Apple has added a comment about garbage-collected singletons in its Cocoa Fundamentals Guide:
http://developer.apple.com/documentation/Cocoa/Conceptual/CocoaFundamentals/CocoaObjects/chapter_3_section_10.html

Basically you create a singleton as shown in the guide's example, but in a garbage-collected environment you can leave out implementing the release, retain, retainCount, and autorelease methods.

If you follow the Apple example you will need to implement a class factory method, allocWithZone: and copyWithZone.

- Dave

On 10 Apr 2008, at 22:11, Karl Moskowski wrote:

I have a couple of classes for which I'd like to use the singleton pattern.

I read some of the old posts on this list and at cocoadev.com about approaches to take. They mention Apple's recommendations about overriding retain, release, etc. to essentially turn them into no- ops. However, they're from pre-Leopard days, and in a GC-required app, the compiler automatically no-ops those methods.

I'm currently using something like this code in my implementations:

static MyClass *sharedInstance;
+ (MyClass *)sharedInstance {
        if (!sharedInstance)
                sharedInstance = [[self alloc] init];
        return sharedInstance;
}

- (id)init {
        if (!sharedInstance)
                sharedInstance = [super init];
        return sharedInstance;
}

My goal is to ensure that [MyClass sharedInstance] and [[MyClass alloc] init] return the same singleton object. Furthermore, I'd like to ensure that an object instantiated in a NIB is the sharedInstance too. So far, it seems to work, but I'm afraid I've missed something.

Any suggestions? Thanks.

----
Karl Moskowski <[EMAIL PROTECTED]>
Voodoo Ergonomics Inc. <http://voodooergonomics.com/>

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