MKReverseGeocoder autorelease/release question in Apple's CurrentAddress sample

Question

I am looking at this code lifted straight from the MapViewController.m file in the CurrentAddress sample available on Apple's web site:

- (void)dealloc
{
    [reverseGeocoder release];
    [mapView release];
    [getAddressButton release];

    [super dealloc];
}

- (IBAction)reverseGeocodeCurrentLocation
{
    self.reverseGeocoder =
        [[[MKReverseGeocoder alloc] initWithCoordinate:mapView.userLocation.location.coordinate] autorelease];
    reverseGeocoder.delegate = self;
    [reverseGeocoder start];
}

I am wondering what the function is of the autorelease when allocating the object. (The reverseGeocoder is an ivar in the MapViewController class set up with the retain property.) I have code similar to this in my application, and it seems to work either way.

Answer 1

Setting your reverseGeocoder property increments the retain count (+1), but since you're creating the object with alloc+init (+1), you need to autorelease (-1) so that you do not end up with a 2 retain count.

It does work either way, the only difference is that when you do not autorelease, you leak.

The reverseGeocoder is an ivar

It sure is, but note that when you're using the self.reverseGeocoder form, you're not accessing the ivar directly - instead, you're calling the relevant setReverseGeocoder: function, that is either written by yourself or @synthesized by the compiler.

See: http://developer.apple.com/library/mac/#documentation/cocoa/conceptual/MemoryMgmt/MemoryMgmt.html

And: What equivalent code is synthesized for a declared property?