How do I make a parameter optional for a Tikz library?

Question

I am making a tikz library and I would like to use an optional parameter. So far, I have the following code

The tikzlibraryquestion.code.tex file is

\usepackage{question}

\tikzset{
 question/.pic={
   \question@draw
  },
}

There is a question.sty file

\ProvidesPackage{question}

\RequirePackage{tikz}


\newcommand*{\mycircle}[1][]{
    \tikzset{%
        /mycircle/.cd,#1}\mycircle@draw%
}

\tikzset{
    /mycircle/.cd,
    /mycircle/tilt/.code = 0    \def\mycircle@tilt{#1},
}

\def\mycircle@draw{
    \draw (0, 0) circle (1);
    \begin{scope}[rotate=\mycircle@tilt]
         \draw (0, 0) -- (0, 1);
    \end{scope}
}

Finally, the example of use

\documentclass{standalone}

\usepackage{tikz}
\usetikzlibrary{question}

\begin{document}
\begin{tikzpicture}
\mycircle[tilt=23]
\end{tikzpicture}

\begin{tikzpicture}
\mycircle
\end{tikzpicture}
\end{document}

How do I change the .sty file so that the tilt parameter be optional ?

Answer 1

You could just use a pic. pics are made for this.

\documentclass{standalone}
% you can put the following three lines in a package, of course
\usepackage{tikz}
\tikzset{pics/my circle/.style={code={
        \draw (0,1) -- (0, 0) circle [radius=1];}}}
\begin{document}
\begin{tikzpicture}
\pic[rotate=23]{my circle};
\end{tikzpicture}

\begin{tikzpicture}
\pic{my circle};
\end{tikzpicture}

\begin{tikzpicture}
\pic[red,dashed,scale=2,rotate=-33]{my circle};
\end{tikzpicture}
\end{document}

As you can see, you can add as many optional parameters as you wish.

For more advanced options, use pgf keys. Example:

\documentclass{standalone}
% you can put the following three lines in a package, of course
\usepackage{tikz}
\tikzset{pics/my circle/.style={code={%
        \tikzset{my circle/.cd,#1}%
        \def\pv##1{\pgfkeysvalueof{/tikz/my circle/##1}}%
        \draw[pic actions,my circle/line] (0,1) -- (0, 0);
        \draw[pic actions,my circle/circle] (0,0) circle [radius=1];}},
        my circle/.cd,line/.style={},circle/.style={}}
\begin{document}
\begin{tikzpicture}
\pic[rotate=23]{my circle};
\end{tikzpicture}

\begin{tikzpicture}
\pic{my circle={line/.style={dashed,thick,blue}}};
\end{tikzpicture}


\begin{tikzpicture}
\pic[rotate=123,red] {my circle={line/.style={dashed,thick,blue}}};
\end{tikzpicture}

\begin{tikzpicture}
\pic[red,dashed,scale=2,rotate=-33]{my circle};
\end{tikzpicture}
\end{document}