Question

I’m writing my very first steps in Objective-C.
I followed some examples and the official documentation, and am using autoreleased objects* without explicitly declaring an NSAutoReleasePool.

* By autoreleased objects I mean: SomeClass *obj = [SomeClass someClass];

Is it ok to do it this way?
Will it cause a memory problem?
Is declaring a NSAutoReleasePool more efficient?

edit: I made a mistake in the code example, what I meant was getting an object by it’s class factory method instead of allocing an instance of it. This factory methods [often|always] return autoreleased objects, right? for example: [NSString stringWithCString:x]

Answer 1

You don’t need to create an autorelease pool explicitly usually. When you do normal Mac programming using the AppKit framework, there will be an implicit autorelease pool which is handled by the event loop. You need to concern yourself with autorelease pools mainly on two occasions:

• Your code runs in a background thread: If you have a background thread there is no autorelease pool created for you and you will have to do this manually.
• You have a tight loop where you create and destroy a lot of objects. If in this loop any objects are autoreleased they will not actually be released until the autorelease pool is drained. This means that your memory consumption will rise, even though you don’t reference those objects anymore. In this situation having a local autorelease pool can help with performance, although switching from autoreleasing to explicit retain/release is probably more efficient.