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]
检查类型
var movieCount = 0 var songCount = 0 for item in library { if item is Movie { ++movieCount } else if item is Song { ++songCount } } print("Media library contains \(movieCount) movies and \(songCount) songs") // prints "Media library contains 2 movies and 3 songs"
向下转型
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
Any与AnyObject类型转换
let someObjects: [AnyObject] = [ Movie(name: "2001: A Space Odyssey",director: "Stanley Kubrick"),Movie(name: "Moon",director: "Duncan Jones"),Movie(name: "Alien",director: "Ridley Scott") ] for object in someObjects { let movie = object as! Movie print("Movie: '\(movie.name)',dir. \(movie.director)") } // Movie: '2001: A Space Odyssey',dir. Stanley Kubrick // Movie: 'Moon',dir. Duncan Jones // Movie: 'Alien',dir. Ridley Scott
for movie in someObjects as! [Movie] { print("Movie: '\(movie.name)',dir. Ridley Scott
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
版权声明:本文内容由互联网用户自发贡献,该文观点与技术仅代表作者本人。本站仅提供信息存储空间服务,不拥有所有权,不承担相关法律责任。如发现本站有涉嫌侵权/违法违规的内容, 请发送邮件至 dio@foxmail.com 举报,一经查实,本站将立刻删除。