Stored Property in Swift Extension

StoredProperty.swift

import ObjectiveC

// Declare a global var to produce a unique address as the assoc object handle
var AssociatedObjectHandle: UInt8 = 0

extension CCNode {
    var previousX: CGFloat? {
        get {
            return objc_getAssociatedObject(self, &AssociatedObjectHandle) as? CGFloat
        }
        set {
            objc_setAssociatedObject(self, &AssociatedObjectHandle, newValue, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
        }
    }
    
    var previousY: CGFloat? {
        get {
            return objc_getAssociatedObject(self, &AssociatedObjectHandle) as? CGFloat
        }
        set {
            objc_setAssociatedObject(self, &AssociatedObjectHandle, newValue, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
        }
    }
}