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:- object(root, % avoid infinite metaclass regression by
instantiates(root)). % making the class its own metaclass
:- 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_/1 value is stored locally, in this class
cv(Value) :-
cv_(Value). % retrive cv_/1 value, shared for all instances
set_cv(Value) :-
retractall(cv_(_)), % retract old cv_/1 value from this class
asserta(cv_(Value)). % assert the new value into this class
:- end_object.
:- object(instance1,
instantiates(root)).
:- end_object.
:- object(instance2,
instantiates(root)).
:- end_object.
:- object(instance3,
instantiates(root)).
:- end_object.
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