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In tikz, the macro \draw accept a optical argument of parameters separated with comma, e.g.

\draw[->, red] (0, 0) -- (1, 1)

I have a self defined macro, in which I want to pass a macro as this optional parameter, i.e. sth like

\def\p{->, red} \draw[\p] (0, 0) -- (1, 1)

However, I get a ERROR: Package pgf Error: Arrow end type ``>, red'' unknown. which is the same error with

\draw[{{->, red}}] (0, 0) -- (1, 1)

I think it is because the argument is passed as a single character and failed to be separated.

Is there a way to do it correctly? (i.e. "unquote" the curly bracket before passing it to the \draw macro.)

In my particular case, I use xkeyval package to define my macro according to this. Therefore I have to pass the argument through a macro.

(Any tikz specific work around is also helpful. THX)

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  • THX, all the solutions works for me. I have chosen the answer that is the best for my case, although other answers were actually what I was planning to look for. =D Commented Mar 27, 2012 at 22:08

3 Answers 3

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You should use \tikzset{MyStyle/.style={->, red}} instead of a \def to define your own custom style to be applied:

\documentclass{article} \usepackage{tikz} \tikzset{MyStyle/.style={->, red}} \begin{document} \begin{tikzpicture} \draw[MyStyle] (0, 0) -- (1, 1); \end{tikzpicture} \end{document}
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\documentclass[11pt]{scrartcl} \usepackage{tikz} \begin{document} \begin{tikzpicture} \def\p{->, red} \draw\expandafter[\p] (0, 0) -- (1, 1); \end{tikzpicture} \end{document}

or with etex

\begin{tikzpicture} \def\p{->, red} \makeatletter \protected@edef\tmp{% \noexpand \draw[\p] (0, 0) -- (1, 1);}\tmp \end{tikzpicture}
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  • I guess that defining a new arrow style might be better. Commented Mar 27, 2012 at 21:53
  • @egreg I agree with you but \protected@edef\tmp{ saves me in a lot of painful situations and if OP writes a package it's perhaps very useful. Commented Mar 27, 2012 at 22:00
  • Oh, yes: I've suggested a few times something of the kind. Commented Mar 27, 2012 at 22:02
  • @egreg It's difficult to understand that OP wants to use tikz with a macro and he doesn't know what is a style ! Commented Mar 27, 2012 at 22:16
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An immediate solution to your problem is 

\expandafter\draw\expandafter[\p]

But if you want to use this systematically, it will become awkward.

Anyway, whatever you do you need to make sure the content of [] is expanded before \draw is executed.

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  • Yes, this (order of expansion) is what I was confusing about. THX. Commented Mar 27, 2012 at 22:09

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