GNU bug report logs - #76017
31.0.50; Which args can cl-nintersection and cl-nset-difference mutate?

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Message #33 received at 76017 <at> debbugs.gnu.org (full text, mbox):

From: Pip Cet <pipcet <at> protonmail.com>
To: "Basil L. Contovounesios" <basil <at> contovou.net>
Cc: Mattias Engdegård <mattias.engdegard <at> gmail.com>,
 Stefan Monnier <monnier <at> iro.umontreal.ca>, 76017 <at> debbugs.gnu.org
Subject: Re: bug#76017: 31.0.50;
 Which args can cl-nintersection and cl-nset-difference mutate?
Date: Fri, 14 Feb 2025 15:21:09 +0000

"Basil L. Contovounesios" <basil <at> contovou.net> writes:

> Pip Cet [2025-02-14 11:13 +0000] wrote:
>
>> Maybe if feature/igc is merged, and becomes a common option, we can
>> formally make cl-nintersection an alias of cl-intersection,
>
> I haven't followed most of the feature/igc developments; how do they
> affect the choice of whether cl-nintersection aliases cl-intersection?

My hope is that an efficient GC greatly reduces the need for destructive
operations, but I'm not sure whether that's more of a dream :-)

>> As a followup, I would like to propose removing claims of cons cells
>> being reused "whenever possible", though: we reserve the right to
>> mutate one of the arguments, but we don't, so we shouldn't make such
>> claims.  (And what's "whenever possible" supposed to mean, anyway?  All
>> cons cells are equal!)
>
> The right to mutate one of the arguments is the function's raison
> d'être, and its users ought to be made aware of that before they choose
> to use it.  Today the implementation suffers from a clear performance
> bug, but tomorrow that might be fixed, and at such time its already
> informed users will automatically benefit from the fix.

That sounds like a good way to fix it, "simply" adjust the function to
do what the docstring already claims it does!

Good luck!

Pip

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