title: Use Swift extensions in Obj-C
body: <p>Is it possible to use Swift extensions in Obj-C?</p>
  
  <p>I'm extending the <code>UIView</code> class with some fade animation like this:</p>
  
  <pre><code>import Foundation
  import UIKit
  
  extension UIView {
      func fadeOut(duration: NSTimeInterval) {
          UIView.animateWithDuration(duration, delay: 0.0, options: UIViewAnimationOptions.CurveEaseOut, animations: {
              self.alpha = 0.0
              }, completion: nil)
      }
  }
  </code></pre>
  
  <p>I unsuccessfully tried to call it in my Obj-C class like</p>
  
  <pre><code>[someView fadeOut(1.0)]
  </code></pre>