Where to release copy in setter?

Question

In my setter I have a incoming string that I am copying to avoid any trouble should the original be modified.

- (void)setName:(NSString *)newName{
    if(name != newName) {
     [name release];
     name = [newName copy];
    }
}

My question is: as I am doing a copy where should I release it, or do I just do an autorelease? i.e.

- (void)setName:(NSString *)newName{
    if(name != newName) {
     [name release];
     name = [[newName copy] autorelease];
    }
}

gary

Answer 1

When you do a copy, the object will be retained. This is what you want. If you autorelease it, it will be deallocated eventually. So your first example is correct. The second one will crash your app.

If you're worried about what happens when the object is deallocated, remember that you should release any references in your dealloc method.

Answer 2

Your first sample is correct:

- (void)setName:(NSString *)newName{
    if(name != newName) {
        [name release];
        name = [newName copy];
    }
}

but as you suspect, the copy must be balanced with a release. Assuming name has the usual semantics (i.e. you want it to stay around until the instance of the containing class is deallocated), the balancing release should come in dealloc (assuming you're not using Garbage Collection):

- (void)dealloc {
    [name release];
    //release other instance variables of type id

    [super dealloc];
}

Re-read the Memory Management Programming Guide for Cocoa if you're still confused.

Answer 3

In my setter I have a incoming string that I am copying to avoid any trouble should the original be modified.

- (void)setName:(NSString *)newName{
  if(name != newName) {
   [name release];
   name = [newName copy];
  }
}

My question is: as I am doing a copy where should I release it, or do I just do an autorelease? i.e.

- (void)setName:(NSString *)newName{
  if(name != newName) {
   [name release];
   name = [[newName copy] autorelease];
  }
}

As I said on your other question, autorelease translates to “send yourself release later”. That means that it counts as a release.

So, your second example releases the old value of name (good), then makes a copy of the new one (good), then puts the new one in line to be released (bad), then puts this now-doomed object into the instance variable (really bad).

The first example is correct, because you still hold a retention on the object after you put it in the instance variable.

As I also said on your other question, I think you should review the memory-management rules.

Answer 4

Your first example is correct. So is Peter Hosey – you should better familiarise yourself with the memory management rules.

If it helps, my preferred approach as it looks a little cleaner:

- (void)setName:(NSString *)name
{
  name = [name copy];
  [_name release];
  _name = name;
}