CommonLisp Function for dynamically looking up bindings in packages - package

Question

Is there a way to dynamically ask for bindings in another package, and by dynamically i mean by not knowing the exact name of a binding in some package. A concrete case would be:
As in package B, i know there exists a package A which has a certain class and i extract all direct slots of that class by (in LispWorks):
(setq direct-slots (mapcar #'slot-definition-name
(class-direct-slots (class-of class-in-package-A))))
Now i want to bind those slots to some values using MAPCAR:
(mapcar #'(lambda (slot) (list slot
(funcall slot class-in-package-A)))
direct-slots)
This doesn't work since i am in package B and need package precision for the call to (funcall slot class-in-package-A), packageA::slot is obviously wrong. Is there a function for this which searchs for a certain symbol in a package?

Answer 1

If you have a slot-name and want to get the value of the named slot in some object, use slot-value:
(mapcar (lambda (slot-name)
(slot-value some-object slot-name))
slot-names)
Slot names are symbols, and they will not magically lose their package if you happen to “be” in a different package. I think your confusion is that you are thinking about accessors, but those are a different thing (they use something like slot-value internally).
CL-USER> (defpackage #:foo
(:use #:cl))
#<PACKAGE "FOO">
CL-USER> (defpackage #:bar
(:use #:cl #:sb-mop)) ; in SBCL
#<PACKAGE "BAR">
CL-USER> (in-package #:foo)
#<PACKAGE "FOO">
FOO> (defclass afoo ()
((a :initarg :a)
(b :initarg :b)))
#<STANDARD-CLASS FOO::AFOO>
FOO> (in-package #:bar)
#<PACKAGE "BAR">
BAR> (mapcar #'slot-definition-name
(class-direct-slots (find-class 'foo::afoo)))
(FOO::A FOO::B)
BAR> (let ((slot-names (mapcar #'slot-definition-name
(class-direct-slots (find-class 'foo::afoo))))
(obj (make-instance 'foo::afoo
:a 1
:b 2)))
(mapcar (lambda (slot-name)
(slot-value obj slot-name))
slot-names))
(1 2)
In general, you should be using accessors in “user” code, and you should know which accessors exist for a given object. It also shouldn't matter for user code whether something is a direct slot.