cls Variable Fallback

Question

Since I am not experienced with writing cls so it may be a very simple question and is a duplicate but I cannot use the exact word to express it.

Here is what I want to achieve in this cls:

There are two commands, \author and instructor (this is defined in cls), each taking an argument.
Normally, they can be set separately.
However, if \author or \instructor is empty (i.e. \author{}, \instructor{}) or \author or \instructor is not defined by the user, they should use a fallback, \@author will be \@instructor or \@instructor be assigned \@author according to which one is missing.
If both are missed, maybe just do nothing.

This is a MnWE. It compiles with error. (Strangely, with my full cls, it compiles fine but the \if statement does not seem right and the result is wrong.)

\RequirePackage{filecontents}
\begin{filecontents*}{myclass.cls}
    \NeedsTeXFormat{LaTeX2e}
    \ProvidesClass{myclass}
    \LoadClass{article}
\let\@instructor\@empty
\newcommand{\instructor}[1]{\gdef\@instructor{#1}}

\newcommand{\test}{\@instructor}

\makeatletter
\if\@instructor\@empty
    \def\@instructor\@author % author is the instructor (if not specified)
\else
    \if\@author\@empty
        \def\@author\@instructor % instructor is the author (if not specified)
    \fi
\fi
\makeatother

\end{filecontents*}
\documentclass{myclass}
\author{Author Name}
% \instructor{Instructor Name}
\instructor{}
\begin{document}
    \test{}
\end{document}

\ifx not \if (in both cases) and \let not \def you can not do \def\something\somethingelse t needs braces — David Carlisle, Mar 19 '22 at 08:05
@DavidCarlisle Thanks a million for pointing out the right direction! — Teddy van Jerry, Mar 19 '22 at 08:55

score 0 · Accepted Answer · answered Mar 19 '22 at 08:54

Thanks to David Carlisle, I finally solved the problem. The difference between \ifx and \if is pointed out here.

The test file needs some changes so as to demonstrate the function (here I use the \maketitle command as an example):

\RequirePackage{filecontents}
\begin{filecontents*}{myclass.cls}
\NeedsTeXFormat{LaTeX2e}
\ProvidesClass{myclass}
\LoadClass{article}
\let@instructor@empty
\newcommand{\instructor}[1]{\gdef@instructor{#1}}
\makeatletter
\renewcommand\maketitle{
    \ifx@instructor@empty
        \let@instructor@author % author is the instructor (if not specified)
    \else
        \ifx@author@empty
            \let@author@instructor % instructor is the author (if not specified)
        \fi
    \fi
    @instructor
}
\makeatother
\end{filecontents*}
\documentclass{myclass}
\author{Author Name}
% \instructor{Instructor Name}
\instructor{}
\begin{document}
    \maketitle
\end{document}

which now works out fine.

For the whole cls file, this class has been uploaded to CTAN. — Teddy van Jerry, Mar 21 '22 at 04:33

cls Variable Fallback

1 Answers1