title: The swift compiler always 100% CPU
body: <p>I just added a Swift extension in my old Objective-C app. The Swift compiler is always at 100% CPU and hangs after I had run several times. I had tried restarting the Mac, but it's still the same.<br>
  I run Xcode6-Beta2 on OSX 10.9.3. Thanks.</p>
  
  <p>Update:
  I found these code cause this issue:</p>
  
  <pre><code>let defaults = NSUserDefaults.standardUserDefaults() 
  let lastURLBase: String? = defaults.objectForKey("HP-lastURLBase") as String?
  </code></pre>