multicolumn with trailing cell separator in NiceTabular

Question

For a variety of reasons, I migrate some tabulars to NiceTabular. One of them looks like this:

\documentclass{article}
\makeatletter
\newsavebox\saved@arstrutbox
\newcommand{\setarstrut}[1]{%
  \noalign{%
    \begingroup
      \global\setbox\saved@arstrutbox\copy@arstrutbox
      #1%
      \global\setbox@arstrutbox\hbox{%
        \vrule @height\arraystretch\ht\strutbox
               @depth\arraystretch \dp\strutbox
               @width\z@
      }%
    \endgroup
  }%
}
\newcommand{\restorearstrut}{%
  \noalign{%
    \global\setbox@arstrutbox\copy\saved@arstrutbox
  }%
}
\makeatother
\begin{document}
  \begin{tabular}{c@{/}c}
    \setarstrut{\tiny}
    \multicolumn{1}{c@{\tiny/}}{\tiny\textbf{droggel}} & \tiny\textbf{jug} \ \restorearstrut \hline
    23 & 42
  \end{tabular}
\end{document}

The header is mostly taken from this answer about making rows smaller. What I do is that I render the first row smaller than the others. Since I use the separator character / between the columns, that should also be rendered smaller. To facilitate this, I add a \multicolumn that replaces the original separator with a tiny one.

Now I switch out tabular with NiceTabular:

\documentclass{article}
\usepackage{nicematrix}
\makeatletter
\newsavebox\saved@arstrutbox
\newcommand{\setarstrut}[1]{%
  \noalign{%
    \begingroup
      \global\setbox\saved@arstrutbox\copy@arstrutbox
      #1%
      \global\setbox@arstrutbox\hbox{%
        \vrule @height\arraystretch\ht\strutbox
               @depth\arraystretch \dp\strutbox
               @width\z@
      }%
    \endgroup
  }%
}
\newcommand{\restorearstrut}{%
  \noalign{%
    \global\setbox@arstrutbox\copy\saved@arstrutbox
  }%
}
\makeatother
\begin{document}
  \begin{NiceTabular}{c@{/}c}
    \setarstrut{\tiny}
    \multicolumn{1}{c@{\tiny/}}{\tiny\textbf{droggel}} & \tiny\textbf{jug} \ \restorearstrut \hline
    23 & 42
  \end{NiceTabular}
\end{document}

Compiling this yields:

! Package array Error: Empty preamble: `l' used.
See the array package documentation for explanation.
Type  H <return>  for immediate help.
 ...
l.29 ...column{1}{c@{\tiny/}}{\tiny\textbf{droggel}}
                                                   & \tiny\textbf{jug} \ \r...

The error comes from the @{\tiny/} bit of the multicolumn argument. If I delete this, the code renders but the / is obviously gone.

How can I migrate this properly to NiceTabular while keeping the separator setup?

Answer 1

I have written a new version of nicematrix (v 5.17 of 2021-07-01). With that new version, the command \multicolumn should work as expected in the environments of nicematrix such as {NiceTabular}.

\documentclass{article}
\usepackage{nicematrix}
\makeatletter
\newsavebox\saved@arstrutbox
\newcommand{\setarstrut}[1]{%
  \noalign{%
    \begingroup
      \global\setbox\saved@arstrutbox\copy@arstrutbox
      #1%
      \global\setbox@arstrutbox\hbox{%
        \vrule @height\arraystretch\ht\strutbox
               @depth\arraystretch \dp\strutbox
               @width\z@
      }%
    \endgroup
  }%
}
\newcommand{\restorearstrut}{%
  \noalign{%
    \global\setbox@arstrutbox\copy\saved@arstrutbox
  }%
}
\makeatother
\begin{document}
  \begin{NiceTabular}{c@{/}c}
    \setarstrut{\tiny}
    \multicolumn{1}{c@{\tiny/}}{\tiny\textbf{droggel}} & \tiny\textbf{jug} \ \restorearstrut \hline
    23 & 42
  \end{NiceTabular}
\end{document}