gravityForSO.swift

class FloaterContainerLayer:CALayer {
    
    var maxFloaters = 9
    var image:String?
    var velocity:CGFloat = 50.0
    
    var gravity : Gravity = "FloaterContainerLayer" // just so that the initialiser doesnt complain
}

class SomeViewController : UIViewController {
    
    lazy var dotLayer : FloaterContainerLayer = {
        let scrollLayer = FloaterContainerLayer()
        scrollLayer.bounds = self.view.layer.bounds
        scrollLayer.position = CGPoint(x: self.view.bounds.size.width/2, y: self.view.bounds.size.height/2)
        scrollLayer.image = "dot"
        scrollLayer.gravity = Gravity.dotGravity
        
        return scrollLayer
    }()
}


class Gravity : StringLiteralConvertible {
    
    static var dotGravity : Gravity = "dotLayerGravity"
    static var otherGravity : Gravity = "otherLayerGravity"
    static var lastGravity : Gravity = "lastLayerGravity"
    
    private var identifier : String = ""
    private var inMemory : CGFloat?
    
    var value: CGFloat {
        get {
            if let inMemory = inMemory {
                return inMemory
            } else {
                let fetchedGravity = (NSUserDefaults.standardUserDefaults().objectForKey(identifier) as? NSNumber) ?? 10
                inMemory = CGFloat(fetchedGravity)
                return inMemory!
            }
        }
        set(value) {
            NSUserDefaults.standardUserDefaults().setValue(value, forKey: identifier)
            // setting this to nil will make it fetch from permanenent storage.
            inMemory = nil
        }
    }
    
    typealias ExtendedGraphemeClusterLiteralType = StringLiteralType
    typealias UnicodeScalarLiteralType = StringLiteralType
    
    required init(stringLiteral value: String) {
        self.identifier = value
    }
    
    required init(unicodeScalarLiteral value: UnicodeScalarLiteralType) {
        self.identifier = "\(value)"
    }
    
    required init(extendedGraphemeClusterLiteral value: ExtendedGraphemeClusterLiteralType) {
        self.identifier = value
    }
}