NameValidation.swift

class ViewController: UIViewController {
    @IBOutlet weak var nameTextField: UITextField!
    @IBOutlet weak var passwordTextField: UITextField!
    
    func nameValidation(for field: UITextField) -> Signal<Bool, NoError> {
        return field
            .reactive
            .continuousTextValues
            .skipNil()
            .map { $0.characters.count > 3 }
    }
  
    override func viewDidLoad() {
        super.viewDidLoad()
      
        let validUserNameSignal = nameValidation(for: nameTextField)
        let lastNameFieldSignal = nameValidation(for: lastNameTextField)
        let formValidation =
            SignalProducer(signal: validUserNameSignal.combineLatest(with: lastNameFieldSignal))
                .map { $0 && $1 }
                .prefix(value: false)
        
        formValidation.startWithValues {
                print($0)
        }
    }
}