Swift dynamically cast nil to optional

Question

The following code works:

nil as! String?
"muffin" as! String?

Therefore I also expect this to work:

var magicArray: [Any?] = ["Muffin", nil, 3]

class Box<T> {

    var index: Int

    init(index: Int){
        self.index = index
    }

    func get() -> T {
        return magicArray[index] as! T //crash
    }

}

But neither

let box = Box<String?>(index: 0)
box.get()

nor

let box = Box<String?>(index: 1)
box.get()

works as expected. The program crashes at the cast in get(). This however works:

let box = Box<Int>(index: 2)
box.get()

I need to be able to cast a Any? value to T inside my class where T can be any type, including optionals. The Any? actually comes from an array of Any? so there is no other way of verifying it’s of the correct type T.

Is this possible?

Answer 1

If you need a generic wrapper, this should work for you:

final class Wrapper<T> {
    final let wrappedValue: T
    init(theValue: T) {
        wrappedValue = theValue
    }
}

You can replace let with var to make it mutable.

Edit:

This is the code I used to test it on a playground.

var s : Any?

s = "some string"

let w = Wrapper(theValue: s)

w.wrappedValue

let int = 3

let w2 = Wrapper(theValue: int)

w2.wrappedValue

w2.wrappedValue = 3

let array : [Any?] = [s, int, nil, "abc", NSObject()]

for obj in array {
    let wrapper = Wrapper(theValue: obj)
}