Using \detokenize and underscore in combination with \listoffigures

Question

I've been using a macro X similar to

\newcommand{\X}[1]{{\ttfamily{\detokenize{#1}}}}

to format certain words that may contain an underscore, without having to escape with \_. This worked until I used it in a \caption. This results in an error with both pdflatex and lualatex (! Missing $ inserted.). Consider this MWE:

\documentclass{article}

\newcommand{\X}[1]{{\ttfamily{\detokenize{#1}}}}

\begin{document}    
\listoffigures
\begin{figure}
  \centering
  \caption{One \X{a_b} Two}
\end{figure}
\end{document}

Do I have to use a different / more elaborate solution for X or should I just escape the underscores generally? I am more interested in the best practices instead of a very clever hack.

Answer 1

You need the command to be robust, otherwise the annotation in the .lof file becomes

\contentsline {figure}{\numberline {1}{\ignorespaces One \texttt {a_b} Two}}{1}%

(I changed the syntax from {\ttfamily...} to \texttt{...}, which is better). As you see, the \detokenize has been applied and disappeared.

On the other hand, if you do

\newcommand{\X}{}% for safety
\DeclareRobustCommand{\X}[1]{\texttt{\detokenize{#1}}}

the annotation would be

\contentsline {figure}{\numberline {1}{\ignorespaces One \X {a_b} Two}}{1}%

and the problem would not show.

Alternatively, use \protect\X when in a moving argument.