# How to pass style options to \pgfextra nodes

According to this answer, I created a style for drawing rectangles with double lines. The problem is, if I pass options like fill=color or thick to the node which I create with the style, these options are obviously not passed to the outer node, so the outer node won't be drawn correctly. (See MWE)

Remark: I can't use the double key, as I normally want the gap between the two lines to be transparent. This is why I use the method of the answer I linked.

So the question is, is there a way to pass the options of the style (nonlin) to the \pgfextra or to extract the properties of the \tikzlastnode and reuse it then? Why do I need to use \pgfextra here anyway? Or am I just overseeing a trivial solution? Notice the wrong line width of the outer node and the wrong filling of the gap of the first node:

\documentclass[border=2pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{backgrounds,fit, positioning}

\tikzset{
nonlin/.style = {
rectangle,thick,draw,minimum width=1cm,minimum height=0.6cm,
append after command={
\pgfextra{
\node[fit=(\tikzlastnode), draw, inner sep=1.8pt] (\tikzlastnode-outer) {};
}
}
}
}

\begin{document}
\begin{tikzpicture}
\node(mynode)[nonlin,fill=blue!20]at(0,0){$a$};
\node(node2)[nonlin, right=of mynode]{$b$};
\begin{scope}[on background layer]
\node[fit=(mynode)(node2), inner sep=5pt,fill=gray!30]{};
\end{scope}
\draw[->,thick](mynode-outer)--(node2-outer);
\end{tikzpicture}
\end{document}

• I'm not really sure what you're trying to accomplish here. Do you just want a fill directive to get shard by a family of nodes? Perhaps if you could clarify what kind of behavior your looking for we could help. But right now, I'm not sure how you want things to behave. Jan 28 '16 at 18:42
• I'm sorry if I'm unclear. I'm creating the outer node by the nonlin style. What I want to achieve is that if I pass further options to the (inner) node like for example thick or fill=color, then I want the outer node to also have these styles. More clear now? (Sorry, I'm not able to insert the ' signs for code on mobile device...) Jan 28 '16 at 18:54

Is this what you wanted?

\documentclass[border=2pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{backgrounds,fit, positioning}

\tikzset{
nonlin/.style = {
rectangle,thick,draw,minimum width=1cm,minimum height=0.6cm,#1,
append after command={
\pgfextra{
\node[fit=(\tikzlastnode),#1, draw, inner sep=1.8pt] (\tikzlastnode-outer) {};
}
}
}
}

\begin{document}

\begin{tikzpicture}

\node[nonlin={fill=blue!20}]     (mynode) at (0,0) {$a$};
\node[nonlin, right=of mynode] (node2)           {$b$};

\begin{scope}[on background layer]
\node[fit=(mynode)(node2), inner sep=5pt,fill=gray!30]{};
\end{scope}

\draw[->,thick](mynode-outer)--(node2-outer);

\end{tikzpicture}

\end{document}


• Thanks, this is a good solution. Still, I was hoping to find a way in which I don't have to pass the arguments by nonlin={...}... Why? Lets say for example I have a scope in which I want to change the background (or a different style) of all nonlin blocks. Then it would be nice to simply write nonlin/.append style={fill=white} or so. How could I achieve this here? Jan 29 '16 at 6:29