[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Is it safe to modify a property list directly with PLIST-PUT?
From: |
Teemu Likonen |
Subject: |
Re: Is it safe to modify a property list directly with PLIST-PUT? |
Date: |
Mon, 27 Jul 2009 08:59:18 +0300 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/23.1.50 (gnu/linux) |
On 2009-07-26 22:07 (+0200), Pascal J. Bourguignon wrote:
> Teemu Likonen <tlikonen@iki.fi> writes:
>> (setq my-data '((:foo "one" :bar "two")
>> (:foo "three" :bar "four")))
>
> It is never safe to modify literal data!
Oh yes, that was a stupid example. MY-DATA is not really created that
way. We can assume this:
> (setq my-data (list (list :foo "one" :bar "two")
> (list :foo "three" :bar "four")))
> Notice also that like delete, plist-put returns the result, it cannot
> always modify the property list in place. So you have to restore the
> result:
>
> (setf (nth 1 my-data) (plist-put (nth 1 my-data) :bar "New value"))
Thanks. Now, let's go one step further while still assuming that we are
not using Emacs CL extension (perhaps just for my education). Is this
reliable:
(let ((item (nth 1 my-data)))
(setq item (plist-put item :bar "New value")))
At least it seems to be working: the change appears in MY-DATA too:
((:foo "one" :bar "two")
(:foo "three" :bar "New value"))