// ---- previously --------
class Address
{
  public string $name;
  public DateTimeImmutable $birthday;

  public function __construct(string $n, DateTimeImmutable $g)
  {
    $this->name = $n;
    $this->$birthday = $g;
  }
}

// ---- in PHP 8 --------
class Address
{
  public function __construct(
    public string $name,
    public DateTimeImmutable $birthday,
  ) {}
}