order_new is a class method not a global function.
As the PHP-Manual suggest you can use in this case
usort($data, array($this, "order_new"));
or declare order_new static and use
usort($data, array("myClass", "order_new"));
order_new is a class method not a global function.
As the PHP-Manual suggest you can use in this case
usort($data, array($this, "order_new"));
or declare order_new static and use
usort($data, array("myClass", "order_new"));