[AS2 - OOP] incrementing properties

Hi everybody

I’m working on a class which extends MC
I would like to be able to do the same as this line: movieclip._width++

I already havewritten the function which modify the status of my MC and works perfectly
But now i want link it to a property, so any variations applied to this property calls the function and modify the MC

How can i do it?

Thanks in advance