title: Expected Pattern error in Swift?
body: <p>I have been following Swift App Tutorial created by Apple <a href="https://developer.apple.com/library/content/referencelibrary/GettingStarted/DevelopiOSAppsSwift/ImplementingACustomControl.html#//apple_ref/doc/uid/TP40015214-CH19-SW1" rel="noreferrer">here</a>. Specifically, I am trying to set up a few custom buttons to create a rating control. The buttons have three images associated with it: emptyStar, filledStar, and highlightedStar, to be used at different states of the button.</p>
  
  <p>I use the code exactly as provided by Apple, but I don't know why I have been getting this compile-time cryptic error <code>Expected pattern</code> as shown in the screenshot:
  <a href="https://i.stack.imgur.com/wTSOz.png" rel="noreferrer"><img src="https://i.stack.imgur.com/wTSOz.png" alt="Expected pattern errors"></a>
  <a href="https://i.stack.imgur.com/T6OC7.png" rel="noreferrer"><img src="https://i.stack.imgur.com/T6OC7.png" alt="Image Assets"></a></p>
  
  <p>What am I doing wrong here?</p>