'(key: AnyObject, value: AnyObject)' does not have a member named 'subscript'

Question

I have a problem similar to this question, but the answers there isn't helping me.

I have these lines of code:

var id = item["id"] as? String ?? ""
var name = item["name"] as? String ?? ""
var pic = item["pic"] as? String ?? ""

To me these lines of code a pretty much the same. For Xcode, this is a different matter.

The first line is fine. The second two lines generate this error:

'(key: AnyObject, value: AnyObject)' does not have a member named 'subscript'

Here is some more context for you all:

class func getFromJson(json:NSDictionary) -> [Collection] {
    var collections = [Collection]()
    if json.count > 0 {
        for item in json {
            var id = item["id"] as? String ?? ""
            var name = item["name"] as? String ?? ""
            var pic = item["pic"] as? String ?? ""
            var newUser = Collection(id:id, name:name, pic:pic)
            collections.append(newUser)
        }
    }
    return collections
}

Can anyone explain to me how to fix this. Bonus points if you can explain why the first line is fine, but the next two nearly identical lines produce errors!

Thanks in advance.

Answer 1

'(key: AnyObject, value: AnyObject)' indicates that item is not an Dictionary but is a Tuple with a single key/value pair.

Iterating dictionaries in swift interates through tuples:

for (key, value) in json {
    println(key, value)
}

Your for loop indicates that you are probably wanting a json Array of tuples instead of a json Dictionary.

item["id"] would give you a compile time error if you declared the parameter as a tuple. It seems you stumbled onto something hidden with the language with how either tuples or subscripts work under the hood.

More on Subscripts

More on Types (Tuples)