title: Extending Array of a specific type
body: <p>I already searched here and I hope, I didn't miss any post, but I couldn't find a answer for this question:</p>
  
  <p>I want to extend an array of a specific type, in my case only an array of [String].</p>
  
  <p>How do I do that?</p>
  
  <pre><code>extension [String] { ...
  </code></pre>
  
  <p>doesn't work.</p>