Cannot downcast from 'AnyObject' to non-@objc protocol type

The next item I wished to do was to pass in an object to my picker and let it be a choice.  I defined a simple object type of Die, which represents a type of die.

I could not find a way to have interpolation work with the object, for "\(value)", so I decided to have a protocol that can be checked for.

I defined the following protocol:

protocol ProvidesTextValue

{

    var textValue:String { get}

}

With the following usage:

 func pickerView(pickerView: UIPickerView!, titleForRow row: Int, forComponent component: Int) -> String

    {

        let array=getArray(component);

        let value : AnyObject=array[row];

        if value is ProvidesTextValue

        {

            let textProvider=value as ProvidesTextValue

            return "\(textProvider.textValue)"

        }

            return "\(value)";

    }

Which resulted in the error:

DieRollDataSource.swift:61:18: Cannot downcast from 'AnyObject' to non-@objc protocol type 'ProvidesTextValue'

The Swift Programming guide provides the following guidance:

NOTE

You can check for protocol conformance only if your protocol is marked with the @objc attribute, as seen for the HasArea protocol above. This attribute indicates that the protocol should be exposed to Objective-C code and is described in Using Swift with Cocoa and Objective-C. Even if you are not interoperating with Objective-C, you need to mark your protocols with the @objc attribute if you want to be able to check for protocol conformance.

Note also that @objc protocols can be adopted only by classes, and not by structures or enumerations. If you mark your protocol as @objc in order to check for conformance, you will be able to apply that protocol only to class types.

So I had to modify the protocol definition to be:

@objc protocol ProvidesTextValue

{

    var textValue:String { get}

}

This resulted in a runtime error with the very 'useful' error message:
** NSForwarding: warning: object 0x110fa0000 of class '_TtC15SimpleDieRoller3Die' does not implement methodSignatureForSelector: -- trouble ahead

I then modified the class definition with @objc as well, which solved the problem:

@objc class Die : ProvidesTextValue

{

    var dieType:Int

    

    init(die:Int)

    {

        dieType=die;

    }

    var textValue:String { return "\(dieType)" }

}