:- object(root,
instantiates(root)).
:- private(cv_/1).
:- dynamic(cv_/1).
:- mode(cv_(?integer), zero_or_one).
:- public(cv/1).
:- mode(cv(?integer), zero_or_one).
:- public(set_cv/1).
:- mode(set_cv(+integer), one).
cv_(0). % cv value is stored locally, in this class
cv(Value) :-
cv_(Value). % retrive cv value, shared for all instances
set_cv(Value) :-
retractall(cv_(_)), % retract old cv value from this class
asserta(cv_(Value)). % assert the new value in this class
:- end_object.
