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Java's java.lang.Class class has a getDeclaredFields method which will return all the fields in a given class. Is there something similar for Common Lisp? I came across some helpful functions such as describe, inspect and symbol-plist after reading trying out the instructions in Successful Lisp, Chapter 10 (http://www.psg.com/~dlamkins/sl/chapter10.html). But none of them do what getDeclaredFields does.

Múna
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Bala
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2 Answers2

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You should use class-slots and/or class-direct-slots (both are from CLOS Metaobject Protocol, MOP). class-slots returns all slots that are present in given class, and class-direct-slots returns all slots are declared in class definition.

Different lisp implementations implement MOP slightly differently; use closer-mop package to have uniform interface to MOP.

Example:

(defclass foo ()
  (foo-x))

(finalize-inheritance (find-class 'foo)) ;this is needed to be able to query class slots and other properties. Or, class is automatically finalized when its first instance is created

(class-slots (find-class 'foo))
=> (#<STANDARD-EFFECTIVE-SLOT-DEFINITION FOO-X>)

(slot-definition-name (first (class-slots (find-class 'foo))))
=> FOO-X

Example :

(defun inspect (( object standard-object))
  (inspect-rec (class-slots (class-of object)) object) )


(defun inspect-rec (slots o)
  ( if(atom slots) ()
   (let ((sn (slot-definition-name (car slots)))) (cons (list sn '=> ( slot-value o sn) )  ( inspect-rec (cdr slots) o)))))
Jonas G. Drange
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dmitry_vk
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5

I think you're looking for the MetaObject Protocol for CL.

JP Alioto
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  • This link is giving a 404 error. Please ["Provide context for links"](https://stackoverflow.com/help/how-to-answer); down-voting for now, though there's probably something to this answer, and I know there are other resources for learning about the MOP, as it's sometimes called. Happy to re-consider vote with a fresh link AND a bit more info (perhaps info on something specific that approximates `getDeclaredFields`). – lindes Jan 01 '20 at 22:04