How to extract a value from function in swift - ios

Question

So I've written a function in swift which gives me a numeric value from JSON api. My question is how can I take the value from function so I can use it in more practical means.
override func viewDidLoad() {
super.viewDidLoad()
getJSON()
}
func getJSON(){
let url = NSURL(string: baseURL)
let request = NSURLRequest(URL: url!)
let session = NSURLSession(configuration: NSURLSessionConfiguration.defaultSessionConfiguration())
let task = session.dataTaskWithRequest(request) { (data, response, error) -> Void in
if error == nil{
let swiftyJSON = JSON(data: data!)
let usdPrice = swiftyJSON["bpi"]["USD"]["rate"].doubleValue
print(usdPrice)
}else{
print("There was an error!")
}
let usdPrice gets me the value so how can I take that from the function getJSON() and do something with it, for example attribute it to some label in Main.storyboard

Answer 1

Unfortunately the other answers are incorrect. Just returning a value will not work because you are getting the value from the completion closure of dataTaskWithRequest.
Having the statement return usdPrice should be a compiler error because the completion closure does not have a return value.
You'll need to add your own completion closure to getJSON that gets the double as a parameter.
override func viewDidLoad() {
super.viewDidLoad()
getJSON { (usdPrice) -> Void in
// do something with usdPrice
print(usdPrice)
}
}
func getJSON(completion: (Double) -> Void) {
let url = NSURL(string: baseURL)
let request = NSURLRequest(URL: url!)
let session = NSURLSession(configuration: NSURLSessionConfiguration.defaultSessionConfiguration())
let task = session.dataTaskWithRequest(request) { (data, response, error) -> Void in
if error == nil{
let swiftyJSON = JSON(data: data!)
let usdPrice = swiftyJSON["bpi"]["USD"]["rate"].doubleValue
completion(usdPrice)
} else {
print("There was an error!")
}
}

Answer 2

Your function needs to return the value as a result of its execution. For more details check out this: https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Functions.html#//apple_ref/doc/uid/TP40014097-CH10-ID160

Answer 3

You have to have a return value for the function. The code below should work.
func getJSON() -> Double {
let url = NSURL(string: baseURL)
let request = NSURLRequest(URL: url!)
let session = NSURLSession(configuration: NSURLSessionConfiguration.defaultSessionConfiguration())
var usdReturnValue : Double = 0.0
let task = session.dataTaskWithRequest(request) { (data, response, error) -> Void in
if error == nil{
let swiftyJSON = JSON(data: data!)
let usdPrice = swiftyJSON["bpi"]["USD"]["rate"].doubleValue
print(usdPrice)
usdReturnValue = usdPrice
}else{
print("There was an error!")
}
}
return usdReturnValue
}