title: Is it necessary to use [unowned self] in closures of UIView.animateWithDuration(...)?
body: <pre><code>    UIView.animateWithDuration(1,
          animations: { [unowned self] in
              self.box.center = self.boxTopRightPosition
          },
          completion: { [unowned self] completed in
              self.box.hidden = true
      })
  </code></pre>
  
  <p>Is it necessary to avoid memory leak?</p>