Trouble constructing usable Swift array using NSSet

Question

I am working with Swift, using a dictionary, and then trying to put info into an array, and access values in the array. This is what I have in my code:

// I have abbreviated the actual dictionary to not waste question space...
var plateIssuers: Dictionary<String,String> = [
    "Alberta": "Canada",
    "British Columbia": "Canada",
    "Manitoba":"Canada",
    "VERMONT":"USA",
    "WASHINGTON":"USA",
    "WISCONSIN":"USA",
    "WEST VIRGINIA":"USA",
    "WYOMING]":"USA"]

// This is an attempt that seems to work to create an Array of unique values (turning into sets and then back to array
let countries:Array = NSSet(array: Array<String>(plateIssuers.values)).allObjects
let issuers:Array = NSSet(array: Array<String>(plateIssuers.keys)).allObjects

Later, in a tableView function, I have the following code:

println(countries[1])
cell.textLabel.text = countries[(indexPath.row)]

The println works fine (prints "Canada"), but the cell.textLabel line gives the following error (won't build):

Could not find an overload for 'subscript' that accepts the supplied arguments

How can the println work but not the next line. I should also mention that the second line works if I just refer to an array I built in a simple manner with strings in it. Is my problem the way I created the "countries" array? or is it a problem in how I am referencing it? Thanks

Thanks, but that's how I had it originally. I put them in to see if it would help, which it didn't. — Narwhal
– Narwhal, Commented Jul 6, 2014 at 23:46
The problem is that you are typing countries too loosely. You must type it as Array<String>: in particular, you must cast the result of allObjects to Array<String>. Every type in Swift must be extremely specific, and things are not magically downcast for you as they come across the bridge from Objective-C. — matt
– matt, Commented Jul 6, 2014 at 23:48

matt · Accepted Answer · 2014-07-06 23:56:38Z

3

Do this:

let countries = NSSet(array: Array<String>(plateIssuers.values)).allObjects as Array<String>

Swift's compiler as usual is being coy in its expression of the problem. What it means here is that subscripting an array of AnyObject, which is what comes back from allObjects, is possible, but is not going to net you a String, which is what a label's text property expects.

answered Jul 6, 2014 at 23:56

matt

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1 Comment

matt Over a year ago

And I suggest you file a bug about the inadequacy of the compiler error. In general Swift's way of saying "you are not passing on the right side the type that the left side expects" is extremely obscure and generally points the user in the wrong directly entirely.

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