Autorelease vs. release

Question

When I need an array for temporary use, what's the difference between these:

1:

NSMutableArray *stuff = [[NSMutableArray alloc] init];
// use the array
[stuff release];

2:

NSMutableArray *stuff = [NSMutableArray array];
// use the array

3:

NSMutableArray *stuff = [[[NSMutableArray alloc] init] autorelease];
// use the array

I prefer number 2, since it's shorter. Are there any good reasons to use number 1 or 3?

Anachronistic

Answer 1

Number 2 is likely the best choice in most cases.

Number 1 has the chance of losing the release at some point down the line, for whatever reason, but it does release the array immediately, which in memory-starved environments can be useful.

Number 3 is basically a verbose equivalent of number 2, but it does come in handy if you want to use an initWith* that doesn't have a corresponding arrayWith*.

Note: If you are memory-starved, such as in an expensive loop where you need a fresh array for each iteration; don't release and allocate new arrays; just use -removeAllObjects and recycle the array.

Exposure

Thanks! Good point about the immediate release of memory in number 1. – Anachronistic

On the iPhone, you'll find most people use number 1 because the memory gets given back to the runtime sooner. In fact, Apple recommend avoiding autorelease as much as possible (on the iPhone). – Scalpel

Good answer, save for the last bit. I'd wager that the difference between creating a new array on each pass and removing all objects is immeasurable and, quite likely, removing all objects will be trivially slower. In any case, don't optimize until you have a quantified performance problem. – Cowley

@bburn: How could removing all objects be slower than releasing the array; as the former is a part of the process for the latter? – Exposure