type_casting.swift

let mediaSet: [Media] = [Video(url: "http://www_123_@1x.png", thumb: "http://www_123_@1x.png"),
                         Video(url: "http://www_123_@1x.png", thumb: "http://www_123_@1x.png"),
                         Media(url: "http://www_123_@1x.png")]

for media in mediaSet {
    // We don't sure about casting result
    if let video = media as? Video {
        print("Video: \(video)")
    }
    
    switch media {
    case is Video:
        // We are sure about casting result, because we checked it before
        let video = media as! Video
        print("Video: \(video)")
    default:
        break
    }
}