class LoginViewController_ByExample: UIViewController {

	private var user = InputUser(email: "", password: "")
	private let userContract = InputUserContract()
	private let formValidator = ModelValidator()

	// MARK: - UITextFieldDelegate

	func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
		let delayed = {
			self.user.email = self.emailField.text ?? ""
			self.user.password = self.passwordField.text ?? ""

			// Validate in 1 line.
			let valid = (try? self.formValidator.validate(self.user, using: self.userContract)) ?? false

			// Update UI.
			// E.g. hide/display Login button based on 'valid' state.
			self.loginButton.isHidden = !valid
		}

		onMainQueue {
			delayed()
		}

		return true
	}
}