GNU bug report logs - #43598
replace-in-string: finishing touches

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Mattias Engdegård <mattiase <at> acm.org>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#43598: closed (replace-in-string: finishing touches)
Date: Sun, 27 Sep 2020 16:15:02 +0000

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Your message dated Sun, 27 Sep 2020 18:14:36 +0200
with message-id <0DD2B3C3-8ADA-4F90-815C-84D27AE03344 <at> acm.org>
and subject line Re: bug#43598: replace-in-string: finishing touches
has caused the debbugs.gnu.org bug report #43598,
regarding replace-in-string: finishing touches
to be marked as done.

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From: Mattias Engdegård <mattiase <at> acm.org>
To: bug-gnu-emacs <at> gnu.org
Cc: Lars Ingebrigtsen <larsi <at> gnus.org>
Subject: replace-in-string: finishing touches
Date: Thu, 24 Sep 2020 22:52:06 +0200

The new replace-in-string function is welcome but needs a few tweaks before we can call it done:

1. It doesn't quite work correctly with raw bytes:

  (replace-in-string "\377" "x" "a\377b")
  => "axb"
  (replace-in-string "\377" "x" "a\377ø")
  => "a\377ø"

The easiest solution is to reimplement it in terms of replace-regexp-in-string for now, and optimise it later (although I feel a bit bad undoing Lars's pretty handiwork...)

We have messy semantics here, because string-equal does not equate "\377" and (string-to-multibyte "\377"), but string-match-p does...

2. It is documented always to return a new string, but that's a tad over-generous nowadays; very few string functions do that. If we drop that guarantee, we get some optimisation opportunities:

- it can return the input string itself if no matches were found (a fairly common case)
- it can be marked pure, not just side-effect-free, so that the byte compiler can constant-propagate through calls to it

3. The name is somewhat unfortunate since a function by that name in XEmacs uses regexp matching.
In fact, the new function probably broke prolog-mode because of that (see prolog-replace-in-string).
While we can fix prolog-mode, we can't easily fix code outside the Emacs tree that may have similar problems.

Perhaps we should rename it to string-replace, in line with the modern naming convention discussed some time ago.

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From: Mattias Engdegård <mattiase <at> acm.org>
To: Lars Ingebrigtsen <larsi <at> gnus.org>
Cc: 43598-done <at> debbugs.gnu.org
Subject: Re: bug#43598: replace-in-string: finishing touches
Date: Sun, 27 Sep 2020 18:14:36 +0200

27 sep. 2020 kl. 14.02 skrev Lars Ingebrigtsen <larsi <at> gnus.org>:

> Please go ahead and apply.

Applied, thank you.

Looks like we are done now. string-replace seems to be substantially faster than replace-regexp-in-string.
Good job!

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