Using \protect to generalise definitions of starred commands?

Question

This very helpful answer led me to define my own starred commands. However, in order to use my commands in, for example, headings, after a round of strange almost frightening thoughts, I managed to arrive at the following (MWE):

\documentclass{article}
\makeatletter
\def\testone{\@ifstar\@dothis\@@dothat}
\def\testtwo{\protect\@ifstar\protect\@dothis\protect\@@dothat}
\def\@dothis#1{#1}
\def\@@dothat#1{#1}
\makeatother
\begin{document}
\section{\testone{abc}} % does not work
\testone{abc} % works
\section{\testtwo{abc}} % works
\testtwo{abc} % works
\end{document}

I am still struggling to percolate TeX's expansion mechanisms and, hence, would be thankful for an answer about why my definition \test... requires these \protects to work in headings? Thanks.

Have you tried \NewDocumentCommand or \NewExpandableDocumentCommand and friends with an s-type (starred) argument? — User23456234, Feb 13 '24 at 13:13
Thanks for your hint. No, actually not. Haven't even been aware of these. Are these (La)TeX primitives and working with LuaTeX as well? — mfg, Feb 13 '24 at 13:15
These are part of newer LaTeX kernels. See usrguide.pdf current version for more information. — cabohah, Feb 13 '24 at 13:17

score 2 · Answer 1 · answered Feb 13 '24 at 16:36

\protect is wrong in those places.

If you want to make \testtwo robust, you need to use

\newcommand{\testtwo}{}% for safety against redefining
\DeclareRobustCommand{\testtwo}{\@ifstar\@dothis\@@dothat}

But it's simpler to use \NewDocumentCommand:

\NewDocumentCommand{\test}{sm}{%
  \IfBooleanTF{#1}{% there is a *
    called #1 with *%
  }{% no star
    called #1 without *%
  }%
}

See texdoc usrguide for more information about \NewDocumentCommand.

Thx, @egreg, works smoothly. The usrguide helps me to revise my "old" LaTeX practices. — mfg, Feb 13 '24 at 22:11

Using \protect to generalise definitions of starred commands?

1 Answers1