Example of dispatch_once in Swift

Question

Is there an example of how dispatch_once should be used in Swift? (Preferably one from Apple.)

Note: In this case, I\'m not using it for a singleton

Answer 1

For those of you who are curious, for me this approach has been useful for this purpose:

class SomeVC : UIViewController {
    private var token: dispatch_once_t = 0

    public override func viewDidAppear(animated: Bool) {
        super.viewDidAppear(animated)

        dispatch_once(&token) { () -> Void in
            self.doSomethingOnce()
        }

    }
}

By not declaring a static var it has the expected behaviour. That being said, this is definitely NOT RECOMMENDED for any serious project, since in the Docs (as your well said) it states:

The predicate must point to a variable stored in global or static scope. The result of using a predicate with automatic or dynamic storage (including Objective-C instance variables) is undefined.

If we don't want to run into any future weird bugs and undefined behaviour I would just stick to what Apple says. But it's still nice to play around with these things, isn't it? =)