From: Stefan Monnier <monnier@iro.umontreal.ca>
To: daanturo <daanturo@gmail.com>
Cc: emacs-devel@gnu.org
Subject: Re: A function to take the regexp-matched subsring directly
Date: Sun, 30 Oct 2022 11:52:19 -0400 [thread overview]
Message-ID: <jwvr0yp2tz5.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <d7cf5a87-b427-fa3f-a3dd-c370689b8204@gmail.com> (daanturo@gmail.com's message of "Sun, 30 Oct 2022 22:17:00 +0700")
> +;;;###autoload
> +(defun regexp-match (regexp string &optional n)
> + "Return the N -th matched substring for REGEXP in STRING.
> +N defaults to 0 (the whole match).
> +
> +This function does not change the match data."
> + (declare (pure t) (side-effect-free t))
> + (let ((n (or n 0)))
> + (save-match-data
> + (when (string-match regexp string)
> + (match-string n string)))))
`save-match-data` is costly and extremely rarely needed.
So I'd much rather not save it here.
> + (save-match-data
> + (when (string-match regexp string)
> + (let ((match-index (1- (/ (length (match-data)) 2)))
> + matches)
> + (while (<= 0 match-index)
> + (push (match-string match-index string) matches)
> + (setq match-index (1- match-index)))
> + matches))))
I suspect it'd be more efficient to iterate directly on the `match-data` rather
than on an integer (which suffers from an O(N²) complexity).
Stefan
next prev parent reply other threads:[~2022-10-30 15:52 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-30 15:17 A function to take the regexp-matched subsring directly daanturo
2022-10-30 15:45 ` Philip Kaludercic
2022-10-30 16:46 ` daanturo
2022-10-30 17:26 ` Philip Kaludercic
2022-10-30 15:52 ` Stefan Monnier [this message]
2022-10-30 17:16 ` daanturo
2022-10-30 22:01 ` Stefan Monnier
2022-10-31 3:47 ` daanturo
2022-10-30 17:29 ` Philip Kaludercic
2022-10-30 22:07 ` Stefan Monnier
2022-10-31 8:56 ` Mattias Engdegård
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