Proper way to return an array

Question

Hey there,

I never seem to get this right. I've got a method that returns a mutable array. What is the proper way to return the array and avoid potential memory leaks?

If I plan to store the results locally inside another view controller, does that affect the way the array should be returned?

Lastly, what if it's just an non-mutable array? Does that require a different technique?

thanks, Howie

Answer 1

For a NSMutableArray I would use:

-(NSMutableArray*)getMyArray
{
   NSMutableArray *retval = [[NSMutableArray alloc] init];
   // do your stuff w/ array
   return [retval autorelease];
}

The caller of this code may want to retain the returned array, since it is autoreleased.

Answer 2

Return an auto-released object. If you've created your array with any alloc/init/copy methods - you should send autorelease message to array before returning it (something like return [myArray autorelease];). Otherwise arrays created with factory methods (arrayFrom... arrayWithContentsOf...) return autoreleased object so you don't need to worry about memory leaks there.

You should read about memory management and retain count on apple dev site. There might be some other initialization methods that retain returned object which would 'cause a memory leak.

Answer 3

If your method does not have alloc or copy in the name then the proper thing is to return a autoreleased version of the array. Also, you should return a copy of the array to prevent modifications to your local copy

- (NSMutabalArray*] mutableArray {
    return [[myArray mutableCopy] autorelease];
}

- (NSArray*] array {
    return [[myArray copy] autorelease];
}