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The function add_parameter() adds a parameter to an object. Once
you have created a parameter on an object, the methods on that object
can use it to refer to a variable on that object or any of its
descendents, using the C-- constructs described in
Variables.
Two objects can have parameters of the same name; a third object which inherits from both of them will contain two separate variables for those parameters. Methods on the first object will refer to one variable, and methods on the second object will refer to the other. Likewise, variables on separate objects are distinct, even though the methods which can access them and the parameter used by the method are the same.
Note that this system does not permit children to access the variables used by their ancestors directly. Objects can build on the abstractions of their parent objects, but not their internal representations.