class substitution in php -

is there way make work? see example :

class car {         function __construct($type){                 switch ($type) {                         case 'big' : return new big_car();                         case 'small' : return new small_car();                 }         }         function whatisit () {                 echo "this car ;( \n";         } }  class big_car extends car {         function __construct(){}         function whatisit () {                 echo "this big car ;) \n";         } }  class small_car extends car {         function __construct(){}         function whatisit () {                 echo "this small car ;) \n";         } } 

so goal use way:

$mycar = new car('big'); $mycar->whatisit(); // want it's big 

i guess bad way , cannot work way maybe there trick?

ps:: know can use special static method but...

you need car factory create new cars; not javascript :)

class car_factory  {     function create_car($type = null)      {         switch ($type) {              case 'big':                  return new big_car();               case 'small':                  return new small_car();               case null:                  return new car();         }         throw new invalidargumentexception($type);     } }  $factory = new car_factory; $small_car = $factory->create_car('small'); $std_car = $factory->create_car(); 

of course, should remove __construct function original code.

as mentioned in comments generalize using dynamic classes, assuming class extensions have same constructor , class naming consistent:

class car_factory {     function create_car($type = null)     {         if (is_null($type)) {             return new car();         }          $class = "{$type}_car";         if (class_exists($class)) {             $obj = new $class();              if ($obj instanceof car) {                 return $obj;             }         }          throw new invalidargumentexception($type);     } } 

personally have no preferences either way; if extensibility key factor, go it, otherwise stick simple switch.