Re: Should redefining a class reinitialize shared slots?

[Danny Bobrow <Bobrow.pa@Xerox.COM>]

    It seems to me the only predictable rules are: (1) all
    class slots retain their values when the class is redefined. (2)
    all class slots are reinitialized when the class is redefined.

    I prefer rule 1 because it is analogous to the rule for
    instance slots. Also, it's easier to reinitialize a slot that was
    retained than to retain a slot that was reinitialized, if a user
    wants to implement behavior different from the default.

Despite the fact that I think I would usually want to retain current
values of class slots, I worry about a confusion of models for the user.
Rule 2 is a pure text based model; Rule 1 is a semi-structural model.
This leads to questions about what changes in a class slot cause it to
get reinitialized?

If I change the :type 
If I change the :initform 
If I change its order in the list of slots  
If I add another class slot before it in the list
If I change its name  

If one were doing structural editing, then none of these would cause
reinitialization (even a name change).  When dealing with the defclass
form as text, the answer is less clear -- even with respect to the name
change i.e.  consider changing to "all-instances" from
"all-my-instances" or from "allinstances".

    I prefer rule 1 because it is analogous to the rule for
    instance slots. Also, it's easier to reinitialize a slot that was
    retained than to retain a slot that was reinitialized, if a user
    wants to implement behavior different from the default.
I find these arguments strong, but still find rule 2 is most consistent.
Rule 1 probably is desirable in most cases, but I think will be
confusing when we consider the above cases -- again, shades of DWIM.  My
intuition is not strong on this, so I would like to see opinions from
Gregor and Patrick (others too, of course).

    I prefer rule 1 because it is analogous to the rule for
    instance slots. Also, it's easier to reinitialize a slot that was
    retained than to retain a slot that was reinitialized, if a user
    wants to implement behavior different from the default.
  

RPG writes:
    There is a third option, which would be to specify the
    redefinition initialization action in the DEFCLASS as a class slot
    option (:retain or :reinitialize, for example).
I don't think additional language features are useful here; in
particular, I would hate to see options specified that depended on the
value(s) of other option(s).  I think we must make up our mind what
model to be supported.