From: Drew Adams <drew.adams@oracle.com>
To: Stefan Monnier <monnier@iro.umontreal.ca>,
"'Help-Gnu-Emacs (help-gnu-emacs@gnu.org)'"
<help-gnu-emacs@gnu.org>
Subject: RE: [External] : Use of an associated list with completing-read
Date: Sat, 20 Apr 2024 01:13:12 +0000 [thread overview]
Message-ID: <SJ0PR10MB54882D9B348472B5DD432397F30C2@SJ0PR10MB5488.namprd10.prod.outlook.com> (raw)
In-Reply-To: <jwvbk65rkzr.fsf-monnier+emacs@gnu.org>
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> > (setq-local tema-lugar
> > (append tema--lugar (list (cons lnum strg))))
>
> This is the classic recipe for poor scaling performance since the above
> operation takes time proportional to the length of the list, so if you
> execute this N times (in a loop), the loop builds a list of length N
> but takes time N² to do it. When N is small, noone notices, and as it gets
> large the performance starts to suck.
Heime:
One programming cliche for this is to
(1) start with a list that you create
(e.g., a let-binding to nil), so you
don't modify any existing list that
you might not want to mess with, (2)
use `nconc' instead of `append', to
append quickly (the _list structure_
is modified - destructive), (3) being
sure to set your list variable to the
result of each modification.
An even more common cliche for doing
the same thing is to do #1, then (2)
cons instead of append, and (3) when
finished adding list elements, do an
`nreverse' of the list you created.
That too is a destructive operation.
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next prev parent reply other threads:[~2024-04-20 1:13 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-18 23:48 Use of an associated list with completing-read Heime
2024-04-19 2:14 ` [External] : " Drew Adams
2024-04-19 2:59 ` Heime
2024-04-19 3:10 ` Heime
2024-04-19 15:10 ` Drew Adams
2024-04-19 19:09 ` Heime
2024-04-19 23:32 ` Stefan Monnier via Users list for the GNU Emacs text editor
2024-04-20 1:13 ` Drew Adams [this message]
2024-04-20 1:52 ` Stefan Monnier via Users list for the GNU Emacs text editor
2024-04-20 1:59 ` Emanuel Berg
2024-04-20 6:14 ` Heime
2024-04-20 6:37 ` Heime
2024-04-23 4:44 ` Jean Louis
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