GNU bug report logs - #56199
hash table equality predicate [PATCH]

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Mattias Engdegård <mattiase <at> acm.org>
Subject: bug#56199: closed (Re: bug#56199: hash table equality predicate
 [PATCH])
Date: Sat, 25 Jun 2022 16:57:02 +0000

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Your bug report

#56199: hash table equality predicate [PATCH]

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 56199 <at> debbugs.gnu.org.

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56199: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=56199
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Mattias Engdegård <mattiase <at> acm.org>
To: Lars Ingebrigtsen <larsi <at> gnus.org>
Cc: 56199-done <at> debbugs.gnu.org
Subject: Re: bug#56199: hash table equality predicate [PATCH]
Date: Sat, 25 Jun 2022 18:56:27 +0200

24 juni 2022 kl. 20.21 skrev Lars Ingebrigtsen <larsi <at> gnus.org>:

> I can't ever recall wanting to compare two hash tables for equality
> (like, that's not what you use a hash table for)

No, you're right -- it's better to wait until there is a concrete need for it.

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From: Mattias Engdegård <mattiase <at> acm.org>
To: bug-gnu-emacs <at> gnu.org
Subject: hash table equality predicate [PATCH]
Date: Fri, 24 Jun 2022 19:19:54 +0200

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Recently[1] a predicate for structural equality was requested that also recurses through hash tables.
It showed that Emacs doesn't even come with a way of comparing hash tables. Third-party implementations exist but if the code quoted in [2] is representative, perhaps it would make sense to add a `hash-table-equal-p` predicate?
Even implemented entirely in Lisp it would be an order of magnitude faster (and actually correct).

The attached code is not without flaws but provides a rough starting point.
(This is not meant as a strong argument for or against adding it in the first place.)

[hash-table-equal-p.diff (application/octet-stream, attachment)]

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--

[1] https://lists.gnu.org/archive/html/emacs-devel/2022-06/msg00444.html
[2] https://lists.gnu.org/archive/html/emacs-devel/2022-06/msg00553.html

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