OOP Learning Mode

Consider the following script. What will it output?

$global_obj = null;
class my_class
{
     var $value;
     function __construct()
     {
         global $global_obj;
         $global_obj = &$this;
     }
}

$a = new my_class;
$a->value = 5;

$global_obj->value = 10;
echo $a->value;