Define first row color prior to tabular begin

Question

I've got many tables throughout my document that I would like to be colored like this, with the first row in a dark grey, then the even rows in white and the odd rows in a light grey:

Currently I'm using this to achieve this:

\usepackage[table]{xcolor}
\rowcolors{2}{white}{gray!15}

\begin{tabularx}{cX}
\rowcolor{gray!50}
Row Number & Text \\
\hline
\therownum & test \\
\therownum & test \\
\therownum & test \\
\therownum & test \\
\therownum & test \\
\therownum & test \\
\end{tabularx}

I'm looking for a way to avoid having to call \rowcolors and \hline with every tabularx begin. Is there a way to do this while keeping a variable number of columns?

An interface of something like this would be ideal:

\begin{something}{cc}
Row Number & Text \\
\therownum & test \\
\therownum & test \\
\therownum & test \\
\therownum & test \\
\therownum & test \\
\therownum & test \\
\end{something}

Answer 1

A solution with {NiceTabular} of nicematrix.

\documentclass{article} 
\usepackage{nicematrix}

\def\therownum{\arabic{iRow}}

\NewDocumentEnvironment{MyTable}{m}
  {
   \begin{NiceTabular}{#1}
   \CodeBefore
      \rowcolor{gray!50}{1}
      \rowcolors{3}{gray!15}{}
   \Body
  }
  {\end{NiceTabular}}

\begin{document}

\begin{MyTable}{cc}
Row Number & Text \\
\therownum & test \\
\therownum & test \\
\therownum & test \\
\therownum & test \\
\therownum & test \\
\therownum & test \\
\end{MyTable}

\end{document}