From: Pip Cet <pipcet@gmail.com>
To: Stefan Monnier <monnier@iro.umontreal.ca>
Cc: "Basil L. Contovounesios" <contovob@tcd.ie>,
Paul Eggert <eggert@cs.ucla.edu>,
Drew Adams <drew.adams@oracle.com>,
emacs-devel@gnu.org
Subject: Re: master f51f963: Fix some side-effecting uses of make-text-button
Date: Sun, 07 Jun 2020 09:31:58 +0000 [thread overview]
Message-ID: <878sgzxlv5.fsf@gmail.com> (raw)
In-Reply-To: <jwvpnabq2hy.fsf-monnier+emacs@gnu.org> (Stefan Monnier's message of "Sat, 06 Jun 2020 18:14:29 -0400")
Stefan Monnier <monnier@iro.umontreal.ca> writes:
>> If I expect a function to look at a string argument, but it actually
>> modifies its argument, that's equally confusing.
>
> I hate mutability, yes. But mutability of literals amounts to
> self-modifying code, which is yet a bit more evil.
And, just once in a while, so very useful :-)
You're right, though, mutability of literals is a more serious concern
than mutability in general.
>> If I modify data that's been used in a hash key, that's even more
>> confusing. If I modify data in an image spec in a Lisp callback from
>> the image backend, Emacs will crash. These cases deserve being
>> thought about, too.
>
> We agree, but I'm not sure what it is you're suggesting we should do.
Mostly: don't make it harder to experiment with mutability by pretending
we already have anything like it.
> We obviously can't make existing data types unilaterally immutable since
> it would break way too much code. Are you suggesting we add new
> constructors for "immutable cons", "immutable string", ...?
> Or a `set-immutable` function?
Not at this point, no. I can describe the code I'm playing with, but
it's quite different and I'm not sure it's worth the considerable
performance cost...
>> The cost of this isn't negligible; the single bit which I expect will be
>> kept for every string, cons cell, or vector isn't that significant, but
>> so far what's been proposed would be complicated to implement, explain,
>> and use.
>
> I'm not exactly sure what has been suggested, to be honest.
> Are you referring to the idea of making literal strings immutable?
> I'm not sure what is the implementation plan for such a thing.
> It seems at least not completely straightforward.
I think the issue has been resolved: if I understand correctly, Paul is
probably going to propose an actual patch which makes strings immutable,
and we can discuss it then.
>> It would lead to some people developing a false sense of security and
>> others becoming insecure and copying everything needlessly (and
>> dangerously, for cyclic objects). And it would effectively prevent any
>> competing system of mutability, I fear.
>
> That makes me think there's been a fairly concrete proposal that has
> been made and which I missed (since otherwise, it seems unclear how
> you'd get to these conclusions). Can someone point me to it?
You're right, we should wait for such a proposal.
next prev parent reply other threads:[~2020-06-07 9:31 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200604223056.17078.81265@vcs0.savannah.gnu.org>
[not found] ` <20200604223058.1850020A26@vcs0.savannah.gnu.org>
2020-06-04 22:44 ` master f51f963: Fix some side-effecting uses of make-text-button Stefan Monnier
2020-06-05 0:58 ` Paul Eggert
2020-06-05 9:27 ` Pip Cet
2020-06-05 10:51 ` Basil L. Contovounesios
2020-06-05 12:46 ` Pip Cet
2020-06-05 13:51 ` Basil L. Contovounesios
2020-06-05 14:31 ` Pip Cet
2020-06-05 15:48 ` Basil L. Contovounesios
2020-06-05 18:17 ` Paul Eggert
2020-06-06 8:18 ` Pip Cet
2020-06-06 16:57 ` Drew Adams
2020-06-06 17:57 ` Stefan Monnier
2020-06-06 19:00 ` Pip Cet
2020-06-06 19:49 ` Paul Eggert
2020-06-06 20:23 ` Drew Adams
2020-06-07 9:14 ` Pip Cet
2020-06-06 22:14 ` Stefan Monnier
2020-06-07 1:40 ` Paul Eggert
2020-06-07 15:24 ` Stefan Monnier
2020-06-07 23:42 ` Paul Eggert
2020-06-07 9:31 ` Pip Cet [this message]
2020-06-06 20:19 ` Drew Adams
2020-06-06 17:54 ` Paul Eggert
2020-06-06 19:41 ` Pip Cet
2020-06-06 20:15 ` Paul Eggert
2020-06-07 9:21 ` Pip Cet
2020-06-07 23:37 ` Paul Eggert
2020-06-06 20:11 ` Drew Adams
2020-06-06 22:16 ` Stefan Monnier
2020-06-06 23:27 ` Drew Adams
2020-06-05 13:02 ` Stefan Monnier
2020-06-05 13:50 ` Basil L. Contovounesios
2020-06-06 19:09 ` Paul Eggert
2020-06-06 20:19 ` Drew Adams
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