cartId() public method

public cartId ( ) : string
return string
 /**
  * @param ChangeBillingAddress $command
  * @throws InvalidArgumentException
  */
 public function handle(ChangeBillingAddress $command)
 {
     $billing = new Address($command->name(), $command->street(), $command->postCode(), $command->city(), $command->countryIso2Code());
     $checkout = $this->checkouts->getForCart(new CartId($command->cartId()));
     $checkout->changeBillingAddress($billing);
 }