🚀 go-pugleaf

Another approach to what are increasingly being called "per-class slots":


   --  set up a metaclass for such classes with this altered inheritance;
	for sake of discussion, call it PER-CLASS-SHARED-SLOTS-CLASS

   --  place a method on ENSURE-CLASS-USING-CLASS specialized to this
	metaclass (i.e. PER-CLASS-SHARED-SLOTS-CLASS) which snoops at
	the :direct-superclasses argument to collect the names of all
	the shared slots from all the supers which are of metaclass
	PER-CLASS-SHARED-SLOTS-CLASS.  Then alter the :direct-slots
	argument to add canonicalized slot specifications for such
	shared slots (see CANONICALIZE-DIRECT-SLOT, which is also
	from AMOP), and then just CALL-NEXT-METHOD.

The trick here is to utilize all the pre-existing machinery of an
implementation's support for shared slots, but to fake-out the 
interface between DEFCLASS and the actual class creation protocol
to make it look like every DEFCLASS form for the new metaclass actually
had a :ALLOCATION :CLASS specification for any inherited shared slot.

So here we are using the metaobject protocol to alter the inheritance
behaviour within an (extended) metaclass.


Refinement:  figure out how to put the method on MAKE-INSTANCE, or
on INITIALIZE-INSTANCE, instead of on ENSURE-CLASS-USING-CLASS.

More refinement: figure out how to collate all the actual direct slot
specifications from the set of all superclasses so as to resolve  _each 
and every potential slot specification_  item in the automatically
generated slot spec list.




-- JonL --