Correct Singleton Pattern Objective C (iOS)?

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Keep it simple:

+(instancetype)sharedInstance
{
    static dispatch_once_t pred;
    static id sharedInstance = nil;
    dispatch_once(&pred, ^{
        sharedInstance = [[self alloc] init];
    });
    return sharedInstance;
}

- (void)dealloc
{
    // implement -dealloc & remove abort() when refactoring for
    // non-singleton use.
    abort();
}

That is it. Overriding retain, release, retainCount and the rest is just hiding bugs and adding a bunch of lines of unnecessary code. Every line of code is a bug waiting to happen. In reality, if you are causing dealloc to be called on your shared instance, you have a very serious bug in your app. That bug should be fixed, not hidden.

This approach also lends itself to refactoring to support non-singleton usage modes. Pretty much every singleton that survives beyond a few releases will eventually be refactored into a non-singleton form. Some (like NSFileManager) continue to support a singleton mode while also supporting arbitrary instantiation.

Note that the above also “just works” in ARC.

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