第十九章 类型转换
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("movie count = \(movieCount), and song count = \(songCount)")
for item in library {
if let movie = item as? Movie {
print("Movie: '\(movie.name)', director. \(movie.director)")
} else if let song = item as? Song {
print("Song: '\(song.name)', artist. \(song.artist)")
}
}
var things = [Any]()
things.append(0)
things.append(0.0)
things.append(42)
things.append("hello")
things.append((3.0, 5.0))
things.append(["Alice": "Chips"])
things.append(Movie(name: "shimianmaifu", director: "zhangyimou"))
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"))
case let dict as Dictionary<String, String>:
for (name, favor) in dict {
print("\(name)'s favorite food is \(favor)")
}
default:
print("something else")
}
}
