A protocol that indirectly implements another protocol more than once

Question

I am doing some test projects to learn Swift, and there is a compilation problem that I cannot solve.

I defined a protocol like this:

@objc protocol MyDataProvider : UICollectionViewDataSource, UICollectionViewDelegate, NSObjectProtocol {
    var myData : AnyObject { get }
}

and the class implementing it:

class MyData : NSObject, MyDataProvider {
    var myData:AnyObject

    init() {
        self.myData = Int()
    }

    func collectionView(collectionView: UICollectionView!, numberOfItemsInSection section: Int) -> Int {
        return 1
    }

    func collectionView(collectionView: UICollectionView!, cellForItemAtIndexPath indexPath: NSIndexPath!) -> UICollectionViewCell! {
        return nil
    }
}

I can create an instance of this class and refer to it through a protocol variable:

let dataProvider : MyDataProvider = MyData()

Next, I want to use this instance in the view controller:

class MyController : UIViewController {
    let dataProvider : MyDataProvider = MyData()

    @IBOutlet var collectionView : UICollectionView

    override func viewDidLoad() {
        super.viewDidLoad()

        self.collectionView.dataSource = dataProvider
        self.collectionView.delegate = dataProvider
    }
}

The last 2 assignments are reported by the compiler as errors, with the following error message:

Type 'MyDataProvider' does not conform to protocol 'NSObjectProtocol'

If I do not use the interface and declare the property as a class type:

let dataProvider = MyDate()

it compiles. So there MyDataProvidershould be something wrong with the protocol , I just can’t understand that.

If I delete one of the two delegates implemented by the interface, after commenting the corresponding line into viewDidLoad()compilation, it still fails. But if I remove NSObjectProtocolfrom the protocol:

protocol MyDataProvider : UICollectionViewDelegate {
    var myData : AnyObject { get }
}

compilation now succeeds. So, it UICollectionViewDelegateimplements NSObjectProtocol, therefore, it seems that the protocol cannot implement another protocol more than once, directly or indirectly. But if I remove NSObjectProtocolfrom the interface and leave two delegates to view the collection:

protocol MyDataProvider : UICollectionViewDataSource, UICollectionViewDelegate {
    var myData : AnyObject { get }
}

Compilation

still not running because both implement NSObjectProtocol. How to solve this?

Answer 1

It seems like this was fixed in beta 3. So, I think it was a bug. I was about to file a radar, but in the end they were faster than me :)