Question

I’d like to setf different fields of a struct depending on a certain variable. I decided to use the following approach:

Generate a string with the field’s accessor name:

(setq my-string (format nil "STRUCT-ESTADISTICAS-NUM-~S" x))

and then use intern with funcall:

(funcall (intern my-string) *estadisticas*)

This call returns the correct value of the struct’s field, but if I try setf to modify this value it complains saying:

(setf (funcall(intern my-string) *estadisticas*) 0)
Error: `(SETF FUNCALL)' is not fbound

I can understand why it doesn’t work, but I can’t find a way to modify the struct’s fields.
Any idea?
Thank you.

Answer 1

You want to call a writer function of the struct via its name, and the name of the writer is the list (setf accessor-name); so

(funcall (fdefinition (list 'setf (intern my-string))) 0 estadisticas)

Edit:

Not seeing the rest of your code, it’s hard to fathom what went wrong. On SBCL this works for me:

(defstruct point x y)
(let ((point (make-point :x 1 :y 2)))
  (funcall (fdefinition (list 'setf (intern "POINT-X"))) 10 point)
  point)

The above evaluates to

#S(POINT :X 10 :Y 2),

as expected.