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Re: case-insensitive string comparison

From: Sam Steingold
Subject: Re: case-insensitive string comparison
Date: Tue, 19 Jul 2022 18:47:14 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/29.0.50 (darwin)

> * Roland Winkler <jvaxyre@tah.bet> [2022-07-19 14:39:32 -0500]:
> On Tue, Jul 19 2022, Sam Steingold wrote:
>> Specifically, I would like to add
>> (defun string-equal-ignore-case (s1 s2)
>>   "Like `string-equal', but case-insensitive.
>> Upper-case and lower-case letters are treated as equal.
>> Unibyte strings are converted to multibyte for comparison."
>>   (eq t (compare-strings s1 0 nil s2 0 nil t)))
>> to subr.el next to `string-prefix-p' - is this okay?
> I have run into this problem fairly often that I needed case-insensitive
> string comparison, and I believe various elisp packages include a
> "private" version of the above.  I always felt that
> `(eq t (compare-strings s1 0 nil s2 0 nil t))' was a crutch for this
> common problem.  Would it make sense to give the built-in function
> string-equal an optional arg ignore-case?

No, because I need to be able to pass `string-equal-ignore-case' to
things like `cl-find' as `:test' &c.

Also, if you look at fns.c, `string-equal' is basically `memcmp', while
`compare-strings' is way more complex.

PS. Actually, compare-strings/ignore_case is broken because it does,
essentially, upcase both arguments, see 

Sam Steingold (http://sds.podval.org/) on darwin Ns 10.3.2113
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