Question

I’ve run into some unfamiliar Objective-c memory management code. What is the difference between:

// no property declared for myMemberVariable in interface
id oldID = myMemberVariable;
myMemberVariable = [MyMemberVariable alloc] init];
[oldID release];

and:

// (nonatomic, retain) property is declared for myMemberVariable in interface
self.myMemberVariable = [[MyMemberVariable alloc] init];

Thanks!

Answer 1

The second is technically incorrect, but the first probably stems from someone yet to embrace Objective-C 2.0 property syntax. It was added relatively recently if you’re a long-time OS X developer (or an even-longer-time NextStep/OS X developer), so you do see people not using it without gaining any benefit or detriment by not doing so.

So the first is basically the same as:

[myMemberVariable release];
myMemberVariable = [[MyMemberVariable alloc] init];

Given that you have a ‘retain’ property, the correct version with the setter should be:

// this'll be retained by the setter, so we don't want to own what we pass in
self.myMemberVariable = [[[MyMemberVariable alloc] init] autorelease];