func save_to_file(_ textView: UITextView)
    {
        let file = "file.txt"
        let text = textView.text
        if let dir = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first {

            let fileURL = dir.appendingPathComponent(file)

            //writing
            do {
                try text.write(to: fileURL, atomically: false, encoding: .utf8)
            }
            catch {/* error handling here */}
    }