Sometimes it is helpful to pull information out of a dictionary and put it into an array. Suppose, for example, that you want to list all of the movies that have been rated (without their ratings).
In this case, it makes sense to create an instance of the Array type with the keys from your dictionary.
Listing 10.12 Sending keys to an array
import Cocoa var movieRatings = ["Donnie Darko": 4, "Chungking Express": 5, "Dark City": 4] print("I have rated \(movieRatings.count) movies.") let darkoRating = movieRatings["Donnie Darko"] movieRatings["Dark City"] = 5 movieRatings let oldRating: Int? = movieRatings.updateValue(5, forKey: "Donnie Darko") if let lastRating = oldRating, let currentRating ...