//单例方法1

class SingleTonOne{

    static var sharedInstanceOne:SingleTonOne{

     struct SingleTonStruct {

     static var onceToken:dispatch_once_t = 0

     static var staticInstanceOne:SingleTonOne? = nil

    }

    dispatch_once(&SingleTonStruct.onceToken) {

            SingleTonStruct.staticInstanceOne = SingleTonOne()

        }

        return SingleTonStruct.staticInstanceOne!

    }

}

//单例方法2

class SingleTonTwo{

    class var sharedInstanceTwo:SingleTonTwo{

        struct StaticStruct {

            static let staticInstanceTwo:SingleTonTwo = SingleTonTwo()

        }

        return StaticStruct.staticInstanceTwo

    }

}

//单例方法3

class SingleTonThree{

    class var sharedInstance:SingleTonThree{

        return sharedInstanceThree

    }

}

private let sharedInstanceThree = SingleTonThree()

//单例方法4

class SingleTonFour{

   static let sharedInstanceFour = SingleTonFour()

    private init(){}

}