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bug#17507: Documentation for `add-text-property' and relatives

From: Eli Barzilay
Subject: bug#17507: Documentation for `add-text-property' and relatives
Date: Thu, 15 Aug 2019 06:41:17 +0300

Um...  Note that I referred *explicitly* to other lisps and schemes.
The assumption that I'm talking about would hold for people who are
used to CL too: a string is indeed more than just a pointer bytes with
a NUL at the end, yet there is no way to change a *property* of "foo"
and end up with #("foo" stuff...).

On Thu, Aug 15, 2019 at 2:57 AM Lars Ingebrigtsen <address@hidden> wrote:
> Eli Barzilay <address@hidden> writes:
> > What I was surprised to find out is that
> >
> >     (let ((s "foo")) (put-text-property 0 3 'foo 'bar s) s)
> >
> > works.  It's probably obvious for elisp hackers, but coming from
> > most other lisps/schemes, I kind of assumed that the #("foo" ...)
> > thing is made of the "foo" string in some vector-like container that
> > holds the properties.  Given that unconscious assumption, I assumed
> > that it wouldn't work, and that I'll need some uglier hack like
> >
> >     (let ((s (propertize "foo" 'foo nil)))
> >       (put-text-property 0 3 'foo 'bar s) s)
> >
> > so that `s' points to an object that can be mutated inside.
> >
> > So I think that it would be a good idea to add a comment in the docs
> > (of all of these functions) that notes that when given a string, they
> > mutate it, and it works even if the input is property-less.  Or just
> > make it easier with showing a example as the above.
> >
> > (Hopefully the above makes sense -- I wonder how many lispers who are
> > not native e-lispers have that assumption...)
> (I'm going through old bug reports that have unfortunately gotten no
> responses yet.)
> Hm...  I think the doc string is pretty clear here:
> ---
> If the optional fifth argument OBJECT is a buffer (or nil, which means
> the current buffer), START and END are buffer positions (integers or
> markers).  If OBJECT is a string, START and END are 0-based indices into it.
> ---
> I understand that if you come from a C background (or something like
> that) your assumption may be that a string is just a bunch of bytes with
> a null at the end, so you can't add any properties to it -- but that's
> not the case in most languages, where a string is an object with lots of
> different qualities in addition to the text itself.
> So I don't think this is something that's desirable to explain in this
> specific context, and I'm closing this bug report.
> --
> (domestic pets only, the antidote for overdose, milk.)
>    bloggy blog: http://lars.ingebrigtsen.no

                   ((x=>x(x))(x=>x(x)))                  Eli Barzilay:
                   http://barzilay.org/                  Maze is Life!

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