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classvars

This folder contains an example that shows how to implement class variables as defined in Smalltalk. The name shared instance variables is however much more accurate. In systems like Logtalk, which enables the use of explicit metaclasses, true class variables are just the class (as an object) own instance variables!

This example defines a root class, root and three instances, instance1, instance2, and instance3. The root class defines a shared instance variable (using a dynamic predicate) and the setter and getter methods which implement the variable sharing behavior.

Print Logtalk, Prolog backend, and kernel versions (if running as a notebook):

%versions

Start by loading the example:

logtalk_load(classvars(loader)).

Get the value of the class variable for each instance:

instance1::cv(Value1), instance2::cv(Value2), instance3::cv(Value3).

Change the value of the class variable via instance1:

instance1::set_cv(1).

Get the value of the class variable for the other instances:

instance2::cv(Value2), instance3::cv(Value3).