private function get deWidth():Number
public function set deWidth( w:Number ):void
this.dataProvider.width = w;
.. seems fine, but when using the magic getter you’ll get (heh!) this compiler error “Ambiguous reference to deWidth”.
I’ve found found some blogposts referring to this as a bug. I don’t know if it’s a bug or not, but I know that the cause is that the getter is private and the setter is public - which doesn’t make sense.
So, to fix; either change your setter to private or your getter to public :-)