PHP Factory Methods

Question

I read factory methods. Can someone explain why it is suggested that the factory methods be in a separate factory class?

I draw my example from here: http://www.devshed.com/c/a/PHP/Design-Patterns-in-PHP-Factory-Method-and-Abstract-Factory/

class ETF {
  var $data;
  function __construct($data) {
    $this->data = $data;
  }
  function process() {}
  function getResult() {}
}

class VirtualCheck extends ETF {}
class WireTransfer extends ETF {}

class ETFFactory {
  function createETF($data) {
      switch ($data[‘etfType’]) {
      case ETF_VIRTUALCHECK : 
        return new VirtualCheck($data);
      case ETF_WIRETRANSFER :
        return new WireTransfer($data);
      default :
        return new ETF($data);
      }
  }
}

$data = $_POST;
$etf = ETFFactory::createETF($data);
$etf->process();

I would like to write like this:

class ETF {
    final public static function factory($data) {
        switch ($data[‘etfType’]) {
            case ETF_VIRTUALCHECK :
                return new VirtualCheck($data);
            case ETF_WIRETRANSFER :
                return new WireTransfer($data);
            default :
                return new ETF($data);
        }
    }

    var $data;
    function ETF($data) {
        $this->data = $data;
    }
    function process() {}
    function getResult() {}
}

class VirtualCheck extends ETF {}
class WireTransfer extends ETF {}

$data = $_POST;
$etf = ETF::factory($data);
$etf->process();

Am I really wrong about that?

Answer 1

I would not say that you are "mistaken", but there is a "smell". By combining a factory method in an industrial class, the architecture breaks some of SOLID :

• One responsibility: the class now does two things (when it should do it).
• / : ( ).
• : , factory ( ).

, SOLID , . , SOLID , .

, ? , factory , . , , . , :

class ETF {
    final public static factory($kind) {
        switch ($kind) {
        case 'A':
            $etf = static::factoryHelperForA();
            break;
        case 'B':
            $etf = static::factoryHelperForA();
            break;
        }
        return $etf;
    }

    public function apiMethod1() {
        $this->apiMethod1Helper();
    }

    public function apiMethod2() {
        $this->apiMethod2Helper();
    }

    // factory helper
    private static function factoryHelperForA() {
        /* lots of code */
    }

    // another factory helper
    private static function factoryHelperForB() {
        /* lots of code */
    }

    // ugh, now we have api method helpers... totally different responsibility
    private function apiMethod1Helper() {
        /* lots of code */
    }

    // still more...
    private function apiMethod2Helper() {
        /* lots of code */
    }
}

, , , factory , . , SOLID .

, factory EtfFactory.

Answer 2

, Factory Factory.

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Factory . , . , . ( , , , ..). , ( ): ( ), ( , ), , , - . , , Factory.

. - . , , " ". , . , Factory, .

:

• Factory
• Factory