title: swift global constants: cannot use another constant for initialization
body: <p>Here is what I am trying to do:</p>
  
  <pre><code>class ViewController: UIViewController {
  let screenRect: CGRect = UIScreen.mainScreen().bounds
  let screenWidth = screenRect.width;
  let screenHeight = screenRect.height;
  let screenX = screenRect.origin.x
  let screenY = screenRect.origin.y
  override func viewDidLoad() {
  ...and so on
  </code></pre>
  
  <p>Swift allows me to declare <code>screenRect</code>.</p>
  
  <p>However, it does not allow me to declare any other constants using this. It shows me the error: <code>'ViewController.Type' does not have a member named 'screenRect'</code></p>
  
  <p>How do I define these constants and why does not swift allow me to use another constnt to define them.</p>