Question

Let’s suppose I have a parent class in PHP like this:

class A {

    private $property;

    public static function factory($arg) {
        $object = new A();
        $object->property = $arg;
        return $object;
    }

}

And I want to extend it in this way:

class B extends A {

    public static function factory() {
        return parent::factory('constant');
    }

}

When I do B::factory() I get a object of type A. What if I want an object of type B? I cannot change anything in the code of class A.

Answer 1

1st version

That’s because you hardcoded the A class in the factory method.
In class A, instead of $object = new A() try (require Php 5.3):

$class_name = get_called_class();
$object = new $class_name;

get_called_class() “Gets the name of the class the static method is called in.”

Shorter version:

$object = new static();

2nd version (hardcoded parent class):

Copy object properties manually:

$parent = parent::factory($args);
$obj = new static();
$obj->setTimestamp($parent->getTimestamp());
$obj->setTimezone($parent->getTimezone());
return $obj;

Or use an hack to do it autoatically:

How to Cast Objects in PHP