Why do duplicate elements in a SwiftUI array cause a warning?

For a word game, I am using .map to create an array of the letters of a guessed word, for example:

var guessWordArray = "BALANCE".map{String($0)}

which creates the array

["B", "A", "L", "A", "N", "C", "E"]

but then I get the warning,

"...the ID A occurs multiple times within the collection, this will give undefined results."

I don't understand why an array with duplicate elements would "give undefined results." Is this an improper use of an array? Is there an alternative I should use?

I would expect an array not to 'care' what elements are in it and whether they are all the same, different, or any mix. I am obviously missing something.

Solution

The warning message is quite explicit. Looking at the documentation about ForEach, this component needs a unique ID to distinguish the elements that are passed in. In this scenario, you're passing string itself by \.self.

["B", "A", "L", "A", "N", "C", "E"]

You can see "A" character appears twice within the array, that's why the warning occurs.

As @workingdog mentioned above, you need to create a model that fully conforms to Identifiable, something like:

struct CharacterElement: Identifiable {
    var id = UUID()
    var value: String
}

After that, you're able to remove \.self within ForEach:

var words = "BALANCE".map { CharacterElement(value: String($0)) }

var body: some View {
    ForEach(words) {
        //TODO:
    }
}