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    <p><code>copy</code> and <code>mutableCopy</code> are defined in different protocols (<code>NSCopying</code> and <code>NSMutableCopying</code>, respectively), and <code>NSArray</code> conforms to both. <code>mutableCopy</code> is defined for <code>NSArray</code> (not just <code>NSMutableArray</code>) and allows you to make a mutable copy of an originally immutable array:</p> <pre><code>// create an immutable array NSArray *arr = [NSArray arrayWithObjects: @"one", @"two", @"three", nil ]; // create a mutable copy, and mutate it NSMutableArray *mut = [arr mutableCopy]; [mut removeObject: @"one"]; </code></pre> <p>Summary: </p> <ul> <li>you can depend on the result of <code>mutableCopy</code> to be mutable, regardless of the original type. In the case of arrays, the result should be an <code>NSMutableArray</code>.</li> <li>you <em>cannot</em> depend on the result of <code>copy</code> to be mutable! <code>copy</code>ing an <code>NSMutableArray</code> <em>may</em> return an <code>NSMutableArray</code>, since that's the original class, but <code>copy</code>ing any arbitrary <code>NSArray</code> instance would not.</li> </ul> <p><strong>Edit:</strong> re-read your original code in light of Mark Bessey's answer. When you create a copy of your array, of course you can still modify the original regardless of what you do with the copy. <code>copy</code> vs <code>mutableCopy</code> affects whether the <em>new array</em> is mutable.</p> <p><strong>Edit 2:</strong> Fixed my (false) assumption that <code>NSMutableArray -copy</code> would return an <code>NSMutableArray</code>.</p>
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    1. POHow do copy and mutableCopy apply to NSArray and NSMutableArray?
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    1. USAsher Dunn
    1. USAsher Dunn
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    1. POHow do copy and mutableCopy apply to NSArray and NSMutableArray?
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    1. COSending -copy to an NSMutableArray does not normally return another mutable array. It certainly *could do so*, but in the usual case, it returns an immutable, constant-time access, array.
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      1. USMark Bessey
    2. COOops, you are right. I misread the OP's code and thought he was modifying the result of -copy. It would make just as much sense for NSMutableArray's -copy to return another mutable array, so I (incorrectly) assumed that was the case.
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      1. USAsher Dunn
    3. COAm I missing something as I can't find any reference to [mut remove: @"one"]; should this not be [mut removeObjectIdenticalTo: @"one"]; I just want to clarify for those reading this and trying to learn?
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      1. USfuzzygoat
 

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