Thanks for your explanation. I do agree with your choice - built-in
performance optimisation over standardised MOP by default.
https://github.com/erikg/ucw-core/blob/master/src/rerl/standard-component/standard-component.lispSearch
for slot-value-using-class and slot-boundp-using-class in this file.
It belongs to UCW library. It works fine in SBCL because SBCL uses 'native'
MOP, and I tried to run it in LispWorks. I do not deny it could be
cl:standard-class. UCW uses its own standard-component-class so the price
mentioned are not used.
Post by Pascal CostanzaHi,
Unfortunately, its not possible to fix this.
In Closer to MOP, I have to balance a couple of requirements, and I cannot
fulfill them all.
In LispWorks, the default protocol for slot accesses is based on symbols,
not on effective slot definition objects. (This is how the CLOS MOP draft
specifications have been defined up until very late in the CLOS MOP
specification process.)
So by default, you say something like (slot-value-using-class (find-class
foo) (make-instance foo) s1), which is understood by LispWorkss CLOS
implementation (or better yet, just the plain (slot-value (make-instance
foo) s1)).
The goal of Closer to MOP is to change the protocols so they are more in
line with what the actual CLOS MOP specification says. In order to be able
to do this, I have to provide two specializations on slot-value-using-class
and friends. The first is a method that still dispatches on slot names that
then calls slot-value-using-class again with the respective effective slot
(cl:defmethod slot-value-using-class
((class standard-class) object (slot symbol))
(declare (optimize (speed 3) (debug 0) (safety 0)
(compilation-speed 0)))
(let ((slotd (find-slot slot class)))
(if slotd
(slot-value-using-class class object slotd)
(slot-missing class object slot 'slot-value))))
Now, I also need to define a method for effective slot definition objects,
which is not provided by default in LispWorks, to make this all work. It
(cl:defmethod slot-value-using-class
((class standard-class) object (slotd
standard-effective-slot-definition))
(declare (optimize (speed 3) (debug 0) (safety 0)
(compilation-speed 0)))
(slot-value-using-class
(load-time-value (class-prototype (find-class 'cl:standard-class)))
object
(slot-definition-name slotd)))
By calling slot-value-using-class again on the slot name, but this time on
the original cl:standard-class instead of Closer to MOPs standard-class, I
now get back the original LispWorks slot access.
I cannot specialize the first method on cl:standard-class. This doesnt
work, because the CLOS MOP specification explicitly requires that each
user-defined method on the standard protocol generic functions must have at
least one argument specialized on ones own class. I dont have a specific
class for the second argument at all, and the third argument must be
specialized on symbol, so what Im left with is to specialize the first
There is no specific specializer available for the second argument, and the
third argument must be standard-effective-slot-definition. (It is
imaginable that the third argument is a subclass of
standard-effective-slot-definition, but that wouldnt solve your issue
either.)
If you think about it, its clear why the requirement of the CLOS MOP
exists: If I were allowed to define methods on standard protocol functions
that are specialized only on standard metaclasses, this would replace the
default behavior of the CLOS implementation, and thus prevent CLOS from
working at all.
One way out would be to force every class to be an instance of
c2cl:standard-class instead of cl:standard-class, as you suggest. However,
I decided against that because this would lead to a potentially severe
performance overhead: CLOS implementations make a major effort to implement
the protocols as efficiently as possible if only standard metaclasses are
involved. However, c2cl:standard-class is not a standard metaclass, so the
CLOS implementation would have to resort to much slower generic
implementations of the protocols. I decided it to be more important that
you get best performance for parts of the protocol that are not specialized
in any way for your own metaclasses, and only have an impact on
subprotocols that you effectively change, as much as possible.
If you subclass c2cl:standard-class, you get the fixed protocols, but if
you dont, you get the default implementation of LispWorks (same for any
other CL implementation, as far as possible).
Yes, this means that you sometimes run into issues like the one you
report. But I believe this is a lower price to pay than trying to get
performance back that you may have lost with a more general implementation.
For your specific problem: Why do you need to call slot-boundp-using-class
manually yourself? This should normally not be required, its normally
better to just call slot-boundp
Pascal
Hi,
CL-USER 1 > (c2cl:defclass foo () ((s1)))
#<STANDARD-CLASS FOO 201010AB>
CL-USER 2 > (c2mop:slot-boundp-using-class (find-class 'foo) (make-instance 'foo) (first (harlequin-common-lisp:class-slots (find-class 'foo))))
Error: The slot #<STANDARD-EFFECTIVE-SLOT-DEFINITION S1 23A4C803> is missing from #<FOO 23A4C2B7> (of class #<STANDARD-CLASS FOO 201010AB>)
The thing is that specialisation defined in
https://github.com/mcna/closer-mop/blob/master/closer-lispworks.lisp uses
standard-class from c2mop, which is later exported, but nothing forces
subsequent code to use it instead of cl:standard-class.
Of course (eq (find-class 'cl:standard-class) (find-class
'c2mop:standard-class)) --> NIL
When I explicitely use c2mop:standard-class however, the specialisation
(c2cl:defclass foo () ((s1)) (:metaclass c2mop:standard-class))
(c2mop:slot-boundp-using-class (find-class 'foo) (make-instance 'foo) (first (harlequin-common-lisp:class-slots (find-class 'foo))))
NIL
As expected. How can it be fixed please? Is there any test suite that can
check what other functionality is affected?
Cheers,
Piotr
--
Pascal Costanza