title: How to assign one class type instance to another class type reference in swift to apply dynamic polymorphism
body: <p>iam unable to set backgroundcolor for label at runtime</p>
  
  <pre><code>func example() {
    let lbl: UILabel = UILabel()
    let arrTemp: NSMutableArray = NSMutableArray()
    arrTemp.addObject(lbl)
    let tempButton: UIButton? = arrTemp.objectAtIndex(0) as? UIButton
    tempButton.backgroundColor = UIColor.whiteColor()
  }
  </code></pre>