title: How to extract differences between dictionaries?
body: <p>I can compare whether 2 dictionaries match or not like this:</p>
  
  <pre><code>func ==(lhs: [String: AnyObject], rhs: [String: AnyObject] ) -&gt; Bool {
      return NSDictionary(dictionary: lhs).isEqualToDictionary(rhs)
  }
  </code></pre>
  
  <p>Is there a concise way to extract the differences between 2 dictionaries, as in the opposite of the intersection?</p>