How to prevent lazy loading of static variables in Swift

Question

I wrote a Swift utility class in which I define several static methods and a private static constant. However, I wish this constant to be loaded immediately after the class is referenced for the first time, as opposed to lazily. The only thing I can think of doing is to reference the static constant in every single static function like this:

private static let myObserver: Observer = {
    let observer = Observer(actionToPerform: foo1)
    SomeOtherClass.register(observer)
    return observer
}()

static func foo1() {
    _ = myObserver
    ...
}

static func foo2() {
    _ = myObserver  
    ...
}

static func foo3() {
    _ = myObserver
    ...
}

//even more of a hassle:
static let myIntConstant: Int = {
    _ = myObserver
    return 5
} ()

.
.
.

However, that solution looks pretty ugly. Is there a cleaner way? Some sort of class initialization callback I can use?

@Mohammadalijf That's always a possibility. But I'm curious to know if there's a solution for just static stuff. — Hans Brende
– Hans Brende, Commented Dec 12, 2016 at 6:59

Hans Brende · Accepted Answer · 2016-12-12 07:58:44Z

4

Ok, I seem to have found a workable solution to my own question.

Ensure that the class is a subclass of NSObject.
Insert the following code:

override class func initialize() { 
     _ = myObserver
}

After doing this, the static constant is loaded immediately after the class is referenced, as desired.

Of course, this approach is limited by the fact that the class must be a subclass of NSObject, which may not be possible for all such classes. Any other potential drawbacks to this approach would be welcomed!

edited Dec 12, 2016 at 7:58

answered Dec 12, 2016 at 7:46

Hans Brende

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2 Comments

Anton Strogonoff Over a year ago

Yeah, I was wrong in my original answer because naturally if you use Swift on iOS you must be able to inherit from NSObject and have access to initialize(). It does have a bit of a “magicky” feel to it if you ask me but it’s officially documented and NSHipster has some articles on this it shouldn’t be too bad.

rshev Over a year ago

Seems to be not permitted in Swift anymore: Method 'initialize()' defines Objective-C class method 'initialize', which is not permitted by Swift

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