title: Issue when the initialization method's parameter with default value
body: <p>I am make a init method in my project for a certain class, basically I want to wrap a local Notification class.</p>
  
  <p>Because my local notification has only one sound and I want to put it as a default when the class is initialized as following:</p>
  
  <p></p>
  
  <pre><code>    override init(notificationTitle:String, subtitle:String, sound = UNNotificationSound.init(named: AppSettingManager.share.loadFocusNotificationSound()), categoryId:String ) {
  
      super.init()
  }
  </code></pre>
  
  <p>because the sound parameter's value is store in the NSUserdefault and I want to set the sound's value when the class is initialized.</p>
  
  <p>However, Xcode complains as </p>
  
  <blockquote>
    <p>Unnamed parameters must be written with the empty name '_'</p>
  </blockquote>
  
  <p><a href="https://i.stack.imgur.com/DHE45.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/DHE45.png" alt="enter image description here"></a></p>
  
  <p>How can I approach this? Any other way to solve this? thanks in advance.</p>