php agreggating objects , need explanation -

i have example provided book :

class address {     protected $city;      public function setcity($city) {         $this -> city = $city;     }      public function getcity() {         return $this -> city;     } }  class person {     protected $name;     protected $address;      public function __construct() {         $this -> address = new address;     }      public function setname($name) {         $this -> name = $name;     }      public function getname() {         return $this -> name;     }      public function __call($method, $arguments) {         if (method_exists($this -> address, $method)) {             return call_user_func_array(                     array($this -> address, $method), $arguments);         }     } } $rasmus=new person;         $rasmus->setname('rasmus lerdorf');         $rasmus->setcity('sunnyvale');         print $rasmus->getname().' lives in '.$rasmus->getcity().'.'; 

however have problem understanding code.

how use __construct agreggate object , why need __call function?

__construct constructor person class , instantiates each person object.

__call allows setcity method called on object of type person. class person not possess method named setcity, using __call, passes method call $address instance variable of type address. address class contains actual definition of setcity.

both php magic functions: http://php.net/manual/en/language.oop5.magic.php