GNU bug report logs - #58168
string-lessp glitches and inconsistencies

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Message #50 received at 58168 <at> debbugs.gnu.org (full text, mbox):

From: Mattias Engdegård <mattias.engdegard <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 58168 <at> debbugs.gnu.org
Subject: Re: bug#58168: string-lessp glitches and inconsistencies
Date: Sat, 1 Oct 2022 21:57:45 +0200

1 okt. 2022 kl. 07.22 skrev Eli Zaretskii <eliz <at> gnu.org>:

> It depends on the use case, but in general I see no problem with
> signaling errors when we cannot produce reasonably correct results.
> For example, string-to-unibyte does signal an error in some cases.

That's fine because that function is documented to do so and always has, but making previously possible comparisons raise errors shouldn't be done lightly.

Comparison between objects is not only useful when someone cares about their order, as in presenting a sorted list to the user. Often what is important is an ability to impose an order, preferably total, for use in building and searching data structures. I came across this bug when implementing a string set.

>> It's also a matter of performance -- string< has been improved recently but currently we compare text in Latin and Swahili much faster than French and Arabic; it would be nice to close that gap. UTF-8 is designed so that comparing strings by scalar values can be done byte-wise, but the way we encode raw bytes make them sort right between ASCII and Latin-1. Given that the specific order doesn't matter much, we could just run with that.
> 
> I see no reason to make comparison of unibyte and multibyte strings
> perform better.

Actually I was talking about multibyte-multibyte comparisons.

You were probably thinking about comparisons between unibyte strings that contain raw bytes and multibyte strings, and those are indeed not very performance-sensitive. However there is no way to detect whether a unibyte string contains non-ASCII chars without looking at every byte, and comparing unibyte ASCII with multibyte is definitely of interest. Strings are still unibyte by default.

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