[iPhone SDK] property/retain count mystery

Question

I'm confused as to the behavior of the following code:
UIViewController *viewController = [[UIViewController alloc] init];
UITabBarItem *barItem = [[UITabBarItem alloc] initWithTabBarSystemItem:UITabBarSystemItemContacts tag:1];
printf("1: %d
", barItem.retainCount); // is 1 as expected
viewController.tabBarItem = barItem;
printf("2: %d
", barItem.retainCount); // is 2 as expected
viewController.tabBarItem;
printf("3: %d
", barItem.retainCount); // expected 2 but got 3
[viewController.tabBarItem release]; // seems that accessing the tabBarItem increments the retain count, then release decrements it - so this is a noop
printf("4: %d
", barItem.retainCount); // still 3
output is:
1: 1
2: 2
3: 3
4: 3
It appears as if just calling viewController.tabBarItem increments the retain count? (fwiw same thing happens if I call [viewController tabBarItem])
I know that the tabBarItem @property of UIViewController has the retain attribute, but that means every time I access the property's getter, I'm issuing a retain? I thought it would only retain when set.
What am I missing here?
Thanks!

Answer 1

Thanks for the tips - looks like that's what's happening. Rereading the memory management guide more carefully, under Accessor Methods I see:
For simple object values, getters and setters can be written in one of the following three ways:
1. Getter retains and autoreleases the value before returning it; setter releases the old value and retains (or copies) the new value.
2. Getter returns the value; setter autoreleases the old value and retains (or copies) the new value.
3. Getter returns the value; setter releases the old value and retains (or copies) the new value.
The tabBarItem method must be implemented as #1. Still trying to get my head around an example where this would be necessary, but thanks for the help.