title: Class function in swift extension (category)
body: <p>Is it possible to define a class function in an extension in swift, just like in an objective-C category you can also define class functions?</p>
  
  <p>Example in objective-c</p>
  
  <pre><code>@implementation UIColor (Additions)
  
  + (UIColor)colorWithHexString:(NSString *)hexString
  {
      // create color from string
      // ... some code
      return newColor;
  }
  
  @end
  </code></pre>
  
  <p>what would be the equivalent in swift?</p>