Cacher is the code snippet organizer for pro developers

func underline() {
    let yourAttributes : [String: Any] = [
        NSFontAttributeName : self.titleLabel!.font,
        NSForegroundColorAttributeName : self.titleLabel!.textColor,
        NSUnderlineStyleAttributeName : NSUnderlineStyle.styleSingle.rawValue]
        
    let attributeString = NSMutableAttributedString(string: self.title(for: .normal)!,
                                                    attributes: yourAttributes)
    self.setAttributedTitle(attributeString, for: .normal)
}