Hi Leslie,
Elephant does not pay any attention to type information defined as
part of a slot metaobject. The lisp will complain during
deserialization when you try to write the PIC to the changed slot, now
of type STRING. Only OpenMCL, as far as I know, enforces type
checking by default and asserts errors. Allegro and SBCL will quietly
assign the wrong type to the slot, if I recall correctly. Lispworks
will probably complain too.
The right user approach is to provide a function to walk over
instances and update their representation or zero them out. Other
than an assertion on deserialization or a general warning on type
change, I can't think of a really useful default policy.
Have you tried this and seen what happens? What Lisp are you using?
Ian
On Dec 20, 2007, at 10:38 PM, Robert L. Read wrote:
I haven't answered this because I've spent the last three days
trying to get Sean Ross's patch to work; the tests run green with it,
but if you run the tests again they fail.
The easiest way to answer this problem is to try it.
I may have to back out the changes that Sean sent in; they interact
very
badly with the postmodern interface --- or at least the most recent
version of it.
I suspect that I may also be dealing with an SBCL bug of some kind in
the MOP.
I never set out to spend three days on this---the solution always
seemed
to be right around the corner.
On Wed, 2007-12-19 at 10:50 +0100, Leslie P. Polzer wrote:
The user's guide talks about added and discarded slots, but what's
the behaviour
when a slot changes?
Suppose I represent a picture with an object PIC that contains the
location of
a file holding it. I store a bunch of other objects that each have
a picture:
(defpclass myobj ()
((picture :type PIC)))
Now I decide later on that a string would be enough
(defpclass myobj ()
((picture :type STRING)))
What will happen? A bad thing, i.e. a deserialization error?
Is there a way to define how a PIC should be converted to a STRING?
Leslie
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