Инициализация свойств (полей) в классе

class Test
{
  public $var1;
  public $var2
  public function __construct($var1, $var2)
  {
    this->var1 = $var1;
    this->var2 = $var2;
  }
}
 
$test = new Test(1,2);

$db = new DataBase($host, $user, $pass);
$obj = new UserMapper($db);
 
$oUser = $obj->getUserById(1);
$oUser = $obj->getUserByPhone('96212345678');
 
class UserMapper {
    protected $db;
 
    public function __construct($db) {
        $this->db = $db;
    }
 
    public function getUserById($user_id) {
        return $this->db->select("select * from users where user_id = $user_id");
    }
 
    public function getUserByPhone($phone) {
        return $this->db->select("select * from users where phone = $phone");
    }
}

$obj = new UserMapper();
$oUser = $obj->getUserById($host, $user, $pass, 1);
$oUser = $obj->getUserByPhone($host, $user, $pass, '96212345678');
 
class UserMapper {
    public function getUserById($host, $user, $pass, $user_id) {
        $db = new DataBase($host, $user, $pass);
        return $db->select("select * from users where user_id = $user_id");
    }
 
    public function getUserByPhone($host, $user, $pass, $phone) {
        $db = new DataBase($host, $user, $pass);
        return $db->select("select * from users where phone = $phone");
    }
}