nicematrix set name by pgfkey - expanding problem?

Question

Once again I need help with my gaussenv macro. This time, since the names of the pictures drawn by nicematrix have to be different. Therefore, I thought I'd create a numeric pgfkey which holds some kind of index of the current matrix.

And this is with which I came up:

\documentclass{article}

\usepackage{nicematrix}
\usepackage{tikz}
\usetikzlibrary{calc}

\pgfkeys{
        /tikz/gaussenv/.cd,
        niceMatrixName/.initial=1,
}

\begin{document}
\pgfkeysvalueof{/tikz/gaussenv/niceMatrixName}matrix

\begin{align*}
        \begin{pNiceMatrix}[name={\pgfkeysvalueof{/tikz/gaussenv/niceMatrixName} matrix}]
                1 & 1 & 1 & 1 \\
                2 & 2 & 2 & 2 \\
                3 & 3 & 3 & 3 \\
        \end{pNiceMatrix}
\end{align*}

\begin{tikzpicture}[remember picture,overlay]
        \draw (1 matrix-1-1) -- (1 matrix-2-2);
\end{tikzpicture}

\end{document}

But sadly when compiling tikz does not know the nodes 1 matrix-1-1 or 1 matrix-2-2, but if I use \begin{pNiceMatrix}[name={1 matrix}] as environment declaration, if works.

I guess it has something to do with expanding, but I don't know how to solve this and even if it is really because of expanding.

Can someone help me?

Answer 1

Instead of giving a name to each environment of nicematrix, you should access to the PGF/Tikz nodes created by nicematrix directly by their names. These names use the number of the environment given by \NiceMatrixLastEnv (available in versions ≥ 3.9 2020-01-10).

\documentclass{article}

\usepackage{nicematrix}
\usepackage{tikz}

\begin{document}

\begin{align*}
        \begin{pNiceMatrix}
                1 & 1 & 1 & 1 \\
                2 & 2 & 2 & 2 \\
                3 & 3 & 3 & 3 \\
        \end{pNiceMatrix}
\end{align*}
\begin{tikzpicture}[remember picture,overlay,name prefix = nm-\NiceMatrixLastEnv-]
  \draw (1-1) -- (2-2);
\end{tikzpicture}

\end{document}