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bug#58168: string-lessp glitches and inconsistencies
From: |
Eli Zaretskii |
Subject: |
bug#58168: string-lessp glitches and inconsistencies |
Date: |
Sun, 02 Oct 2022 08:36:46 +0300 |
> From: Mattias Engdegård <mattias.engdegard@gmail.com>
> Date: Sat, 1 Oct 2022 21:57:45 +0200
> Cc: 58168@debbugs.gnu.org
>
> 1 okt. 2022 kl. 07.22 skrev Eli Zaretskii <eliz@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.
I didn't say "lightly", nor do I think so. We need to discuss
specific use cases.
An alternative is to always convert unibyte non-ASCII strings to their
multibyte representation before comparing.
> 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.
Always converting to multibyte handles this case, doesn't it?
> >> 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.
Then why did you mention raw bytes? their multibyte representation
presents no performance problems, AFAIU.
> 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.
You can compare under the assumption that a unibyte string is
pure-ASCII until you bump into the first non-ASCII one. If that
happens, abandon the comparison, convert the unibyte string to its
multibyte representation, and compare again.
- bug#58168: string-lessp glitches and inconsistencies, Eli Zaretskii, 2022/10/01
- bug#58168: string-lessp glitches and inconsistencies, Mattias Engdegård, 2022/10/01
- bug#58168: string-lessp glitches and inconsistencies,
Eli Zaretskii <=
- bug#58168: string-lessp glitches and inconsistencies, Mattias Engdegård, 2022/10/06
- bug#58168: string-lessp glitches and inconsistencies, Eli Zaretskii, 2022/10/06
- bug#58168: string-lessp glitches and inconsistencies, Mattias Engdegård, 2022/10/07
- bug#58168: string-lessp glitches and inconsistencies, Eli Zaretskii, 2022/10/08
- bug#58168: string-lessp glitches and inconsistencies, Mattias Engdegård, 2022/10/14
- bug#58168: string-lessp glitches and inconsistencies, Eli Zaretskii, 2022/10/14