swiftswift3xcode8nstreecontroller

"Ambiguous use of 'children'" when trying to use NSTreeController.arrangedObjects in Swift 3.0

I get an Ambiguous use of 'children' error in XCode 8.0/Swift 3.0 when trying to send a message to the opaque NSTreeController.arrangedObjects object.

Here is a bare playground showing the use case : 

import AppKit

extension NSTreeController {

    func whatever () {
        let k = (self.arrangedObjects as AnyObject).children // error here
    }
}

I try to use AnyObject as a bridge to the underlying ObjC object, which is supposed to be able to get through any method call, I guess.

Xcode signals that it found two candidates that could respond to a "children" message: Foundation.XMLNode and AppKit.NSTreeNode.

Of course the obvious solution (casting to NSTreeNode) is not working because arrangedObjects returns an opaque, proxy object not a real NSTreeNode

Any suggestion on how we're supposed to use NSTreeController.arrangedObjects.children in Swift 3 ?

Solution

  • The two candidates for the children property differ by their type:

    Foundation.XMLNode:137:14: note: found this candidate
    open var children: [XMLNode]? { get }
             ^
AppKit.NSTreeNode:12:14: note: found this candidate
    open var children: [NSTreeNode]? { get }
             ^

    You can resolve the ambiguity by casting the value of the property to the expected type. In your case:

    let k = (self.arrangedObjects as AnyObject).children as [NSTreeNode]?