|    |      VO      |  DTO |
|----------|:-------------:|------:|
| _Data_ |  yes | yes |
| _Logic_ |    yes   |   no |
| _Identity_ | no |    no |
| _Immutability_ | yes | no |

### VO
```php
final class Address
{
    private $street;
    private $unit;
    private $room;

    public function __construct(string $street, int $unit, ?int $room = null)
    {
        $this->street = $street;
        $this->unit   = $this->handleNumberArgument($unit);
        $this->room   = $room ? $this->handleNumberArgument($room) : null;
    }

    public function assignRoom(int $room): self
    {
        if (null !== $this->room) {
            throw new LogicException('The room is already assigned to this address');
        }

        return new self($this->street, $this->unit, $room);
    }

    public function __toString(): string
    {
        return implode(',', [$this->street, $this->unit, $this->room ?? '']);
    }

    private function handleNumberArgument($value): int
    {
        if ($value <= 0) {
            throw new InvalidArgumentException('Number must be more than \'0\'');
        }

        return $value;
    }
}
```

### DTO

```php
final class UserRegisterRequest
{
    public const PASSWORD_MIN_LENGTH = 6;

    public $username;
    public $password;

    private function __construct(string $username, string $password)
    {
        $this->username = $username;
        $this->assertPasswordLength($password);
        $this->password = $password;
    }

    public static function create(string $username, string $password): self
    {
        return new self($username, $password);
    }

    private function assertPasswordLength(string $password)
    {
        if (self::PASSWORD_MIN_LENGTH >= strlen($password)) {
            throw new InvalidArgumentException('Password must be more than 6 characters.');
        }
    }
}
```