what is the "as" keyword in swift

Question

I am quite new to Swift and iOS.

I am just reading some sample codes. There is a line I cannot understand:

let splitViewController = self.window!.rootViewController as UISplitViewController

What does "as" do here?

Thanks

Answer 1

You use the as keyword to cast data types. UIWindow rootViewController is of type UIViewController. You downcast it to UISplitViewController.