Question

<?php

class Super {
    public $my;
    public function __construct ( $someArg ) {
        if ( class_exists('Sub') ) {    // or some other condition
            return new Sub( $someArg );
        }
        $this->my = $someArg;
    }
}

class Sub extends Super {}

?>

This doesn’t work, as new Super() will be an “empty” Super object (all members are NULL). (PHP doesn’t allow assignments to $this, so $this = new Sub() doesn’t work either).

I know the correct pattern would be a factory here. But that would require a lot of changes in the code, so I’m wondering whether it’s possible to do it this way. Since Sub is-a Super, I don’t see why it shouldn’t be restricted from an OOP point of view.

Answer 1

You can’t assign to $this and you cannot return anything from a constructor.