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bug#20423: goops - inheritance of slot options

From: David Pirotte
Subject: bug#20423: goops - inheritance of slot options
Date: Fri, 24 Apr 2015 23:05:38 -0300


        GNU Guile
        goops - inheritance of slot options
        severity - serious

The current goops implementation breaks the [clos] protocol [*] for inheritance 
slot options.  This is a serious bug.

Below, [A] what stklos does, [B] what goops does, [*] a summary of what the clos
protocol says wrt  inheritance of slot options.


[A]     Here is what stklos does:


--8<---------------cut here---------------start------------->8---
(define-class <person> ()
  ((name :accessor name :init-keyword :name :init-form "")
   (age :accessor age :init-keyword :age :init-form -1)))

(define-class <teacher> (<person>)
  ((subject :accessor subject :init-keyword :subject :init-form "")))

(define-class <maths-teacher> (<teacher>)
  ((subject :init-form "Mathematics")))
--8<---------------cut here---------------end-------------->8---

address@hidden:~/alto/projects/stklos 15 $ stklos
*   STklos version 1.10
 *  Copyright (C) 1999-2011 Erick Gallesio - Universite de Nice <address@hidden>
* * [Linux-3.16.0-4-amd64-x86_64/pthread/readline/utf8]
stklos> (load "subclass-slot-redefinition.scm")
stklos> (define p2 (make <maths-teacher> :name 'john :age 34))
;; p2
stklos> (describe p2)
#[<maths-teacher> 28a2420] is an an instance of class <maths-teacher>.
Slots are: 
     age = 34
     name = john
     subject = "Mathematics"
stklos> (subject p2)

[B]     Here is what goops does:


--8<---------------cut here---------------start------------->8---
(use-modules (oop goops))

(define-class <person> ()
  (name #:accessor name #:init-keyword #:name #:init-form "")
  (age #:accessor age #:init-keyword #:age #:init-form -1))

(define-class <teacher> (<person>)
  (subject #:accessor subject #:init-keyword #:subject #:init-form ""))

(define-class <maths-teacher> (<teacher>)
  (subject #:init-form "Mathematics"))
--8<---------------cut here---------------end-------------->8---

address@hidden:~/alto/projects/guile-tests/goops 51 $ guile
GNU Guile
Copyright (C) 1995-2014 Free Software Foundation, Inc.

Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'.
This program is free software, and you are welcome to redistribute it
under certain conditions; type `,show c' for details.

Enter `,help' for help.
scheme@(guile-user)> (load "subclass-slot-redefinition.scm")
;;; note: auto-compilation is enabled, set GUILE_AUTO_COMPILE=0
;;;       or pass the --no-auto-compile argument to disable.
;;; compiling 
scheme@(guile-user)> (define p2 (make <maths-teacher> #:name 'john #:age 34))
scheme@(guile-user)> ,use (oop goops describe) scheme@(guile-user)> (describe 
#<<maths-teacher> 1432300> is an instance of class <maths-teacher>
Slots are: 
     name = john
     age = 34
     subject = "Mathematics"
scheme@(guile-user)> (subject p2)
ERROR: In procedure scm-error:
ERROR: No applicable method for #<<accessor> subject (1)> in call (subject
#<<maths-teacher> 1432300>)

Entering a new prompt.  Type `,bt' for a backtrace or `,q' to continue.
scheme@(guile-user) [1]> 

[*] A summary of what the clos protocol says:

        [ this is a copy/paste from a clos tutorial, also pointed by
        [ the Stklos reference manual:

        [       http://www.aiai.ed.ac.uk/~jeff/clos-guide.html#slots

        When there are superclasses, a subclass can specify a slot that has 
        been specified for a superclass. When this happens, the information in 
        options has to be combined. For the slot options listed above, either 
        option in the subclass overrides the one in the superclass or there is a

           :ACCESSOR  -  union
           :INITARG   -  union
           :INITFORM  -  overrides

        This is what you should expect. The subclass can change the default 
        value by overriding the :initform, and can add to the initargs and 

        However, the union for :accessor is just a consequence of how generic
        functions work. If they can apply to instances of a class C, they can 
        apply to instances of subclasses of C. (Accessor functions are generic.)

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