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I was in correspondence with the author of a LaTeX package in which I volunteered code similar to the following (I have anonymised it so that it is not obvious what package):

        \csname saved@macro@state@named@#1\endcsname%
    \ifcsname saved@macro@state@named@#1\endcsname%
        \errmessage{Saved macro state named "#1" doesn't exist}%
        \csname saved@macro@state@named@#1\endcsname%

In their reply, one thing they said was that instead of writing #1 in your macros, you should write \detokenize{#1}, as it is safer. Why is it safer? What might go wrong if I don't?

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If you're sure that #1 will always be replaced with a string of ASCII characters, there's no difference. – egreg Jan 18 '14 at 13:41
@egreg 'Sure' is a risky business ;-) – Joseph Wright Jan 18 '14 at 15:26
@JosephWright People who monkey with category codes are on their own. – egreg Jan 18 '14 at 15:39
@egreg User input can legitimately contain ~ or _ with the underscore package loaded :-) – Joseph Wright Jan 18 '14 at 15:57
@JosephWright Let's say non TeX special characters, then; I don't consider underscore that creates more problems than it solves. – egreg Jan 18 '14 at 16:00
up vote 13 down vote accepted

If you have

\def!{\hspace{2in} \fbox{boo} \hspace{2in}}

then \csname foo!\endcsname is an error as the name doesn't expand to a sequence of character tokens, but \csname\detokenize{foo!}\endcsname is same as \csname foo\string!\endcsname and makes the token with name foo!

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