How do you copy a PHP object into a different object type

Question

1. New class is a subclass of the original object

2. It needs to be php4 compatible

Answer 1

You could have your classes instantiated empty and then loaded by any number of methods. One of these methods could accept an instance of the parent class as an argument, and then copy its data from there

class childClass extends parentClass
{
    function childClass()
    {
        //do nothing
    }

    function loadFromParentObj( $parentObj )
    {
        $this->a = $parentObj->a;
        $this->b = $parentObj->b;
        $this->c = $parentObj->c;
    }
};

$myParent = new parentClass();
$myChild = new childClass();
$myChild->loadFromParentObj( $myParent );