subclassing without sideaffects

12.22: todo.adda/oop/subclassing without sideaffects:
. how does the oop remain secure, and yet reusable?
they are having a lot of fun with subclassing,
so, is there any way to do that safely ?
the general idea is that it creates sideaffects,
so not only do you want to enforce capability limits on apps,
you also want to warn users when an app uses side-affecting features .
. you want to bar cap'grabbing features
like the obj'c categories which allow adding slots to library classes;
however, need to get more aquainted with
why they feel that is needed,
and find some alternative .