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Why would an instance of NSMutableArray be immutable?
Nope. This is due to the way CF bridging works — the magic class __NSCFArray (?) is bridged to CFArray and CFMutableArray. To support mutable arrays, that means __NSCFArray has to subclass NSMutableArray. So all bridged NSArrays subclass NSMutableArray, whether or not the instance is mutable.
There is no good test other than seeing if it throws an exception when you try to mutate it. :-p At some point in your code you improperly cast something to NSMutableArray when you didn’t actually have a guarantee it was mutable; you may need to do a code review to figure out where. (It can be hard to tell, since Obj-C lets you implicitly cast from ‘id’ to an explicit class. I sometimes grouse about C++ making me write these explicitly, but it does make it clearer where I’m doing the type-casts.) —Jens |
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James Walker
I was trying to add an object to an array and got an exception saying that I was trying to modify an immutable object. I set a breakpoint just before the addObject: line, and said to lldb
po [formatsOfSize isKindOfClass: [NSMutableArray class]] and the reply was '\x01'. So it should be mutable, no? Is there a better run-time test for mutability? If it's a clue, po [formatsOfSize class] produced __NSCFArray . |
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