Is it possible to allow didSet to be called during initialization in Swift?

Create an own set-Method and use it within your init-Method:

class SomeClass {
    var someProperty: AnyObject! {
        didSet {
            //do some Stuff
        }
    }

    init(someProperty: AnyObject) {
        setSomeProperty(someProperty)
    }

    func setSomeProperty(newValue:AnyObject) {
        self.someProperty = newValue
    }
}

By declaring someProperty as type: AnyObject! (an implicitly unwrapped optional), you allow self to fully initialize without someProperty being set. When you call setSomeProperty(someProperty) you're calling an equivalent of self.setSomeProperty(someProperty). Normally you wouldn't be able to do this because self hasn't been fully initialized. Since someProperty doesn't require initialization and you are calling a method dependent on self, Swift leaves the initialization context and didSet will run.

If you use defer inside of an initializer, for updating any optional properties or further updating non-optional properties that you've already initialized and after you've called any super.init() methods, then your willSet, didSet, etc. will be called. I find this to be more convenient than implementing separate methods that you have to keep track of calling in the right places.

For example:

public class MyNewType: NSObject {

    public var myRequiredField:Int

    public var myOptionalField:Float? {
        willSet {
            if let newValue = newValue {
                print("I'm going to change to \(newValue)")
            }
        }
        didSet {
            if let myOptionalField = self.myOptionalField {
                print("Now I'm \(myOptionalField)")
            }
        }
    }

    override public init() {
        self.myRequiredField = 1

        super.init()

        // Non-defered
        self.myOptionalField = 6.28

        // Defered
        defer {
            self.myOptionalField = 3.14
        }
    }
}

Will yield:

I'm going to change to 3.14
Now I'm 3.14