Question

I am currently playing around with ARC a bit to get some things figured out, before starting to do the actual work. I did setup this code:

NSNumber* n = [[NSNumber alloc] initWithInt:3];
__weak NSNumber* weakN = n;
n = nil;
NSLog(@">>>: %@ %@", n, weakN);

I expected n and weakN to be nil, as n = nil; should trigger a release in my eyes? Unfortunately it doesn’t. The output is “>>>: (null) 3”. What am I missing here?

Another thing is, that I am pretty sure, the below code was giving me a hard time when starting with arc:

__weak NSNumber* weakN2 = [[NSNumber alloc] initWithInt:3];
NSLog(@">>>: %@", weakN2);

I am pretty sure, I’ve had some problems with similar code, as arc would release the object straight after initialization, as there is no strong reference to the object. Unfortunately, the output of the above is “>>>: 3”.

It would be great to get some clarification on this stuff. I am clearly missing something here!

Best regards,
Michael

Answer 1

In addition to what kevboh said, it’s also rather pointless to create weak references to simple immutable Foundation objects like NSNumber. For performance reasons, Foundation might well vend you a cached object instead of creating an entirely new one. And if it doesn’t now, then it might in some future release.

The upshot is that you’re probably not the sole owner of the object returned by [[NSNumber alloc] initWithInt:3], no matter what you think.