title: "Cannot assign value of type 'String' to type 'AnyObject?'", Swift 3, Xcode 8 beta 6
body: <p>A fairly simple piece of code</p>
  
  <pre><code>var dict: [String: AnyObject] = [:]
  dict["key"] = "value"
  </code></pre>
  
  <p>generates the following compile-time error</p>
  
  <pre><code>Cannot assign value of type 'String' to type 'AnyObject?'
  </code></pre>
  
  <p>Simple type checks tell me that <code>String</code> is <code>AnyObject</code></p>
  
  <pre><code>"value" is AnyObject // returns true
  </code></pre>
  
  <p>I could change <code>AnyObject</code> to <code>Any</code> and everything would work</p>
  
  <pre><code>var dict: [String: Any] = [:]
  dict["key"] = "value"
  </code></pre>
  
  <p>but I want to understand why do I get the error? Is <code>String</code> no longer <code>AnyObject</code>? Or is this a bug?</p>