在Swift中，我们还可以给类、结构、枚举等自定义下标（subscript）

struct ChannelModel {

    var channelName: String

    var channelUrl: String

}

struct ChannelBox {

    

    var channels: [ChannelModel]

    

    init() {

        let path = NSBundle.mainBundle().pathForResource("channels.plist", ofType: nil)!

        let array = NSArray(contentsOfFile: path)

    

        channels = []

        for dict in array! {

            let channelName = dict["tname"] as! String

            let channelUrl = dict["url"] as! String

            let channelModel = ChannelModel(channelName: channelName, channelUrl: channelUrl)

            channels.append(channelModel)

        }

    }

    

    subscript (index: Int) -> ChannelModel {

        get {

            return channels[index]

        }

    }

}