SingeltonReadWriteLock.swift

class Singleton {
    // singelton pattern
    private static var privateShared : Singleton?
    
    class func shared() -> Singleton {
        
        // make sure we get an instance from the singleton queue
        guard let uwShared = read(privateShared) else {
            privateShared = Singleton()
            return privateShared!
        }
        return uwShared
    }
    
    func destoy() {
        // make sure we write on the singleton queue and halt reads
        write {
            Singleton.privateShared = nil
        }
    }
    
    private let singletonQueue = dispatch_queue_create("SingletonQueue", DISPATCH_QUEUE_CONCURRENT)
    private static let singletonQueue = dispatch_queue_create("SingletonQueue", DISPATCH_QUEUE_CONCURRENT)
    
    
    
    // attributes
    private var somePrivateAttribute : Int = 0
    var someAttribute : Int {
        get {
            return read(somePrivateAttribute)
        }
        set(value) {
            write {
                self.somePrivateAttribute = value
            }
        }
    }
    
    private init() {
        print("init singleton")
    }
}

// instance read / write
extension Singleton {
    
    private func write(closure:() -> Void) {
        dispatch_barrier_sync(singletonQueue) {
            closure()
        }
    }
    
    private func read<T>(value:T) -> T {
        var returnValue : T = value
        dispatch_sync(singletonQueue) {
            returnValue = value
        }
        return mainQueue(returnValue)
    }
    
    private func mainQueue<T>(value:T) -> T {
        var returnValue : T = value
        dispatch_sync(dispatch_get_main_queue()) {
            returnValue = value
        }
        return returnValue
    }
}

// type read / write
extension Singleton {
    
    private static func write(closure:() -> Void) {
        dispatch_barrier_sync(singletonQueue) {
            closure()
        }
    }
    
    private static func read<T>(value:T) -> T {
        var returnValue : T = value
        dispatch_sync(singletonQueue) {
            returnValue = value
        }
        return mainQueue(returnValue)
    }
    
    private static func mainQueue<T>(value:T) -> T {
        var returnValue : T = value
        dispatch_sync(dispatch_get_main_queue()) {
            returnValue = value
        }
        return returnValue
    }
}

What version of swift is this?