title: What is difference between [NSObject: AnyObject] and AnyObject in swift
body: <p>In default template we can find the following code:</p>
  
  <p><code>func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -&gt; Bool</code></p>
  
  <p>Just wonder why here it is [NSObject: AnyObject]? rather than AnyObject? What's the different between them?</p>