 	/// - returns: a signal producer with no value
 	public func perform(operation: DockerContainerOperation, on inContainers: [DockerContainer]? = nil) -> SignalProducer<(), Rc2Error>
 	{
-		var selectedContainers = containers!
+		var selectedContainers = self.containers!
 		if inContainers != nil {
 			selectedContainers = inContainers!
 		}

			self.imageInfo = newInfo
			self.defaults[.cachedImageInfo] = json
			return true
		}
	}

	/// compares installedImages with imageInfo to see if a pull is necessary

///manages communicating with the local docker engine
public final class DockerManager: NSObject {
	// MARK: - Properties
	/// the containers managed.
	// these should always be referred to as self.containers since many parameters have the name containers
	public fileprivate(set) var containers: [DockerContainer]!
	public var isReady: Bool { return state == .ready }

