Re: (aset UNIBYTE-STRING MULTIBYTE-CHAR)

[Harald Hanche-Olsen <hanche@math.ntnu.no>]

My message on this topic of a week ago elicited no responses, so I did
a little more research on my own (which I should have done in the
first place, maybe). This time I hope to see some discussion:

+ Harald Hanche-Olsen <hanche@math.ntnu.no>:

> This works as it should in the latest CVS:
> 
> (setq foo (make-string 4 ?a))
> (aset foo 1 ?€) ; <= that's a euro sign
> 
> But this fails:
> 
> (setq foo (make-string 4 ?a))
> (aset foo 1 ?å)
> (aset foo 1 ?€) ; => Error: args out of range

I went back in the mail archives and read the whole thread (it was in
February and April this year), and I realize that the whole idea of
changing a unibyte string into a multibyte one on the fly in order to
support aset on them is somewhat controversial. Be that as it may, the
above example shows that the fix put in by Kenichi Handa does not fix
it right. Moreover, it is clear from the commit message that he was
well aware of this limitation at the time:

Working file: data.c
revision 1.291
date: 2008-04-17 03:10:58 +0200;  author: handa;  state: Exp;  lines: +11 -1;  commitid: yW6gyKxwbZ4EPoZs;
(Faset): Allow setting a multibyte character in an
ASCII-only unibyte string.

It seems to me that in order to get it right, one has to reallocate
the data in the case of a non-ASCII-only unibyte string, using
code like what is already there for the case when aset replaces an
ASCII character with a non-ASCII one (which will increase the byte
count of the string). The end result will be ugly and inefficient, but
I see no other way if we are going to lay this one to rest.

Comments?

- Harald