Returning a Tuple from a Closure - ios

Question

I'm trying to create an class to retrieve JSON from a web API in Swift. Instead of going with delegates, I thought of using closures but I'm struggling with a few things.
let login = {(email: String, password: String) -> (Int, String) in
let response = { (response: NSHTTPURLResponse!, data: HTTPHandler.Data!, error: NSError!) -> Void in
var value: String? = response.allHeaderFields[HTTPHeaderFields.token] as AnyObject? as? String
var headerData = value?.dataUsingEncoding(NSASCIIStringEncoding)
var values: NSArray = NSJSONSerialization.JSONObjectWithData(headerData, options: .AllowFragments, error: nil) as NSArray
println(values)
return (values[0], values[1]) // Tuple types '(AnyObject!, AnyObject!)' and '()' have a different number of elements (2 vs. 0)
}
let httpHandler = HTTPHandler.POST(SERVER_URL + POSTendpoints.login, data: ["email": email, "password": password], response: response)
return nil // Type '(Int, String)' does not conform to protocol 'NilLiteralConvertible'
}
Here is the closure I wrote. It accepts two parameters (email, password) and should return a tuple (User ID, API Token). I have a separate class called HTTPHandler which calls the server and I get and can parse the response successfully. Here's the example JSON output.
(
2,
JDJ5JDEwJFZ4ZkR4eXlkYUxiYS93TXUwbjBtbnUzaVhidFZBUVVtMTRJM0J3WFFBemszSVVjZ3RWd05h
)
But I can't return the value in a tuple. I get following two errors. I've commented them in the above code snippet where they occur.
I'm still struggling with closure syntax in Swift so I'm not entirely sure if I have done this right. I've defined the closure as a constant. That way can I call this closure from another class? If not, how can I make it possible to do so?
Can someone please help me to resolve these issues?
Thank you.

Answer 1

First of all, in order to return nil you need to make your closure return an optional tuple. Use (Int, String)? or (Int, String)! instead of (Int, String)
You're getting the error "Tuple types '(AnyObject!, AnyObject!)' and '()' have a different number of elements" because you're trying to return a (Int, String) tuple instead of Void which is what the closure returns.
I can't test it myself right now, but it would look something like this:
let login = {(email: String, password: String) -> (Int, String)? in
var returnTuple: (Int, String)? = nil
let response = { (response: NSHTTPURLResponse!, data: HTTPHandler.Data!, error: NSError!) -> Void in
var value: String? = response.allHeaderFields[HTTPHeaderFields.token] as AnyObject? as? String
var headerData = value?.dataUsingEncoding(NSASCIIStringEncoding)
var values: NSArray = NSJSONSerialization.JSONObjectWithData(headerData, options: .AllowFragments, error: nil) as NSArray
println(values)
returnTuple = (values[0], values[1])
}
let httpHandler = HTTPHandler.POST(SERVER_URL + POSTendpoints.login, data: ["email": email, "password": password], response: response)
return returnTuple
}

Answer 2

Regarding the first error, it seems that you should cast values elements to proper types:
return (values[0] as Int, values[1] as String)
Regarding the second error, non-optional type just can't be nil in Swift, if you want to indicate absence of value, you should change return type of your closure to (Int, String)?.