Re: distinguishing multibyte/unibyte ASCII

["Toke Høiland-Jørgensen" <toke@toke.dk>]

Stefan Monnier <monnier@IRO.UMontreal.CA> writes:

>> If you just generate an ASCII string from ASCII characters, it will
>> usually be unibyte.  If you take it as a substring from a multibyte
>> buffer, it will usually be multibyte.
>
> And it's arguably a wart in Emacs's handling of chars-vs-bytes.
> But it's kind of hard to fix now.
>
> At some point I tried to change this handling (not exactly fix it) by
> treating multibyte ASCII strings specially (it's easy to recognize by
> checking that the char length is equal to the byte length and both are
> readily available in the "struct Lisp_String" object).  Then when we
> read an ASCII string, instead of making it unibyte, I'd keep it as
> multibyte.  And then change things like "concat" so that those "ASCII
> multibyte" strings don't force the result to be multibyte.
>
> My local Emacs still runs with those changes, but in the end I don't
> think the result is really better (or sufficiently better to justify
> the subtle incompatibilities it introduces).
>
> [ Also, I wouldn't be surprised to hear that such a change causes real
>   problems with utf-7 or EBCDIC, or other systems where decoding/encoding
>   a string of bytes/chars all <127 is not a no-op.  ]

Isn't Unicode fun? :)

-Toke