On Sat, Aug 2, 2014 at 7:38 AM, Pascal Costanza pc@p-cos.net wrote:
On 2 Aug 2014, at 06:35, Jean-Claude Beaudoin < jean.claude.beaudoin@gmail.com> wrote:
I think I found the subsection you refer to: AMOP 5.3.1 (pp. 142-144)
"Implementation and User Specialization", which contains two sub-subsections with titles starting with "Restrictions on".
I will try to decipher those and their implications now that I have
renewed motivation to do so.
There are similar restrictions defined in http://www.lispworks.com/documentation/HyperSpec/Body/11_abab.htm - bullet 19.
I missed that one too. Thank you for pointing it out.
But after modifying my test code to take account of it I saw no difference in the results. It turns out that it is the last bullet of the sub-subsection "Restrictions on Portable Programs" that is the key factor in the issue I am interested in here (last bullet of page 144 in AMOP, or here http://franz.com/support/documentation/current/doc/mop/concepts.html#portable as pointed by Steve). It basically states that the defmethod on slot-value-using-class must happen before any call to make-instance on a class the method uses as a specializer. (And then goes on to motivate this definition order restriction). If I modify my test code to comply with this rule (see slot_mop_strict.lsp here attached) then sbcl stops being the odd man out and behaves like clisp and ACL (which I think is the proper behavior).
Further, if I agree to stop tickling the system where it does not like to be tickled and define a class tracked_class as a subclass of standard-class to be used as a metaclass of the classes I want to track (see slot_mop_strict_tracked_class.lsp here attached), then all of sbcl, clisp, ccl and ACL show the same behavior, properly calling slot-value-using-class both from slot-value or from the slot accessor. Only LispWorks persists in its (erroneous, I think) behavior of calling s-v-u-c only from slot-value. I think there is a consensus emerging here.
Thank you all for your help on this matter with a special emphasis toward Steve.