title: Default Implementation of Objective-C Optional Protocol Methods
body: <p>How can I provide default implementations for Objective-C optional protocol methods?</p>
  
  <p>Ex.</p>
  
  <pre><code>extension AVSpeechSynthesizerDelegate {
    func speechSynthesizer(synthesizer: AVSpeechSynthesizer, didFinishSpeechUtterance utterance: AVSpeechUtterance) {
      print("&gt;&gt;&gt; did finish")
    }
  }
  </code></pre>
  
  <p>Expectation: Whatever class that conforms to <code>AVSpeechSynthesizerDelegate</code> should run the above function whenever a speech utterance finishes.</p>