title: how to increment a swift int enumeration
body: <p>I have a swift enumeration</p>
  
  <pre><code> enum MainState : Int {
       case NotStarted
       case Init
       case AskWhatToText
       case RecordWhatToText
   }    
   var state = MainState.NotStarted
  </code></pre>
  
  <p>and would like to do something like </p>
  
  <pre><code>state++
  </code></pre>
  
  <p>but get an error. suggestions?</p>