Macro inside TikZ node properties

Question

I was looking for a way to use a conditional expression to define the node type in TikZ. Specifically, I wanted to do something based on the section number.

 \def\checksectionshape#1{\ifthenelse{\value{section}=#1}{typea}{typeb}}
 ...
 \begin{tikzpicture}
 \node[\checksectionshape{1}] at (0,0) {Test};
 \end{tikzpicture}

From some of the similar questions and their, I guess this is because the \ifthenelse part is probably not expanded when the macro is called. But I couldn't manage to get one of those answers to work for my case.

Is there a workaround?

Answer 1

I suspect that this is due to expansion. Generally, I would avoid requiring expansion in the actual arguments to a \node or other TikZ path component. However, it is easy to shift the expansion one layer out where it works fine. This is done using a key. The key executes some code which sets the shape accordingly.

\documentclass{article}
\usepackage{ifthen}
\usepackage{tikz}

\tikzset{
  check section shape/.code={
    \ifthenelse{\value{section}=#1}{%
      \tikzset{rectangle}%
    }{%
      \tikzset{circle}%
    }
  }
}

\begin{document}
\section{Introduction}
\begin{tikzpicture}
\node[check section shape=1,draw] at (0,0) {Section 1};
\node[check section shape=2,draw] at (3,0) {Section 2};
\end{tikzpicture}
\section{Main Part}
\begin{tikzpicture}
\node[check section shape=1,draw] at (0,0) {Section 1};
\node[check section shape=2,draw] at (3,0) {Section 2};
\end{tikzpicture}
\end{document}

This produces: