extension NSObject {
    
    func addWeakAssociation(object:AnyObject, key: String) {
        
        let getter = { [weak object] in return object }
        
        objc_setAssociatedObject(self, UnsafePointer(bitPattern: key.hashValue), getter, .OBJC_ASSOCIATION_COPY)
        
    }
    
    func getWeakObject(key: String) -> AnyObject? {
        if let getter = objc_getAssociatedObject(self, UnsafePointer(bitPattern: key.hashValue)) as? () -> AnyObject? {
            return getter()
        } else {
            return nil
        }
    }
    
}

func test() {
    let objct = NSObject()
    let weakObject = NSObject()
    objct.addWeakAssociation(object: weakObject, key: "weakObject")
    print(objct.getWeakObject(key: "weakObject"))
    
}