GNU bug report logs - #23902
25.1.50; Strange warning on string-collate-equalp's docstring

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Message #82 received at 23902 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: oscarfv <at> telefonica.net (Óscar Fuentes)
Cc: michael_heerdegen <at> web.de, rgm <at> gnu.org, 23902 <at> debbugs.gnu.org
Subject: Re: bug#23902: 25.1.50;
 Strange warning on string-collate-equalp's docstring
Date: Sun, 10 Jul 2016 05:40:25 +0300

> From: oscarfv <at> telefonica.net (Óscar Fuentes)
> Cc: Glenn Morris <rgm <at> gnu.org>,  michael_heerdegen <at> web.de,  23902 <at> debbugs.gnu.org
> Date: Sat, 09 Jul 2016 23:36:37 +0200
> 
> Eli Zaretskii <eliz <at> gnu.org> writes:
> 
> > But they can reason this way instead:
> >
> > "I want to compare two file names.
> > Collation is a way to compare strings, for example the man page for
> > strcoll says the function returns zero if one string is equal to the
> > other.
> > And Emacs just learned how to use collation to compare strings, it
> > has this great new function string-collate-equalp.
> > Therefore, let's use string-collate-equalp for comparing two file
> > names."
> 
> This implies that the user knows about string comparisons with collation
> but he is a complete ignoramus about file systems. A bit unrealistic.

I'm not sure.  People might know a lot about strings, but not how the
filesystem stores file names.

> >> And suppose I have two strings, and want to know if they are equal,
> >> respecting my locale's convention about characters that are not
> >> literally identical, but have the same meaning. I should use
> >> string-collate-equalp for this. This is true whether the strings
> >> represent the names of elephants in a zoo, or files on a disk.
> >
> > And that is exactly the fallacy that the note warns against.  Because
> > filesystems don't compare as equal characters that have the same
> > meaning, they compare bytes in a byte stream that is the file name in
> > its raw byte form, as recorded on disk.
> 
> I think that Glenn is saying that you can compare file names for other
> purposes than knowing if they name the same file.

Then it's not "equality", it's "equivalence".

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