title: why is performSelector not present in swift
body: <p>apparently the following is not available in swift anymore:</p>
  
  <pre><code>[self performSelector:@selector(onFlip) withObject:nil afterDelay:0.3];
  </code></pre>
  
  <p>why is this the case if the following is still present:</p>
  
  <pre><code>NSObject.cancelPreviousPerformRequestsWithTarget(self, selector: singleTapSelector, object: nil)
  </code></pre>
  
  <p>doesn't nsobject.cancel work with performSelector? why have the cancel functionality but not the perform functionality?</p>