cocoa - 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.