Re: Why does using aset sometimes output raw bytes?

[Stephen Berman <stephen.berman@gmx.net>]

On Sun, 09 Dec 2018 19:12:32 +0200 Eli Zaretskii <eliz@gnu.org> wrote:

>> From: Stephen Berman <stephen.berman@gmx.net>
>> Cc: help-gnu-emacs@gnu.org
>> Date: Sun, 09 Dec 2018 16:46:01 +0100
>> 
>> > s0 and s2 originally include only pure ASCII characters, so they are
>> > unibyte strings.  Try making them multibyte before using aset.
>> 
>> Thanks, that works.  But why are raw bytes inserted only with some
>> multibyte strings (e.g. with "äöüß" but not with "ſðđŋ")?
>
> Because ſ doesn't fit in a single byte, so when you insert it, the
> entire string is made multibyte, and then the other characters are
> inserted into a multibyte string.

This seems to imply that ä, ö, ü and ß do fit in a single byte?  Yet
(multibyte-string-p "äöüß") returns t.  So I still don't understand.

>> Also, is there some way to ensure a string is handled as multibyte
>> if it's not known what characters it contains?  E.g., s0 in my
>> example sexp could be bound to some string by a function call and
>> before applying the function it is not known if the string is
>> multibyte;
>
> You should generally keep away of such situations, but you don't tell
> enough about what you are trying to accomplish to give more practical
> advice.

Nothing serious, just some experimenting.

> To answer your question: you can test whether a string is multibyte
> with multibyte-string-p, and you can make it multibyte if not.  The
> only problematic situation is when a unibyte string includes non-ASCII
> bytes; what is TRT in that situation depends on the situation.
>
>> is there some way in Lisp to say "treat the value of s0 as multibyte
>> (regardless of what characters it contains)"?
>
> Not that I know of, no.  And I don't really understand how could such
> a thing exist: how do you "treat as multibyte" an arbitrary byte that
> is beyond 127 decimal?

Actually, for the code I was experimenting with, it seems to suffice to
use (make-string len 128) as the input to aset (before, I had used
(make-string len 32), which led to raw bytes being displayed).
>
>> Also "aous" is also pure ASCII, so why don't raw bytes get inserted with
>> (insert (aset "aous" i (aref "äöüß" i)))?
>
> This inserts characters one by one into the current buffer, and the
> buffer is multibyte, so Emacs does the conversion.  IOW, you don't
> insert the string, you insert individual characters which aset
> returns.

Ah, this makes sense.  Thanks.

Steve Berman