Cleaner way of making rows in a table dynamically appear

Question

So what I have works, but I am looking for a cleaner / better approach.

I have a titlepage which needs a \maketitle in the form of a table (Tabular actually). However, when options are missing they should just be removed from the table. Similarly if no options are given, no table should be printed.

For instance

\def\@author{Jane doe}
\def\@date{\today}
\def\@verifier{Joe Doe}

Should produce

While

\def\@author{Jane doe}
\def\@date{}
\def\@verifier{}

becomes

This is my current idea, presented in as minimal of an example as I could make

\documentclass{article}
\usepackage{etoolbox}
\usepackage{booktabs}
\makeatletter
    \def@author{}
    \def@date{}
    \def@verifier{}
    % Comment out the lines bellow to test
    \def@author{Jane doe}
    \def@date{\today}
    \def@verifier{Joe Doe}
\newcommand{\maketitletable}{
%
\newcommand{\authorname}{author}
\newcommand{\datename}{date}
\newcommand*{\verifiername}{verifier}
%
\ifstrempty{@author@date@verifier}{}{
    \noindent
    \begin{tabular}{p{0.2\textwidth} p{0.2\textwidth} p{\dimexpr 0.6\textwidth - 4\tabcolsep}}\toprule
        \ifdefempty{@author}{}{& \authorname{} & @author \}
        \ifdefempty{@date}{}{& \datename{} & @date \}
        \ifdefempty{@verifier}{}{& \verifiername{} & @verifier \}
      \bottomrule
    \end{tabular}%
    }
}
\makeatother
\begin{document}
    \maketitletable
\end{document}

Just for reference, In my real code I do something like the following (I have many more)

\usepackage{xparse}
\ExplSyntaxOn
    % Provide keys.
    \keys_define:nn { babylonia }
      {
        author         .tl_set:N  = \@author,
        author         .initial:n = {},
        date           .tl_set:N  = \@date,
        date           .initial:n = {},
        verifier       .tl_set:N  = \@verifier,
      }
    % Provide key setting command.
    \NewDocumentCommand\OUSsetup{ m }{
      \keys_set:nn { babylonia } { #1 }
    }
\ExplSyntaxOff

and then

\makeatletter
\renewcommand{\maketitle}{% 
...
minimal working example goes in here
...
}
\makeatother

Before finally setting

\OUSsetup{
  author    = Jane Doe,
  date      = 01.12.2021,
  verifier  = Joe Doe,
}
\begin{document}
\maketitle
\end{document}

I am guessing this makes no difference to how the table is implemented.

Answer 1

Here is a possible solution with tabularray package:

\documentclass{article}
\usepackage{etoolbox}
\usepackage{tabularray}
\UseTblrLibrary{booktabs}
\makeatletter
\def@author{}
\def@date{}
\def@verifier{}
\def\authorname{author}
\def\datename{date}
\def\verifiername{verifier}
\newcommand*{\mycheckempty}[1]{\ifcsempty{@#1}{}{\csuse{#1name}\strut}}
\newcommand{\maketitletable}{%
\ifstrempty{@author@date@verifier}{}{%
    \noindent
    \begin{booktabs}{
      colspec={X[2]X[2]X[6]},
      stretch=0, rowsep=0pt, column{2}={cmd=\mycheckempty},
    }
      \toprule
        & author   & @author   \
        & date     & @date     \
        & verifier & @verifier \
      \bottomrule
    \end{booktabs}%
    }%
}
\makeatother
\begin{document}
\makeatletter
\def@author{Jane doe}
\def@date{\today}
\def@verifier{Joe Doe}
\maketitletable
\bigskip
\def@author{Jane doe}
\def@date{}
\def@verifier{}
\maketitletable
\makeatother
\end{document}

Answer 2

The simplest solution (least modification to the existing code) would be to simply define an auxiliary macro (because of issues the macro must be defined outside, and some other issues with TikZ \foreach)

%! TEX program = lualatex
\documentclass{article}
\usepackage{etoolbox}
\usepackage{booktabs}
\makeatletter
\def@author{}
\def@date{}
\def@verifier{}
% Comment out the lines bellow to test
\def@author{Jane doe}
\def@date{\today}
\def@verifier{Joe Doe}
\newcommand\printrow[1]{%  ← this is the auxiliary macro ========
    \ifcsempty{@#1}{}{  & \csuse{#1name} & \csuse{@#1} \ }%
    %                     ↑ ↑ ↑ ↑ ↑ ↑ ↑    might be replaced with simply #1 if you're sure
}
\newcommand{\maketitletable}{
%
\newcommand{\authorname}{author}
\newcommand{\datename}{date}
\newcommand*{\verifiername}{verifier}
%
\ifstrempty{@author@date@verifier}{}{
    \noindent
    \begin{tabular}{p{0.2\textwidth} p{0.2\textwidth} p{\dimexpr 0.6\textwidth - 4\tabcolsep}}\toprule
        \printrow{author}  % ======== use it like this
        \printrow{date}
        \printrow{verifier}
      \bottomrule
    \end{tabular}%
    }
}
\makeatother
\begin{document}
    \maketitletable
\end{document}

Alternative solution with expl3.

%! TEX program = lualatex
\documentclass{article}
\usepackage{etoolbox}
\usepackage{booktabs}
\makeatletter
\def@author{}
\def@date{}
\def@verifier{}
% Comment out the lines bellow to test
\def@author{Jane doe}
\def@date{\today}
\def@verifier{Joe Doe}
\ExplSyntaxOn
\prg_generate_conditional_variant:Nnn \tl_if_empty:n {x} {F}
\cs_set_protected:Npn __process_item:n #1 {
    \tl_if_empty:cF {@#1} { & \use:c{#1name} & \use:c {@#1} \ }
}
\newcommand{\maketitletable}{
%
\newcommand{\authorname}{author}
\newcommand{\datename}{date}
\newcommand*{\verifiername}{verifier}
%
\tl_if_empty:xF{@author@date@verifier}{
    \noindent
    \begin{tabular}{p{0.2\textwidth} p{0.2\textwidth} p{\dimexpr 0.6\textwidth - 4\tabcolsep}}\toprule
        \clist_map_function:nN {author, date, verifier} __process_item:n
        \bottomrule
    \end{tabular}%
    }
}
\makeatother
\ExplSyntaxOff
\begin{document}
    \maketitletable
\end{document}

Note that using \clist_map_inline directly will not work (Misplaced \noalign.) because of some low level TeX reasons (roughly speaking, at high revel \\ \bottomrule does work, while \\ \relax \bottomrule doesn't, and \clist_map_inline does some unexpandable things between \\ and \bottomrule)