NSManagedObject Can't conform to protocol in Swift

This worked for me. Try it for yourself and see if it works:

class MyEntity: NSManagedObject {

    @NSManaged var testAttribute: String
}

@objc
protocol MyProtocol {

    var testAttribute: String { get set }
}

extension MyEntity: MyProtocol { }

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        let appDelegate = UIApplication.sharedApplication().delegate as AppDelegate
        let myContext = appDelegate.managedObjectContext!
        let entity: MyEntity = NSEntityDescription.insertNewObjectForEntityForName("MyEntity", inManagedObjectContext: myContext) as MyEntity
        foo(entity)
        println(entity.testAttribute)
    }

    func foo(var object: MyProtocol) {
        object.testAttribute = "bar"
    }
}

The below also worked, but I think the above is a better way to do it:

@objc
protocol MyProtocol {

    var testAttribute: String { get set }
}

class MyEntity: NSManagedObject, MyProtocol {

    @NSManaged var testAttribute: String
}

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        let appDelegate = UIApplication.sharedApplication().delegate as AppDelegate
        let myContext = appDelegate.managedObjectContext!
        let entity: MyEntity = NSEntityDescription.insertNewObjectForEntityForName("MyEntity", inManagedObjectContext: myContext) as MyEntity
        foo(entity)
        println(entity.testAttribute)
    }

    func foo(var object: MyProtocol) {
        object.testAttribute = "bar"
    }
}