Question

Is there any built-in function that allows me to deep copy an NSMutableArray?

I looked around, some people say [aMutableArray copyWithZone:nil] works as deep copy. But I tried and it seems to be a shallow copy.

Right now I am manually doing the copy with a for loop:

//deep copy a 9*9 mutable array to a passed-in reference array  -deepMuCopy : (NSMutableArray*) array      toNewArray : (NSMutableArray*) arrayNew {      [arrayNew removeAllObjects];//ensure it's clean      for (int y = 0; y<9; y++) {         [arrayNew addObject:[NSMutableArray new]];         for (int x = 0; x<9; x++) {             [[arrayNew objectAtIndex:y] addObject:[NSMutableArray new]];              NSMutableArray *aDomain = [[array objectAtIndex:y] objectAtIndex:x];             for (int i = 0; i<[aDomain count]; i++) {                  //copy object by object                 NSNumber* n = [NSNumber numberWithInt:[[aDomain objectAtIndex:i] intValue]];                 [[[arrayNew objectAtIndex:y] objectAtIndex:x] addObject:n];             }         }     } } 

but I’d like a cleaner, more succinct solution.

Answer 1

As the Apple documentation about deep copies explicitly states:

If you only need a one-level-deep copy:

NSMutableArray *newArray = [[NSMutableArray alloc]                               initWithArray:oldArray copyItems:YES]; 

The above code creates a new array whose members are shallow copies of the members of the old array.

Note that if you need to deeply copy an entire nested data structure — what the linked Apple docs call a true deep copy — then this approach will not suffice. Please see the other answers here for that.