[comp.lang.clos] Adding new mixins to a predefined class

alanr@chopin.media-lab.media.mit.edu (Alan Ruttenberg) (06/18/91)

Is is possible to incrementally modify the definition of a class?

What I have in mind is something like

(defclass extra-mixin () ((extra-instance-variable)))

(add-class-mixin predefined-class extra-mixin)

- actually it would make more sense to do something like a setf of
class-precedence-list, since you don't know where to add the mixin above.

The example comes up in the following way. There is a class of windows
which is supplied by the implementation. I want to add some
functionality which requires an extra instance variable. I can't
modify the source code, because I don't have it. So it would be nice
to modify the class by adding a new instance variable, or some new
default-initargs, or whatever.

-alan