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copied!<p>If I understand your question correctly (given your later comment), you want to convert an immutable copy of an mutable object back to being mutable again.</p> <p>The problem seems to be this:</p> <pre><code>NSMutableString *foo = [NSMutableString stringWithString:@"a mutable object"]; NSMutableDictionary *dictionary1, *dictionary2; dictionary1 = [NSMutableDictionary dictionaryWithObject:foo forKey:@"foo"]; dictionary2 = [[NSMutableDictionary alloc]initWithDictionary:dictionary1 copyItems: YES]; [[dictionary1 objectForKey:@"foo"] appendString:@", mutated"]; [[dictionary2 objectForKey:@"foo"] appendString:@", mutated"]; </code></pre> <p>we can alter the object in dictionary1 just fine, but doing the same to dictionary2 throws an exception.</p> <p>This is because although NSMutableDictionary's initWithDictionary:copyItems: method makes a mutable copy of the dictionary object, it makes immutable copies of its contents.</p> <p>Classes that distinguish between immutable and immutable versions (such as cocoa's basic string, array & dictionary classes) are supposed to implement a copyWithZone: and mutableCopyWithZone: method. Since not all classes implement an mutableCopyWithZone: method, NSMutableDictionary's initWithDictionary:copyItems: method copies each of dictionary1's contents immutably, meaning that dictionary2 contains immutable objects.</p> <p>You can make an mutable copy of an immutable object by sending it a mutableCopy message. But probably a better solution for you would be to add an initWithDictionary:mutableCopyItems: method to NSMutableDictionary with a category:</p> <pre><code>- (id) initWithDictionary:(NSDictionary *)otherDictionary mutableCopyItems:(BOOL)flag { if (flag) { self = [self init]; if (self) for (id key in otherDictionary){ id object = [otherDictionary objectForKey:key]; if ([object respondsToSelector:@selector(mutableCopyWithZone:)]) [self setObject:[object mutableCopy] forKey:key]; else [self setObject:[object copy] forKey:key]; } } else self = [self initWithDictionary:otherDictionary]; return self; } </code></pre> <p>Read these if you want to know the difference between copy, mutableCopy, copyWithZone: and mutableCopyWithZone:</p> <p><a href="http://developer.apple.com/mac/library/documentation/Cocoa/Reference/Foundation/Protocols/NSMutableCopying_Protocol/Reference/Reference.html#//apple_ref/occ/intf/NSMutableCopying" rel="nofollow noreferrer">http://developer.apple.com/mac/library/documentation/Cocoa/Reference/Foundation/Protocols/NSMutableCopying_Protocol/Reference/Reference.html#//apple_ref/occ/intf/NSMutableCopying</a></p> <p><a href="http://developer.apple.com/mac/library/documentation/Cocoa/Reference/Foundation/Protocols/NSCopying_Protocol/Reference/Reference.html#//apple_ref/occ/intf/NSCopying" rel="nofollow noreferrer">http://developer.apple.com/mac/library/documentation/Cocoa/Reference/Foundation/Protocols/NSCopying_Protocol/Reference/Reference.html#//apple_ref/occ/intf/NSCopying</a></p>

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