1.判断是否为某类型用 is
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")
]
var movieCount = 0
var songCount = 0
for item in library {
if item is Movie{
movieCount += 1
}else if item is Song{
songCount += 1
}
}
print("There are \(movieCount) moviewsm, \(songCount) songs")
2.向下转型用 is
不确定是否成功用 is? 强制转换用 is!
for item in library {
if let movie = item as? Movie{
print("movie named:\(movie.name)")
}else if let song = item as? Song{
print("song named:\(song.name)")
}
}
3.Any 和 AnyObject的类型转换
- Any可以表示任何类型，包括函数类型。
- AnyObject可以表示任何类类型的实例。
如果想用
重要
let optionalNumber: Int? = 3
things.append(optionalNumber) // 警告
things.append(optionalNumber as Any) // 没有警告
