From: Ihor Radchenko <yantar92@gmail.com>
To: Andreas Schwab <schwab@suse.de>
Cc: emacs-devel@gnu.org
Subject: Re: Comparing hash table objects
Date: Wed, 08 Jun 2022 17:17:31 +0800 [thread overview]
Message-ID: <87leu7tsyc.fsf@localhost> (raw)
In-Reply-To: <mvmr13zedxl.fsf@suse.de>
Andreas Schwab <schwab@suse.de> writes:
> On Jun 08 2022, Ihor Radchenko wrote:
>
>> Is there any way to compare objects containing hash tables for equality?
>
> Hash tables are only equal if eq.
This is somewhat unexpected.
To clarify my problem, let me explain in more details what I am trying
to achieve.
Currently, I am using structs to store objects with properties:
(setq obj1 (type (:key1 val1 :key2 val2 ...)))
(setq obj2 (type (:key1 val1 :key2 val2 ...))) ;; the same properties
With this approach, I can easily compare objects with (equal obj1 obj2),
use them as hash table keys, etc.
However, when the number of properties increases, :key access becomes
slow because plist-get has O(N) complexity.
The natural solution is using hash tables:
(setq obj1 (type (make-hash-table)))
(setq obj2 (type (make-hash-table)))
;; fill the hash tables with :keyN valN pairs
Now, I can retrieve the :key in O(1).
However, all of a sudden, I am unable to compare two objects with this
new internal structure. (equal obj1 obj2) returns nil.
The described behavior potentially generates a lot of room for errors.
It is relatively easy to remember that different hash table objects are
never equal (only equal when also eq). However, when the hash tables are
hidden inside a struct, it is easy to overlook that the structs cannot
be compared with equal as usual.
Best,
Ihor
next prev parent reply other threads:[~2022-06-08 9:17 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-08 8:41 Comparing hash table objects Ihor Radchenko
2022-06-08 8:51 ` Andreas Schwab
2022-06-08 9:17 ` Ihor Radchenko [this message]
2022-06-10 22:45 ` Richard Stallman
2022-06-11 5:52 ` Ihor Radchenko
2022-06-11 16:04 ` Stefan Monnier
2022-06-12 9:16 ` Ihor Radchenko
2022-06-12 23:55 ` Sam Steingold
2022-06-13 13:02 ` Stefan Monnier
2022-06-13 16:18 ` Sam Steingold
2023-05-15 5:56 ` bug#63513: [PATCH] Make persist-defvar work with records and hash tables Joseph Turner via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-05-15 11:31 ` Eli Zaretskii
2023-05-23 20:14 ` Joseph Turner via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-09-02 23:54 ` Joseph Turner via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-09-03 6:08 ` Eli Zaretskii
2023-09-04 0:29 ` Joseph Turner via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-09-04 11:33 ` Eli Zaretskii
2023-09-04 15:57 ` Joseph Turner via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-09-04 17:05 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-09-04 22:28 ` Joseph Turner via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-09-05 21:06 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-09-08 11:30 ` Ihor Radchenko
2023-09-08 11:58 ` Eli Zaretskii
2023-09-08 12:06 ` Ihor Radchenko
2023-09-08 12:46 ` Eli Zaretskii
2023-09-08 12:51 ` Ihor Radchenko
2023-09-08 16:36 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-09-08 17:06 ` Ihor Radchenko
2023-09-08 17:10 ` Joseph Turner via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-09-09 10:01 ` Ihor Radchenko
2023-09-09 10:15 ` Daniel Mendler
2023-09-09 11:35 ` Ihor Radchenko
2023-09-09 11:57 ` Daniel Mendler
2023-09-09 12:12 ` compat.el and Emacs unstable master branch features (was: bug#63513: [PATCH] Make persist-defvar work with records and hash tables) Ihor Radchenko
2023-09-09 12:29 ` Daniel Mendler
2023-09-09 16:52 ` Joseph Turner
2023-09-11 8:45 ` Ihor Radchenko
2023-09-12 10:02 ` compat.el and Emacs unstable master branch features Philip Kaludercic
2023-09-12 10:27 ` Daniel Mendler
2023-09-13 10:31 ` Philip Kaludercic
2023-09-13 17:11 ` Daniel Mendler
2023-10-15 8:43 ` Ihor Radchenko
2023-10-15 12:09 ` Philip Kaludercic
2023-09-05 15:08 ` bug#63513: [PATCH] Make persist-defvar work with records and hash tables phillip.lord
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