Extending SplDoublyLinkedList with specific child types and avoiding strict notices

Hopefully the title says it all. Basically I'm extending the SplDoublyLinkedList as it's better on memory than arrays, is object orientated, and it can be extended with additional functionality more easily. It's that last part that is causing some issues. I'm extending to create a list class that only takes specific children. This example will throw PHP strict notices when run, which I ideally want to avoid: <?php class SomeSpecificListClass extends \SplDoublyLinkedList { public class push(SpecificChildTypeClass $item) { parent::push($item); } } Has anyone else tried something like this before and found a better way? Thanks, Ash http://www.ashleysheridan.co.uk