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What is the difference b/w NSArray and NSMutableArray?
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NSMutableArray and NSArray both are build on CFArray , performance/complexity should be same. The access time for a value in the array is guaranteed to be at worst O(lg N) for any implementation, current and future, but will often be O(1) (constant time).
NSArray creates static arrays, and NSMutableArray creates dynamic arrays. You can use arrays when you need an ordered collection of objects. NSArray is “toll-free bridged” with its Core Foundation counterpart, CFArrayRef . See Toll-Free Bridging for more information on toll-free bridging.
The main difference is that NSArray is for an ordered collection and NSSet is for an unordered collection. There are several articles out there that talk about the difference in speed between the two, like this one. If you're iterating through an unordered collection, NSSet is great.
The NSMutableArray class declares the programmatic interface to objects that manage a modifiable array of objects. This class adds insertion and deletion operations to the basic array-handling behavior inherited from NSArray .
NSMutableArray (and all other classes with Mutable in the name) can be modified. So, if you create a plain NSArray, you cannot change its contents later (without recreating it). But if you create an NSMutableArray, you can change it — you'll notice it has methods like -addObject: and -insertObject:atIndex:.
See the documentation for details.
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