On Jul 13, 2009, at 08:49, I. Savant wrote:
Subclassing is fraught with many angry, fire-breathing, treasure- grubbing dragons and as such is *not* recommended.
On Jul 13, 2009, at 08:51, David W. Berry wrote:
NSMutableArray (and most/all of the collection classes) is an abstract class that can't be usefully sub-classed. The object returned by [NSMutableArray array] is actually a subclass of NSMutableArray.
As someone who's been guilty of making statements like these in the past, I just want to say : it ain't so. Subclassing NSArray is pretty easy (there are 5 primitive methods to override and you're done). What you *don't* get for free from subclassing is an internal storage mechanism -- you have to invent that for yourself (usually by putting a real NSArray instance variable in your subclass :) ). You also need a pretty clear understanding of how class clusters work, and that's where confusion can set in. The OP didn't have a clear understanding, and that led to his problem.
For the record, too, [NSMutableArray array] will normally return an object of the same concrete class as [NSArray array]. In Apple's implementation, they're the same thing, with the mutability enforced at run time. That's an implementation detail, of course, but it's worthwhile being aware of it.
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