release/autorelease confusion in cocoa for iphone

Question

I\'m slowly teaching myself cocoa for the iPhone(through the Stanford Class on iTunes U) and I\'ve just gone through the part on memory management, and I wanted to hopefully

Answer 1

1. I've never released string constants like NSString *foo = @"x";. Logically, if you had to release the result of that, it you would have to release the parameter to initWithString, and both the parameters to initWithFirstName:lastName:, too.
2. You must do release or autorelease firstName and lastName. I've seen warnings about not using property syntax in destructors, which I think is the same reason you don't use virtual functions in C++ constructors and destructors.

Your assumption was wrong. You must do either this:

    Person *Me = [[Person alloc] initWithFirstName: @"Drew"
                                          lastName: @"McGhie"];
    ...
    [Me release];

or this:

    Person *Me = [Person personWithFirstName: @"Drew"
                                    lastName: @"McGhie"];

...and make sure your Person object handles +personWithFirstName:lastName: correctly, i.e. [[[self alloc] initWithFirstName: firstName lastName: lastName] autorelease].

You should probably do the one with less code. Clarity is important, NSAutoreleasePool will probably never be your bottleneck, and if it ever is it's easily fixed.

I think people put a lot of effort into avoiding the class messages that return an autorelease'd object that just isn't merited. It's premature optimization, in that it probably isn't necessary and may not even be the correct thing to do. And it's harder to maintain, you'll very likely be chasing leaks forever.

Also, you're going to autorelease an object you had to init (i.e. alloc + initPersonWithFirstName:lastName: instead of using a class message like personWithFirstName:lastName:), I'd suggest you do it immediately. Otherwise, you're potentially chasing that same kind of leak. So if you're not going to add a personWithFirstName:lastName: method to Person, do this instead:

    Person *Me = [[[Person alloc] initWithFirstName: @"Drew"
                                           lastName: @"McGhie"] autorelease];

Summary: Cocoa does a lot to help you with memory management. Make sure you don't fight it.

Updated based on Jon's feedback in comment.