How to save an image to photo library (Swift snippet)

This is how I did it in Sigma app with Swift 3.0

    @IBAction func saveToLibrary(_ sender: AnyObject) {
        UIImageWriteToSavedPhotosAlbum(image, self, #selector(image(_:didFinishSavingWithError:contextInfo:)), nil)
    }
    

    func image(_ image: UIImage, didFinishSavingWithError error: NSError?, contextInfo: UnsafeRawPointer) {
        if let error = error {
            // we got back an error!
            let ac = UIAlertController(title: "Save error", message: error.localizedDescription, preferredStyle: .alert)
            ac.addAction(UIAlertAction(title: "OK", style: .default))
            present(ac, animated: true)
        } else {
       
            let ac = UIAlertController(title: "Saved!", message: "The screenshot has been saved to your photos.", preferredStyle: .alert)
            ac.addAction(UIAlertAction(title: "OK", style: .default))
            present(ac, animated: true)
        }
    }