Type Casting

Defining a Class Hierarchy for Type Casting

                  class MediaItem {

    var name: String

    init(name: String) {

        self.name = name

    }

}
                

                  class Movie: MediaItem {

    var director: String

    init(name: String, director: String) {

        self.director = director

        super.init(name: name)

    }

}



class Song: MediaItem {

    var artist: String

    init(name: String, artist: String) {

        self.artist = artist

        super.init(name: name)

    }

}
                

                  let library = [

    Movie(name: "Casablanca", director: "Michael Curtiz"),

    Song(name: "Blue Suede Shoes", artist: "Elvis Presley"),

    Movie(name: "Citizen Kane", director: "Orson Welles"),

    Song(name: "The One And Only", artist: "Chesney Hawkes"),

    Song(name: "Never Gonna Give You Up", artist: "Rick Astley")

]

// the type of "library" is inferred to be [MediaItem]
                

Checking Type

                  var movieCount = 0

var songCount = 0



for item in library {

    if item is Movie {

        movieCount += 1

    } else if item is Song {

        songCount += 1

    }

}



print("Media library contains \(movieCount) movies and \(songCount) songs")

// Prints "Media library contains 2 movies and 3 songs"
                

Downcasting

                  for item in library {

    if let movie = item as? Movie {

        print("Movie: \(movie.name), dir. \(movie.director)")

    } else if let song = item as? Song {

        print("Song: \(song.name), by \(song.artist)")

    }

}



// Movie: Casablanca, dir. Michael Curtiz

// Song: Blue Suede Shoes, by Elvis Presley

// Movie: Citizen Kane, dir. Orson Welles

// Song: The One And Only, by Chesney Hawkes

// Song: Never Gonna Give You Up, by Rick Astley
                

Type Casting for Any and AnyObject

                  var things = [Any]()



things.append(0)

things.append(0.0)

things.append(42)

things.append(3.14159)

things.append("hello")

things.append((3.0, 5.0))

things.append(Movie(name: "Ghostbusters", director: "Ivan Reitman"))

things.append({ (name: String) -> String in "Hello, \(name)" })
                

                  for thing in things {

    switch thing {

    case 0 as Int:

        print("zero as an Int")

    case 0 as Double:

        print("zero as a Double")

    case let someInt as Int:

        print("an integer value of \(someInt)")

    case let someDouble as Double where someDouble > 0:

        print("a positive double value of \(someDouble)")

    case is Double:

        print("some other double value that I don't want to print")

    case let someString as String:

        print("a string value of \"\(someString)\"")

    case let (x, y) as (Double, Double):

        print("an (x, y) point at \(x), \(y)")

    case let movie as Movie:

        print("a movie called \(movie.name), dir. \(movie.director)")

    case let stringConverter as (String) -> String:

        print(stringConverter("Michael"))

    default:

        print("something else")

    }

}



// zero as an Int

// zero as a Double

// an integer value of 42

// a positive double value of 3.14159

// a string value of "hello"

// an (x, y) point at 3.0, 5.0

// a movie called Ghostbusters, dir. Ivan Reitman

// Hello, Michael
                

                  let optionalNumber: Int? = 3

things.append(optionalNumber)        // Warning

things.append(optionalNumber as Any) // No warning