AnyType error in Swift array

Question

Trying to make and shuffle a card deck in Swift, made up of Card objects in an array called cardDeck. Then I want to shuffle it. Relevant code:

    var cardDeck = [card]()

    for ind in 1 ... 4  
    {
        for ind2 in 1 ... 13
        {
            cardDeck.append(card(number: ind2, color: ind))
        }
    }

    cardDeck = GKRandomSource.sharedRandom().arrayByShufflingObjectsInArray(cardDeck)

"Cannot assign value of type [anyobject] to logic.card" ("logic" is the overall class name, and Card is another class within it)

Anyone know whats wrong? I guess the array is not an AnyObject type of array since I declared it as containing cards, right?

Answer 1

The problem is that arrayByShufflingObjectsInArray takes an [AnyObject] and returns an [AnyObject].

Therefore its going to completely throw away your [Card] type information that you provide as an input, and thus give you an error about not being able to convert types when you try to assign the output back to your original array. I suspect this is due to the method being implemented in Objective-C, not Swift.

A more Swifty version of the method would look like this:

func arrayByShufflingObjectsInArray<T:AnyObject>(array:[T]) -> [T] {
    ...
}

Through using generics, you can preserve the type information that you pass in to begin with, returning the same type that you inputted. In fact, you can write your own extension of GKRandomSource in order to do just that:

extension GKRandomSource {
    func arrayOfSameTypeByShufflingObjectsInArray<T:AnyObject>(array:[T]) -> [T] {
        return arrayByShufflingObjectsInArray(array) as! [T]
    }
}

^{(Feel free to come up with a more catchy name for the method)}

The force downcast is used as an ugly solution to the problem – which is why I recommend creating an extension, rather than using this directly. It cannot crash, as the output array is guaranteed to contain objects of the same type as the input (as the array you pass in can only contain a single type).

You can now use it like so:

cardDeck = GKRandomSource.sharedRandom().arrayOfSameTypeByShufflingObjectsInArray(cardDeck)