Re: using empty_string as the only "" string

[Richard Stallman]

    How you can modify the multibyteness of an empty string ? You can't aset
    multibyte char (as well as anything else) into empty string, and conversion
    functions like 'string-make-unibyte' or 'string-to-multibyte' always creates
    new strings instead of touching an argument. Moreover, since "" is a
    no-op in concatenation operations, it may be silently discarded without
    looking into internal structure, isn't it ?

The multibyteness of a null string does affect concatenation.
But you are right, I believe, that it is impossible to alter the
multibyteness of an existing null string.  You can't do it with aset
because there are no positions you could store in.

Thus, it would be necessary to keep one canonical null unibyte string
and one canonical null multibyte string.