different types for the same method:http://developer.apple.com/documentation/Cocoa/Conceptual/ObjectiveC/Articles/chapter_9_section_2.html#/ /apple_ref/doc/uid/TP30001163-CH16-TPXREF161This whole business about '(NSArray *) means NSArray AND any of it's subclasses' is the result of sloppy thinking and confusing 'able to' with 'as per spec'.If you declare a method prototype as '-(NSArray *)resultsArray', then you have explicitly communicated that a NSArray is going to be returned. Not a NSMutableArray. Not 'Jimmies groovy array with red pin stripes'. A NSArray. Period. A NSMutableArray != a NSArray. If you're going to be returning (or accepting) more than a single class, you use id, which clearly communicates your intentions.A return type of NSArray * means something very explicit. "But all you can expect is an object that behaves like a NSArray, so returning a subclass of NSArray, like NSMutableArray, is perfectly legal!" You're exactly right that all I can expect is an object that behave like a NSArray. /Exactly/ like a NSArray. Not sorta. Not almost. Exactly. Because that's what you explicitly stated. So when the returned array mutates, either because you were sloppy and returned the pointer to your objects internal state, or because during its travels something, somewhere sends it a mutation message inside a @try / @catch block, I'm going to file a bug because whatever it is you returned did not behave like a NSArray. An / immutable/ array.
You have to fill a bug againt the library that mutates the NSArray, not the one that create it. If a method expects an NSArray, it have to use it like an NSArray and not like an NSMutableArray.
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