What is difference between [NSObject: AnyObject] and AnyObject in swift

Question

In default template we can find the following code:

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool

Just wonder why here it is [NSObject: AnyObject]? rather than AnyObject? What's the different between them?

Answer 1

[NSObject: AnyObject] is a dictionary that allows you to access one object by providing a different object. Simply putting AnyObject means that your program doesn't know whether the parameter is a dictionary, a string, and int, or what, and therefore doesn't know how to handle it. Besides, the OS calls that method so you know you are getting a [NSObject: AnyObject] every time, so why not have the parameter type that.