             self.images[aKey] = nil
         }
 
-        dispatch_async(_queue, block)
+        dispatch_async(_set_queue, block)
     }
 }
 

    }
    let directory = Directory()

    private let _queue = dispatch_queue_create("swift.imageloader.queues.diskcached", DISPATCH_QUEUE_SERIAL)
}

// MARK: accessor


extension Diskcached: ImageCache {

    subscript (aKey: NSURL) -> UIImage? {

        get {
            var value : UIImage?
            dispatch_sync(_subscript_queue) {
                value = self.objectForKey(aKey)
            }

