Re: goops - accessors, methods and generics

[Stefan Israelsson Tampe <stefan.itampe@gmail.com>]

I don't find the behavior strange.

1. Declaring dialog generic in mg-1 and mg-2 and merge generics in
mg-3 solves the mg-3 case.

2. When exporting dialog in mg-4 the system automatically undefine the
dialog symbol imported. By in stead using :re-export (dialog) the mg-4 
case
is solved.

The question if we should automatically always merge generics and
automatically always define accessors generic I do not agree. The
reason is that the current approach is more general. On the other hand
as we saw subtle bugs can appear and a good warning/diagnosing system
that can help pinpoint these issues would indeed be a good additions.

/Stefan

On Thursday, February 21, 2013 07:51:39 PM David Pirotte wrote:
> Hello all,
> 
> given the following 4 modules, I am facing what I consider an
> inconsistent goops behavior and have one problem which leads to my
> recurrent request of goops default behavior should be to [a] always
> create a generic function for accessors and methods that do not [yet]
> have one, visible in the entire guile space [all modules] and [b] the
> default behavior should be '(merge-generics replace warn-override-core
> warn last) [but that at least that one I can set using :duplicate, I
> know]
> 
> so, 2 or 3 things to show what happens and see what developers think.
> 
> 
> 1]
> 
> if i use in the repl or in my init.scm
> 
>   (default-duplicate-binding-handler '(merge-generics replace
> warn-override-core warn last))
> 
> ->
> 
> 	david@capac:~/gnu/kise 14 $ guile
> 	GNU Guile 2.0.7.9-21982
> 	...
> 	scheme@(guile-user)> (default-duplicate-binding-handler
> '(merge-generics replace warn-override-core warn last))
> scheme@(guile-user)> (use-modules (mg-3))
> 	(mg3/letstry)
> 
> 	;;; note: source file /usr/alto/projects/gnu/tests/mg-3.scm
> 	;;;       newer than compiled
> /home/david/.cache/guile/ccache/2.0-LE-8-2.0/usr/alto/projects/gnu/te
> sts/mg-3.scm.go ;;; note: auto-compilation is enabled, set
> GUILE_AUTO_COMPILE=0 ;;;       or pass the --no-auto-compile argument
> to disable. ;;; compiling /usr/alto/projects/gnu/tests/mg-3.scm
> 	WARNING: (mg-3): `dialog' imported from both (mg-1) and (mg-2)
> 	;;; compiled
> /home/david/.cache/guile/ccache/2.0-LE-8-2.0/usr/alto/projects/gnu/te
> sts/mg-3.scm.go WARNING: (mg-3): `dialog' imported from both (mg-1)
> and (mg-2) ERROR: In procedure scm-error:
> 	ERROR: No applicable method for #<<accessor> dialog (1)> in call
> (dialog #<<widget-a> 1e97660>)
> 
> 
> 2]
> 
> if I uncomment the :duplicates block in mg-3, then it's fine
> 
> 	... ...
> 	;;; ("widget-a:" dialog-a)
> 
> 	;;; ("widget-b:" dialog-b)
>         scheme@(guile-user)>
> 
> 
> 3]
> 
> what is more of a problem with the existing goops default, for me, is
> expressed in the mg-4.scm 'case': i can not make it work unless I
> manually create another module, manually making generics and make sure
> it is loaded before ... or rename the accessors, which both solutions
> are really against my expectation and [long] CLOS practice: why
> should I have to manually do things which are inherent to oop [same
> name for slots pertaining to different classes is so common that i
> can not see any large application not having to do so, for semantic
> reasons].
> 
> unless i did miss that there is a way to ask goops to create a generic
> fucntion for accessors and methods per default ?
> 
> 
> scheme@(guile-user)> (use-modules (mg-4))
> ;;; note: source file /usr/alto/projects/gnu/tests/mg-4.scm
> ;;;       newer than compiled
> /home/david/.cache/guile/ccache/2.0-LE-8-2.0/usr/alto/projects/gnu/te
> sts/mg-4.scm.go ;;; note: auto-compilation is enabled, set
> GUILE_AUTO_COMPILE=0 ;;;       or pass the --no-auto-compile argument
> to disable. ;;; compiling /usr/alto/projects/gnu/tests/mg-4.scm
> ;;; compiled
> /home/david/.cache/guile/ccache/2.0-LE-8-2.0/usr/alto/projects/gnu/te
> sts/mg-4.scm.go scheme@(guile-user)> (mg4/letstry)
> ERROR: In procedure scm-error:
> ERROR: No applicable method for #<<accessor> dialog (1)> in call
> (dialog #<<widget-a> 23b7a60>)
> 
> 
> 
> ;; cheers
> cheers :)
> David
> 
> 
> 
> ;;mg-1.scm
> 
> (define-module (mg-1)
> 
>   :use-module (oop goops)
>   :
>   :export (<widget-a>
> 
> 	    dialog
> 	    make-widget-a))
> 
> (define-class <widget-a> ()
>   (dialog #:accessor dialog #:init-keyword #:dialog #:init-value #f))
> 
> (define (make-widget-a)
>   (make <widget-a> #:dialog 'dialog-a))
> 
> 
> ;; mg-2.scm
> 
> (define-module (mg-2)
> 
>   :use-module (oop goops)
>   :
>   :export (<widget-b>
> 
> 	    dialog
> 	    make-widget-b))
> 
> 
> (define-class <widget-b> ()
>   (dialog #:accessor dialog #:init-keyword #:dialog #:init-value #f))
> 
> (define (make-widget-b)
>   (make <widget-b> #:dialog 'dialog-b))
> 
> 
> ;; mg3.scm
> 
> (define-module (mg-3)
> 
>   :use-module (oop goops)
>   :
>   :use-module (mg-1)
>   :use-module (mg-2)
> 
>   #!
> 
>   :duplicates (merge-generics
> 
> 	       replace
> 	       warn-override-core
> 	       warn
> 	       last)
>   !#
> 
>   :export (mg3/letstry))
> 
> (define (mg3/letstry)
>   (pk "widget-a:" (dialog (make-widget-a)))
>   (pk "widget-b:" (dialog (make-widget-b)))
>   (values))
> 
> 
> ;; mg-4.scm
> 
> (define-module (mg-4)
> 
>   :use-module (oop goops)
>   :use-module (mg-1)
>   :
>   :duplicates (merge-generics
> 
> 	       replace
> 	       warn-override-core
> 	       warn
> 	       last)
> 
>   :export (<widget-b>
> 
> 	    dialog
> 	    make-widget-b
> 	    mg4/letstry))
> 
> (define-class <widget-b> ()
>   (dialog #:accessor dialog #:init-keyword #:dialog #:init-value #f))
> 
> (define (make-widget-b)
>   (make <widget-b> #:dialog 'dialog-b))
> 
> (define (mg4/letstry)
>   (pk "widget-a:" (dialog (make-widget-a)))
>   (pk "widget-b:" (dialog (make-widget-b))))