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Re: Differences between identical strings in Emacs lisp


From: Pascal J. Bourguignon
Subject: Re: Differences between identical strings in Emacs lisp
Date: Tue, 07 Apr 2015 02:10:09 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux)

Jürgen Hartmann <address@hidden> writes:

> What is the difference between the string represented by the constant "\xBA"
> and the result of (concat '(#xBA))?

    (mapcar 'multibyte-string-p (list "\xBA" (concat '(#xBA))))
    --> (nil t)

string-equal (and therefore string=) don't ignore the multibyte property
of a string.


You can use:

    (mapcar 'string-as-unibyte  (list "\xBA" (concat '(#xBA))))
    --> ("\272" "\302\272")

to see the difference.



Now, it's hard to say how to "solve" this problem, basically, you asked
for it: "\xBA" is not a valid way to write a string containing masculine
ordinal.

I guess you could extract back the bytes, and recreate the string
correctly:

    (map 'string 'identity (map 'list 'identity "\xBA"))
    --> "º"

    (string= (map 'string 'identity (map 'list 'identity "\xBA"))
             (concat '(#xBA)))
    --> t



(On the other hand, one might argue that having both unibyte and
multibyte strings in a lisp implementation is not a good idea, and
there's the opportunity for a big refactoring and simplification).

-- 
__Pascal Bourguignon__                 http://www.informatimago.com/
“The factory of the future will have only two employees, a man and a
dog. The man will be there to feed the dog. The dog will be there to
keep the man from touching the equipment.” -- Carl Bass CEO Autodesk


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