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From: Drew Adams <drew.adams@oracle.com>
To: Michael Heerdegen <michael_heerdegen@web.de>
Cc: Eric Abrahamsen <eric@ericabrahamsen.net>, 34708@debbugs.gnu.org
Subject: bug#34708: alist-get has unclear documentation
Date: Tue, 12 Mar 2019 07:53:13 -0700 (PDT)	[thread overview]
Message-ID: <bbb57527-e6df-424b-9943-e0c74e31b62a@default> (raw)
In-Reply-To: <87a7i01bk0.fsf@web.de>

> > > (progn
> > >   (setq my-alist '((a . 1) (b . 2)))
> > >   (push (car my-alist) my-alist)
> > >   ;; my-alist ==> (#1=(a . 1) #1# (b . 2))
> > >   (setf (alist-get 'a my-alist nil 'remove) nil))
> > >   ;; my-alist ==> ((b . 2))
> > >
> > > This is because the code uses delq to delete a found cons, and delq
> > > removes all `eq' elements.
> > >
> > > Is it worth to document or change that?
> >
> > Sounds like an implementation/design artifact.  If that will stay as
> > part of the design then yes, I'd say such behavior needs to be
> > documented.
> 
> BTW with a different viewpoint, when you use
>  (setcdr (assoc 'a my-alist) 17)
> 
> on the above degenerated alist you also change _both_ of the 'a
> associations, so one could argue that the `alist-get' setter behaves
> correctly when removing both: there are not two 'a associations in
> MY-ALIST but the same one has just been added two times, so it's correct
> to remove both of them.

OK.  Put it differently: it's worth documenting
that updating an alist entry with `setf' is a
"destructive" operation: it can change list
structure.  Dunno whether that is already said
somewhere, but even if it is, a reminder wouldn't
hurt.





  reply	other threads:[~2019-03-12 14:53 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-02  4:50 bug#34708: alist-get has unclear documentation Miguel V. S. Frasson
2019-03-02  9:25 ` Michael Heerdegen
2019-03-02 15:40   ` Miguel V. S. Frasson
2019-03-02 18:10     ` Michael Heerdegen
2019-03-02 19:06       ` Eric Abrahamsen
2019-03-03  0:15         ` Phil Sainty
2019-03-03 12:50           ` Michael Heerdegen
2019-03-19  1:35             ` Michael Heerdegen
2019-03-02 19:51       ` Miguel V. S. Frasson
2019-03-02 20:32         ` Eric Abrahamsen
2019-03-03 11:32       ` Miguel V. S. Frasson
2019-03-03 12:21         ` Michael Heerdegen
2019-03-03 15:51           ` Drew Adams
2019-03-03 16:49             ` Eric Abrahamsen
2019-03-04 16:24             ` Eric Abrahamsen
2019-03-04 16:38               ` Michael Heerdegen
2019-03-04 17:16                 ` Eric Abrahamsen
2019-03-04 18:22                   ` Michael Heerdegen
2019-03-04 22:49                     ` Eric Abrahamsen
2019-03-05 12:35                       ` Michael Heerdegen
2019-03-05 22:50                         ` Eric Abrahamsen
2019-03-06  0:16                           ` Drew Adams
2019-03-11 13:39                             ` Michael Heerdegen
2019-03-11 14:52                               ` Drew Adams
2019-03-11 16:19                                 ` Michael Heerdegen
2019-03-11 17:48                                   ` Drew Adams
2019-03-12 13:04                                     ` Michael Heerdegen
2019-03-12 14:48                                       ` Drew Adams
2019-03-12 16:08                                         ` Michael Heerdegen
2019-03-12 16:48                                           ` Drew Adams
2019-03-12 17:45                                             ` Michael Heerdegen
2019-03-12 13:12                                 ` Michael Heerdegen
2019-03-12 14:53                                   ` Drew Adams [this message]
2019-03-12 15:38                                     ` Michael Heerdegen
2019-03-12 16:18                                       ` Drew Adams
2019-03-12 17:55                                         ` Michael Heerdegen
2019-03-15 15:54                                           ` Michael Heerdegen
2019-03-15 18:48                                             ` Eric Abrahamsen
2019-03-27 22:31                                               ` Michael Heerdegen
2019-04-19  1:33                                                 ` Michael Heerdegen
2019-04-19  2:24 ` bug#34708: Thanks Miguel V. S. Frasson
2019-04-19  4:18   ` Michael Heerdegen

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