Swift code to use raw Grand Central Dispatch to make requests

SwiftCallbackHell.swift

import Foundation

var todos = [String: Any]()

let dispatchGroup = DispatchGroup()

for todo in 0..10 {
  let url = URL(string: "https://jsonplaceholder.typicode.com/todos/\(todo)")
  dispatchGroup.enter()
  let task = URLSession.shared.dataTask(with: url!) { (data, response, error) in
    let jsonSerialized = try! JSONSerialization.jsonObject(with: data, options: []) as? [String : Any]
    todos += [jsonSerialized]
    // do more stuff
    // ready to end processing on this particular async task?
    dispatchGroup.leave()                                           
  }
  task.resume()
}

dispatchGroup.notify(queue: DispatchQueue.main) {
  print("Got \(todos.count) todos!")
  // other stuff including display on screen
}