Replace \tabularnewline with \hline?

Question

If I've the following code that is autogenerated (adapted here for sharing) from another tool, that I cannot modify,:

\documentclass[oneside,a4paper]{book}

\usepackage{longtable}
\usepackage{tablefootnote}
\usepackage{booktabs}

\begin{document}

\begin{longtable}[]{@{}ll@{}}
\toprule
\begin{minipage}[b]{0.29\columnwidth} Value\strut \end{minipage} & \begin{minipage}[b]{0.65\columnwidth} Description\strut \end{minipage}\tabularnewline
\midrule
\endhead
\begin{minipage}[t]{0.29\columnwidth} \textbf{Value 1}\strut \end{minipage} & \begin{minipage}[t]{0.65\columnwidth} Some details for 1\strut \end{minipage}\tabularnewline
\begin{minipage}[t]{0.29\columnwidth} \textbf{Value 2}\strut \end{minipage} & \begin{minipage}[t]{0.65\columnwidth} Some details for 2\strut \end{minipage}\tabularnewline
\bottomrule
\end{longtable}
\end{document}

Is there a way that I can easily replace \tabularnewline with \hline in the latex preamble somehow?

I've tried things like this, but with no success. Relax seems to work, but the switch to hline does not.

\let\toprule\hline
\let\midrule\hline
\let\bottomrule\relax
\let\tabularnewline\hline

I'm basically trying to get horizontal lines at the top, bottom and after every row, so that it ends up looking like this (done using manual search and replace as a proof of concept):

Is this possible?

Answer 1

The tabular environment defines tabularnewline to some appropriate value when the environment starts, so if you try to define it beforehand it will get overridden when the environment starts anyway.

This is doing literally what the OP asks for (without regarding whether it's a good idea or not), replacing each tabularnewline with \\ \hline. (note that then the middle rule and the bottomrule get duplicated. It's the readers's exercise to handle them.)

Remark

• \__a violates expl3's naming style. Fix yourself if you want.
• Documentation can be found in texdoc interface3 / texdoc xparse
• Synctex is lost, and verbatim cannot be used inside the environment. These can be fixed, but it's a bit difficult.
• For simplicity, the environment grabs the initial om arguments inside the #1. It doesn't really matter in this case, but watch out if you modify the code.

%! TEX program = lualatex
\documentclass[oneside,a4paper]{book}

\usepackage{longtable}
\usepackage{tablefootnote}
\usepackage{booktabs}

\ExplSyntaxOn

% ======== backup the old environment
\let    \oldlongtable    \longtable
\let \endoldlongtable \endlongtable


% ======== override it
\RenewDocumentEnvironment {longtable} {+b} {
  \tl_set:Nn \__a {#1}
  \regex_replace_all:nnN {\c{tabularnewline}} {\c{ \\ }\c{hline}} \__a
  \exp_args:NV \__printtable:n \__a
}{}

\cs_set_protected:Npn \__printtable:n #1 {
  \begin{oldlongtable} #1 \end{oldlongtable}
}


\ExplSyntaxOff


\begin{document}

\begin{longtable}[]{@{}ll@{}}
\toprule
\begin{minipage}[b]{0.29\columnwidth} Value\strut \end{minipage} & \begin{minipage}[b]{0.65\columnwidth} Description\strut \end{minipage}\tabularnewline
\midrule
\endhead
\begin{minipage}[t]{0.29\columnwidth} \textbf{Value 1}\strut \end{minipage} & \begin{minipage}[t]{0.65\columnwidth} Some details for 1\strut \end{minipage}\tabularnewline
\begin{minipage}[t]{0.29\columnwidth} \textbf{Value 2}\strut \end{minipage} & \begin{minipage}[t]{0.65\columnwidth} Some details for 2\strut \end{minipage}\tabularnewline
\bottomrule
\end{longtable}
\end{document}

Answer 2

I would not experimenting what you try to do. Better and far more simple is use tabularray package. Using it your code will become very short and clear:

\documentclass{article}
\usepackage{tabularray}



\begin{document}
\begin{longtblr}[
caption = Table title
                ]{hline{1,Z}=0.8pt, hline{2}=0.4pt, hline{3-Z}=solid,
                 colspec = {@{} X[0.3,l, font=\bfseries]X[0.7,c] @{}},
                 row{1}={font=\bfseries},
                 rowhead=1
                 }
Value   &   Description             \\
Value 1 &   Some details for 1      \\
Value 2 &   Some details for 2      \\
Value 3 &   Some details for 3      \\
Value 4 &   Some details for 4      \\
\end{longtblr}
\end{document}

However, I would not draw lines after each row. Also is not clear, if texts in the second column cells have only one line. Ih have more, than centering it may not be the best choice. For example:

\documentclass{article}
\usepackage{tabularray}

\usepackage{lipsum}


\begin{document}
\begin{longtblr}[
caption = Table title
                ]{hline{1,Z}=0.8pt, hline{2}=0.4pt, 
                 colspec = {@{} X[0.3,l, font=\bfseries]X[0.7,j] @{}},
                 row{1}={font=\bfseries},
                 row{2-Y}={rowsep=3pt},
                 rowhead=1
                 }
Value   &   Description     \\
Value 1 &   \lipsum[1]     \\
Value 2 &   \lipsum[2]     \\
Value 3 &   \lipsum[11]     \\
Value 4 &   \lipsum[66]     \\
\end{longtblr}
\end{document}

looks nice regardless that text in the second column is not centered.