Re: Is it possible to remove a slot when inheriting?

On May 15, 8:16 pm, Joe Marshall <eval.ap...@xxxxxxxxx> wrote:
On May 15, 7:24 am, Pedro Kroger <pedro.kro...@xxxxxxxxx> wrote:



Hi,

suppose I have a class with 6 slots, is it possible to inherit that
class except for one slot? for instance, if I have foo like this:

(defclass foo ()
(a1 a2 a3 a5 a5 a6))

and bar is a subclass of foo:

(defclass bar (foo)
...)

foo will have, of course, the 6 slots, but I want bar to have all
slots of foo except a6. I don't have any specific use for this, I'm
just thinking if this is possible or not. (I don't even know if this
is good practice)

This is an instance of `subtractive inheritance'. CLOS doesn't
support it by default (but you can always change that).

It's probably not a good idea because if BAR inherits from FOO, then a
BAR object should be usable as a FOO. If the BAR object doesn't have
an a6 slot, then it is likely to not work for certain methods.

Consider a rectangle inheriting from polygon. You want to keep a list
of points in polygon, but you want width/height, x/y slots in
rectangle. You define an accessor method `points` that computes the
list of points for rectangles.

Jules

.

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