“致命错误:数组索引超出范围swift”

The code being:

代码:

class Singleton {

    class var sharedInstance:Singleton {
        struct Static {
            static var instance:Singleton? = nil
            static var token:dispatch_once_t = 0
        }
        dispatch_once(&Static.token)
            {
                Static.instance = Singleton ()
        }
        return Static.instance!
    }

    var prayerArray = Array<PrayerSound>()

}
class Singleton {