Issue: DEFSTRUCT-REDEFINITION (version 1)

[masinter.pa@Xerox.COM]

Perhaps we can bring a new version of this issue with us for distribution
at the January meeting.

I think the problem is that defstruct accessors are often compiled with
"knowledge" of the structure, in a way that defclass accessors are not. I
think of "defstruct" as "the most efficient defclass", i.e., I'd like to
leave maximum room for optimization. However, error-if-redefined seems a
bit too strong, e.g., if all I do is change the initial value, it doesn't
old compiled accessors or even old instances.

 
     ----- Begin Forwarded Messages -----

Date: Wed, 7 Dec 88 19:56 PST
 From: Gregor.pa
Subject: Re: [masinter.pa: [cl-cleanup@sail.stanford.edu: DRAFT Issue:
DEFSTRUCT-REDEFINITION (Version 1)]]
To: masinter.pa
Fcc: BD:>Gregor>mail>outgoing-mail-4.text.newest
In-Reply-To: The message of 7 Dec 88 15:40 PST from masinter.pa
Message-ID: <19881208035629.7.GREGOR@PORTNOY.parc.xerox.com>
Line-fold: no

Sorry, but I just don't have the time to write this up just now.  I am
barely managing to do what I have to do.  Chapter 3 can support either
of the proposals.  As I have written it now, I believe it specifies
error-if-redefined.

The only point about the relation to chapter 3 is that chapter 3 gives a
technical language for defining it.  There are really three options:

error-if-redefined

error-iff-instances-exist

error-iff-used

In CLOS terminology these are:

(defmethod reinitialize-instance ((c structure-class) &rest ignore)
  (error "..."))

or

(defmethod reinitialize-instance ((c structure-class) &rest ignore)
  (when (class-finalized-p c)
    (error "...")))

or

"The results are undefined if an instance with metaclass structure-class
is accessed after the generic function make-instances-obsolete has been
called with that class as an argument."
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