Appending a variable outside the scope of a function in Swift 3 - swift

Question

I am trying to append jsonFile, however, I am not able to append jsonFile with a new NSString unless I use a mutuable variable for the parameter file in the function. I have found the solution of using "inout" but in this case I get the error of "scaping closures can only capture inout parameters explicitly by value file.append(jsonData)
var jsonFile: [NSString] = []
func function(file: inout [NSString]){
let request = NSMutableURLRequest(url: URL(string: "https://parse.udacity.com/parse/classes/StudentLocation?limit=1")!)
request.addValue("QrX47CA9cyuGewLdsL7o5Eb8iug6Em8ye0dnAbIr", forHTTPHeaderField: "X-Parse-Application-Id")
request.addValue("QuWThTdiRmTux3YaDseUSEpUKo7aBYM737yKd4gY", forHTTPHeaderField: "X-Parse-REST-API-Key")
let session = URLSession.shared
let task = session.dataTask(with: request as URLRequest) { data, response, error in
if error != nil { // Handle error...
return
}
let jsonData = NSString(data: data!, encoding: String.Encoding.utf8.rawValue)!
print(NSString(data: data!, encoding: String.Encoding.utf8.rawValue)!)
file.append(jsonData)
}
task.resume()
}
function(file: &jsonFile)
print(jsonFile)

Answer 1

You are dealing with asynchronous code. You should not use an inout parameter. Instead, you should be using a completion handler.
Something like the following will work:
var jsonFile: [String] = []
func function(completion: #escaping (String?) -> Void) {
var request = URLRequest(url: URL(string: "https://parse.udacity.com/parse/classes/StudentLocation?limit=1")!)
request.addValue("QrX47CA9cyuGewLdsL7o5Eb8iug6Em8ye0dnAbIr", forHTTPHeaderField: "X-Parse-Application-Id")
request.addValue("QuWThTdiRmTux3YaDseUSEpUKo7aBYM737yKd4gY", forHTTPHeaderField: "X-Parse-REST-API-Key")
let session = URLSession.shared
let task = session.dataTask(with: request) { data, response, error in
if let data = data, error != nil {
if let jsonData = String(data: data, encoding: .utf8) {
completion(jsonData)
} else {
completion(nil)
}
} else {
completion(nil)
}
}
task.resume()
}
function() { (string) in
if let string = string {
jsonFile.append(string)
}
print(jsonFile)
}
Note all of the other clean up. Don't use NSString, use String. Don't use NSMutableURLRequest, use URLRequest with var.