From: Stefan Monnier <monnier@iro.umontreal.ca>
To: emacs-devel@gnu.org
Subject: Re: creating unibyte strings
Date: Fri, 22 Mar 2019 10:23:20 -0400 [thread overview]
Message-ID: <jwvh8bvf1kk.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: 837ecrrqdm.fsf@gnu.org
>> >> Which reminds me: could someone add to the module API a primitive to
>> >> build a *unibyte* string?
>> > I don't like adding such a primitive. We don't want to proliferate
>> > unibyte strings in Emacs through that back door, because manipulating
>> > unibyte strings involves subtle issues many Lisp programmers are not
>> > aware of.
>>
>> I don't see what's subtle about "unibyte" strings, as long as you
>> understand that these are strings of *bytes* instead of strings
>> of *characters* (i.e. they're `int8[]` rather than `w_char_t[]`).
>
> That's the subtlety, right there. Handling such "strings" in Emacs
> Lisp can produce strange and unexpected results for someone who is not
> aware of the difference and its implications.
But this has nothing to do with the modules API: it's not more tricky
then when doing it purely in Elisp. Are you seriously suggesting we
deprecate unibyte strings altogether?
>> "Multibyte" strings are just as subtle (maybe more so even), yet we
>> rightly don't hesitate to offer a primitive way to construct them.
> Because we succeed to hide the subtleties in that case,
> so the multibyte nature is not really visible on the Lisp level,
> unless you try very hard to make it so.
Then I don't know what subtleties you're talking about.
Can you give some examples of the kinds of things you're thinking of?
>> > Instead, how about doing that via vectors of byte values?
>> What's the advantage? That seems even more convoluted: create a Lisp
>> vector of the right size (i.e. 8x the size of your string on a 64bit
>> system), loop over your string turning each byte into a Lisp integer
>> (with the reverted API, this involves allocation of an `emacs_value`
>> box), then pass that to `concat`?
> That's one way, but I'm sure I can come up with a simpler one. ;-)
I'm all ears.
>> It's probably going to be even less efficient than going through utf-8
>> and back.
> I doubt that. It's just an assignment. And it's a rare situation
> anyway.
Why do you think it's rare?
It's pretty common to receive non-utf-8 byte streams from the external world.
And when you do receive them, it can come at a very fast pace and become
temporarily anything but rare.
>> Think about cases where the module receives byte strings from the disk
>> or the network and need to pass that to `decode-coding-string`.
>> And consider that we might be talking about megabytes of strings.
> They don't need to decode, they just need to arrange for it to be
> UTF-8.
Three possibilities:
1- the C side string contains utf-8 text.
The module API provides just the right operation, we're good to go.
2- the C side string contains text in latin-1, big5, younameit.
The module API provides nothing convenient. Should we force our
module to link to C-side coding-system libraries to convert to utf-8
before passing it on to the Elisp, even though Emacs already has all
the needed facilities? Really?
3- The C side string contains binary data (say PNG images).
What does "arrange for it to be UTF-8" even mean?
-- Stefan
PS: The PNG case is not hypothetical at all, it's what prompted my request.
next prev parent reply other threads:[~2019-03-22 14:23 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-11 18:12 Oddities with dynamic modules Eli Zaretskii
2018-10-12 14:29 ` Kaushal Modi
2019-02-10 20:23 ` Philipp Stephani
2019-02-11 15:45 ` Eli Zaretskii
2019-02-11 16:04 ` Yuri Khan
2019-03-21 20:04 ` Philipp Stephani
2019-03-21 20:17 ` Eli Zaretskii
2019-03-21 20:32 ` Philipp Stephani
2019-03-21 20:46 ` Eli Zaretskii
2019-03-21 20:51 ` Philipp Stephani
2019-03-21 20:12 ` Philipp Stephani
2019-03-21 20:25 ` Eli Zaretskii
2019-03-21 20:34 ` Philipp Stephani
2019-03-21 20:51 ` Eli Zaretskii
2019-03-21 20:58 ` Philipp Stephani
2019-03-22 1:26 ` creating unibyte strings (was: Oddities with dynamic modules) Stefan Monnier
2019-03-22 7:41 ` Eli Zaretskii
2019-03-22 12:33 ` creating unibyte strings Stefan Monnier
2019-03-22 13:27 ` Eli Zaretskii
2019-03-22 14:23 ` Stefan Monnier [this message]
2019-03-22 15:11 ` Eli Zaretskii
2019-03-22 15:37 ` Stefan Monnier
2019-03-22 15:54 ` Eli Zaretskii
2019-03-24 14:51 ` Elias Mårtenson
2019-03-24 17:10 ` Eli Zaretskii
2019-03-25 1:47 ` Elias Mårtenson
2019-03-25 3:41 ` Eli Zaretskii
2019-03-26 10:23 ` Elias Mårtenson
2019-03-26 11:12 ` Stefan Monnier
2019-03-22 8:20 ` Oddities with dynamic modules Eli Zaretskii
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