Question

I have seen many people suggesting to use dispatch_once to do the singleton:

+(MyClass *)singleton {
    static dispatch_once_t pred;
    static MyClass *shared = nil;

    dispatch_once(&pred, ^{
        shared = [[MyClass alloc] init];
    });
     return shared;
}

Why is this better when it doesn’t really support true singleton, and people can still use init to create an instance and even do a release on the sharedInstance?

Apple’s way is preventing all those cases
http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CocoaFundamentals/CocoaObjects/CocoaObjects.html
I know it is not thread-safe, but I think it is easy to put a synchronize block there to make it thread-safe.

Answer 1

Why not just combine the two?

Use the function you listed instead of Apple’s + (MyGizmoClass*)sharedManager function, but implement all of the allocWithZone, copyWithZone, retain, retainCount, release, and autorelease overrides.

Lots more discussion here: What should my Objective-C singleton look like?