libera/commonlisp - IRC Chatlog

22:55:05 ecomcon Should I be creating subclasses solely to discriminate between methods?

22:55:22 pjb ecomcon: if you need to.

22:55:39 pjb ecomcon: can you ask a concrete question?

22:58:21 TMA in my experience, the answer to this type of technical question is either really obvious to the asker as soon as they ask it; in the remaining cases the answer is usually "no, try thinking more"

22:59:09 ecomcon pjb: sure. In a graphical application, I have a BINARY-PARTITION class with two fields, PRIMARY and SECONDARY, that point to each subdivision. I've subclassed BINARY-PARTITION into VERTICAL-PARTITION and HORIZONTAL-PARTITION, which have no fields, for the purpose of implementing separate DRAW and PICK methods.

23:00:32 pjb If you didn't have subclasses, you'd have to add an ORIENTATION slot, and in the single method, test for it. It's better in terms of OOP, to define the subclasses, indeed, to define specific methods for them.

23:01:20 ecomcon At first, BINARY-PARTITION had an ORIENTATION field, which told DRAW how to behave, but I thought that was essentially the logic of multiple dispatch, so I turned them into subclasses

23:01:24 pjb ecomcon: notice that in CL we also have CHANGE-CLASS, so you can change the orientation easily.

23:01:38 pjb ecomcon: seems good.

23:06:32 ecomcon oh, right, "slot," not "field." I come from java. don't tell anyone.