Used for http://blog.gitter.im/2016/02/10/how-to-cache-view-controllers-in-ios/

MasterViewController.swift

class MasterViewController: UITableViewController {

  let cache = NSCache()

  override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
    if let indexPath = tableView.indexPathForSelectedRow {
      let object = objects[indexPath.row] as! NSDate
      let controller = cache.objectForKey(object) as? DetailViewController ?? (storyboard?.instantiateViewControllerWithIdentifier("DetailViewController"))! as! DetailViewController
      cache.setObject(controller, forKey: object)
      controller.detailItem = object
      controller.navigationItem.leftBarButtonItem = self.splitViewController?.displayModeButtonItem()
      controller.navigationItem.leftItemsSupplementBackButton = true

      navigationController!.popToRootViewControllerAnimated(false)
      navigationController!.pushViewController(controller, animated: true)
    }
  }

  ...

}