From: Stefan Monnier <monnier@iro.umontreal.ca>
To: emacs-devel@gnu.org
Subject: Re: expose XHASH [patch]
Date: Thu, 31 Mar 2016 17:52:51 -0400 [thread overview]
Message-ID: <jwvy48y2ufy.fsf-monnier+gmane.emacs.devel@gnu.org> (raw)
In-Reply-To: CAG7BparKZuRvtACRU2kPS9wyx3Yf4VgZ_LFjNZip5cGr1qkqxw@mail.gmail.com
> Please don't write that the example is stupid, it is just an
> example after all.
FWIW, I have bumped into various cases where I also needed to define
a hash for an equality function that's defined for example as (and (eq
(car x) (car y)) (eq (cdr x) (cdr y))). Worse yet: you say that "sxhash
_will_ work" but in reality it won't if the objects are later modified
by side-effects.
See for example:
(cl--generic-with-memoization
;; FIXME: Since the fields of `generic' are modified, this
;; hash-table won't work right, because the hashes will change!
;; It's not terribly serious, but reduces the effectiveness of
;; the table.
(gethash (cons generic methods)
cl--generic-combined-method-memoization)
from cl-generic.el. I wrote "It's not terribly serious", but IIRC there
can be cases where it causes real problems.
So a big "yes please" from me.
Stefan
next prev parent reply other threads:[~2016-03-31 21:52 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-31 19:29 expose XHASH [patch] Paul Pogonyshev
2016-03-31 21:52 ` Stefan Monnier [this message]
2016-03-31 22:43 ` Paul Eggert
2016-04-01 9:44 ` Paul Pogonyshev
2016-04-02 11:52 ` Paul Pogonyshev
2016-04-08 16:08 ` Paul Pogonyshev
2016-04-08 18:10 ` Stefan Monnier
2016-04-08 18:37 ` Paul Pogonyshev
2016-04-08 18:44 ` Stefan Monnier
2016-04-08 19:24 ` Paul Pogonyshev
2016-04-08 20:51 ` Stefan Monnier
2016-04-08 22:37 ` Paul Eggert
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