ToLeftSegueUnwind.swift

import UIKit

class ToLeftSegueUnwind: UIStoryboardSegue {

  override func perform() {

    let sourceView = self.source.view as UIView!
    let destinationView = self.destination.view as UIView!

    let screenWidth = UIScreen.main.bounds.size.width

    let window = UIApplication.shared.keyWindow
    window?.insertSubview(destinationView!, aboveSubview: sourceView!)

    UIView.animate(withDuration: 0.2, animations: { () -> Void in
      destinationView?.frame = (destinationView?.frame.offsetBy(dx: -screenWidth, dy: 0.0))!
      sourceView?.frame = (sourceView?.frame.offsetBy(dx: -screenWidth, dy: 0.0))!
      }, completion: { (_) -> Void in
        self.source.dismiss(animated: false, completion: nil)
    })
  }
}