I often have a class that is composed of a list of another class. For example, I'll have a vector-list class made up of vectors. To avoid writing long statements, I write a method to access the embedded class. However, this method only acts as a getter; I cannot use it to set the slot value. Is there a way to use a method to set a class slot value?
Below is a minimal example:
(defclass vector ()
((name :accessor vector-name
:initarg :name)))
(defclass vector-list ()
((vectors :accessor vector-list-vectors
:initarg :vectors)))
(defun make-vector-list ()
(make-instance 'vector-list
:vectors (list
(make-instance 'vector :name 'v1)
(make-instance 'vector :name 'v2))))
(defmethod access-vector-name ((vt vector-list) vector-idx)
(vector-name (nth vector-idx (vector-list-vectors vt))))
;; returns V1
(print (access-vector-name (make-vector-list) 0))
;; Now, trying to set the same slot returns an error
;; How can I set the slot?
(setf (access-vector-name (make-vector-list) 0) 'new); --> error
The simplest would be to write:
(setf (aref (access-vector-name ...) index) value)`
But if you don't want to expose the fact that you have arrays/vectors, you can define a custom setf expander.
First, only define access-vector-name as a :reader in your class.
Then:
(defun (setf access-vector-name) (newval obj index)
(setf (aref (access-vector-name obj) index) newval))
If the intent is to hide the underlying implementation, maybe access-vector-name is a bad name.