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

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

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

[Message part 1 (text/plain, inline)]

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)]

[Message part 3 (text/plain, inline)]

--

[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

Message #8 received at 56199 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Mattias Engdegård <mattiase <at> acm.org>
Cc: 56199 <at> debbugs.gnu.org
Subject: Re: bug#56199: hash table equality predicate [PATCH]
Date: Fri, 24 Jun 2022 20:21:45 +0200

Mattias Engdegård <mattiase <at> acm.org> writes:

> 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.)

I can't ever recall wanting to compare two hash tables for equality
(like, that's not what you use a hash table for), but since people have
apparently been reimplementing this a lot, then I'm for including it.

And the implementation looks nice.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Message #13 received at 56199-done <at> debbugs.gnu.org (full text, mbox):

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.

Message #16 received at 56199-done <at> debbugs.gnu.org (full text, mbox):

From: Jean Louis <bugs <at> gnu.support>
To: Mattias Engdegård <mattiase <at> acm.org>,
 Lars Ingebrigtsen <larsi <at> gnus.org>
Cc: 56199-done <at> debbugs.gnu.org
Subject: Re: bug#56199: hash table equality predicate [PATCH]
Date: Sun, 26 Jun 2022 14:30:13 +0000

I use database stored hashes where new edited and updated one shall be compared to the stored one.

This will become useful.


Jean

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