Re: Class redefinition and class-changed.

[Patrick H Dussud <DUSSUD%Jenner%ti-csl.csnet@RELAY.CS.NET>]

     I don't like Patrick's particular proposal, though.
     GET-OBSOLETE-CLASSES-FOR-REDEFINITION is too complicated, because it
     returns a whole alist rather than being just the primitive.  In addition, I
     don't think the set of "classes implicated in the class-redefinition of
     CLASS" is computable until the details of the redefinition are known.
     Suppose
       (defclass one () (a b))
       (defclass two (one) (c))
       (defclass three (one) (d))
     Now suppose we redefine one as follows:
       (defclass one () (a b d))
     Referring to the third paragraph on page 1-11 of 87-002, one and two are
     "implicated", but three is not, or at least, whether three is implicated is
     implementation-dependent.  But if the new slot had been named e, both two
     and three would have been implicated.  I don't think the information in
     Patrick's alist is needed anyway; when defining a method, one only defines
     it for the obsolete class corresponding to one class.  If a different
     method needs to be defined for an obsolete subclass, the function can be
     called again.

I see.  I don't care that much about the alist as long as we can get the
obsolete class of "one".

     
     Thus I would replace Patrick's proposal with GET-OBSOLETE-CLASS-FOR-REDEFINITION
     which takes one argument, a class, and returns one value, the obsolete class
     that is a copy of the current definition of the class and will be used the next 
     time the class is redefined; this is created the first time you ask for it.
     Perhaps GET-OBSOLETE-CLASS-FOR-NEXT-REDEFINITION would be a better name.

     As Danny proposed, a primitive to get the obsolete classes corresponding to
     redefinitions that have already taken place is useful, for instance in case
     you didn't realize ahead of time that you would need a CLASS-CHANGED method
     and now want to patch up the program.  I would suggest a function
     GET-OBSOLETE-CLASSES-FOR-PAST-REDEFINITIONS which takes one argument, a
     class, and returns one value, a list of obsolete classes, newest first.
Sounds OK.

I'll have to think some more about the rest of the message. Our
connection with Arpanet was broken and we got it back just one
hour ago.     

Patrick.