title: (String: AnyObject) does not have a member named 'subscript'
body: <p>I've been through similar questions but still do not understand why my code is throwing an error.</p>
  
  <pre><code>var dict = [String:AnyObject]()
  dict["participants"] = ["foo", "bar"]
  dict["participants"][0] = "baz"
  </code></pre>
  
  <p>The error is on line 3: <code>(String: AnyObject) does not have a member named 'subscript'</code></p>
  
  <p>I'm setting the <code>participants</code> key to an array and then trying to update the first element of it without any luck. The code above is shortened for example purposes, but I am using <code>[String:AnyObject]</code> because it is not only arrays that are stored in the dictionary.</p>
  
  <p>It's probably something really trivial but I am still new to Swift. Thanks for any help in advance!</p>