12

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):

\makeatletter
\newcommand{\savemacrostatewithname}[1]{%
    \expandafter\let%
        \csname saved@macro@state@named@#1\endcsname%
        \package@internal@macro%
}
\newcommand{\restoremacrostatewithname}[1]{%
    \ifcsname saved@macro@state@named@#1\endcsname%
    \else%
        \errmessage{Saved macro state named "#1" doesn't exist}%
    \fi%
    \expandafter\let%
        \expandafter\package@internal@macro%
        \csname saved@macro@state@named@#1\endcsname%
}
\makeatother

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?

5
  • If you're sure that #1 will always be replaced with a string of ASCII characters, there's no difference.
    – egreg
    Jan 18, 2014 at 13:41
  • @egreg 'Sure' is a risky business ;-)
    – Joseph Wright
    Jan 18, 2014 at 15:26
  • @JosephWright People who monkey with category codes are on their own.
    – egreg
    Jan 18, 2014 at 15:39
  • @egreg User input can legitimately contain ~ or _ with the underscore package loaded :-)
    – Joseph Wright
    Jan 18, 2014 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, 2014 at 16:00

1 Answer 1

13

If you have

\catcode`\!=\active
\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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