In Lisp can't make-instance because :name isn't provided

Question

This code creates an error: The slot COMMON-LISP-USER::NAME is unbound in the object #<THING {1002B830F3}>. I tried sbcl and clisp, both creating same problem. I can initialize instance of ash manually, but when done in "when" statement, it doesn't work

(defclass thing ()
  ((name :initarg :name :accessor thing-name)
   (properties :initform nil :accessor thing-properties)))

(defmethod initialize-instance :around ((obj thing) &rest initargs &key &allow-other-keys)
  (let* ((class (class-of obj)))
    (apply #'call-next-method obj
           (loop for (key val) on initargs by #'cddr
                 when (member key '(name properties))  ; Explicitly allow these
                 append (list key val)))))

(defclass process () 
  ((name :initarg :name :accessor process-name)))

(defmethod burn ((proc process) (chair thing) (oxygen thing))
  (declare (ignore proc))
  (when (and (string= (thing-name chair) "chair")
             (string= (thing-name oxygen) "oxygen"))
    (make-instance 'thing :name "ash")))

;; Test
(defparameter *chair* (make-instance 'thing :name "chair"))
(defparameter *oxygen* (make-instance 'thing :name "oxygen"))
(defparameter *burning* (make-instance 'process :name "burning"))

;; Perform the burn operation
(defparameter *result* (burn *burning* *chair* *oxygen*))

;; Debugging output
(format t "Result: ~A" *result*)  ; Should show the created "ash" instance if the burn succeeds

Community · Accepted Answer · 2025-08-06 07:23:01Z

3

The error is inside this method:

(defmethod initialize-instance :around ((obj thing) &rest initargs &key &allow-other-keys)
    (let* ((class (class-of obj)))
    (apply #'call-next-method obj
        (loop for (key val) on initargs by #'cddr
            when (member key '(name properties))  ; Explicitly allow these
                append (list key val)))))

You should use list of keyword symbols, not list of non-keyword symbols: (member key '(:name :properties))

edited Aug 6 at 7:23

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answered Jul 21 at 20:44

Martin Půda

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