Is releasing memory of Objective-c 2.0 properties required?

Question

Something I have been wondering about properties for a while. When you are using properties, do you need to override the release message to ensure the properties are released properties?

i.e. is the following (fictitious) example sufficient?

@interface MyList : NSObject {
NSString* operation;
NSString* link;
}
@property (retain) NSString* operation;
@property (retain) NSString* link;
@end

@implementation MyList
@synthesize operation,link;
@end

Answer 1

You should always release the backing variables in dealloc:

- (void) dealloc {
   [operation release];
   [link release];

   [super dealloc];
}

Another way:

- (void) dealloc {
   self.operation = nil;
   self.link = nil;

   [super dealloc];
}

That's not the preferred way of releasing the objects, but in case you're using synthesized backing variables, it's the only way to do it.

NOTE: to make it clear why this works, let's look at the synthesized implementation of the setter for link property, and what happens when it is set to nil:

- (void) setLink:(MyClass *) value {
   [value retain]; // calls [nil retain], which does nothing
   [link release]; // releases the backing variable (ivar)
   link = value;   // sets the backing variable (ivar) to nil
}

So the net effect is that it will release the ivar.

Answer 2

In non-GC applications, yes. It is usual to assign nil instead of releasing the ivars. My best experience is to release ivars initialized with init and assign nil to properties with retain and copy mode.

In your case I would assign nil

- (void) dealloc {
   self.operation = nil;
   self.link = nil;
   [super dealloc];
}