How to create something like a function (procedure, macros, etc.) in TikZ?

Question

I want to draw this thing many a time:

\node[circle,draw,thick,inner sep=0pt,minimum size=2ex] (sum) [left = of myobject] {};
\draw[semithick] (sum.north west) -- (sum.south east);
\draw[semithick] (sum.south west) -- (sum.north east);
\fill (sum.center) -- (sum.south west) arc (-135:-45:1ex) -- cycle;

Is it possible to make a one command that will execute all this code? And [left = of myobject] should be a variable.

Answer 1

New TiKZ 3.0 pics can help you:

\documentclass[tikz,border=2mm]{standalone}
\usetikzlibrary{positioning}

\tikzset{mysymbol/.pic={
    \node[circle,draw,thick,inner sep=0pt, minimum size=2ex] (-sum) {};
    \draw[semithick] (-sum.north west)--(-sum.south east);
    \draw[semithick] (-sum.south west)--(-sum.north east);
    \fill (-sum.center)--(-sum.south west) arc (-135:-35):1ex)--cycle;
}}

\begin{document}
\begin{tikzpicture}

\node (a) {A};

\path pic (symbol_a) at ([xshift=1cm]a) {mysymbol};

\pic[above right=5mm and 8mm of a, red] (symbol_b) {mysymbol};

\pic[left=of symbol_b-sum, blue] {mysymbol};
\end{tikzpicture}

\end{document}

Some pic examples here:

• How can I draw a TikZ element multiple times against a shaded background?
• How can I rotate and mirror a tikz picture in latex

Update: Include filled sectors as parameter

Next code show one possibility of including which sectors will be filled as a parameter to the pic definition.

To use parameters with a pic a new syntax is needed, the original mysymbol/.pic changes to pics/mysymbol/.style={code={.... This is enough with only one parameters but it's also possible to use 2 (pics/mysymbol/.style 2 args={code={...) or more (pics/mysymbol/.style n args={n}{code={...). Take a look at TikZ 3.0---Multiple arguments for `pic` for some other examples.

In this case you can pass a sector list (from 0 to 3, 0=east sector, 1=north, ...).

\documentclass[tikz,border=2mm]{standalone}
\usetikzlibrary{positioning}

\tikzset{
    pics/mysymbol/.style={
        code={
    \node[circle,draw,thick,inner sep=0pt, minimum size=2ex] (-sum) {};
    \draw[semithick] (-sum.north west)--(-sum.south east);
    \draw[semithick] (-sum.south west)--(-sum.north east);
    \foreach \i in {#1}
    \fill[rotate=90*\i] (-sum.center)--++(-45:1ex) arc[start angle=-45,delta angle=90,radius=1ex]--cycle;
}}} 

\begin{document}
\begin{tikzpicture}
\node (a) {A};

\path pic (symbol_a) at ([xshift=1cm]a) {mysymbol={2,0}};

\pic[above right=5mm and 8mm of a, red] (symbol_b) {mysymbol={0}};

\pic[left=of symbol_b-sum, blue] {mysymbol={0,2,3}};
\end{tikzpicture}

\end{document}

Answer 2

Based on your question, [left = of myobject] is translated into 3 arguments [#1 = #2 of #3]

The user-defined command mydraw is to draw the repeated lines, which takes a style mylocation that takes #1 = above, below, left or right, #2 = x unit and #3 = myobject. Here A=myobject in this example.

Code

\documentclass[border=10pt]{standalone}
%\usepackage[margin=1cm]{geometry}
\usepackage{tikz}
\usetikzlibrary{calc,positioning}

\tikzset{mylocation/.style args={#1 and  #2 of #3}{
#1 = #2 of #3}
}

\newcommand\mydraw[3]{
\node[circle,draw,thick,inner sep=0pt,minimum size=2ex] (sum) [mylocation= #1 and #2 of #3] {};
\draw[semithick] (sum.north west) -- (sum.south east);
\draw[semithick] (sum.south west) -- (sum.north east);
\fill (sum.center) -- (sum.south west) arc (-135:-45:1ex) -- cycle;
}


\begin{document}
\begin{tikzpicture}
\node(A) at (0,0) {A};

\mydraw{above}{2}{A}
\mydraw{left}{2}{A}
\mydraw{right}{2}{A}
\mydraw{below}{2}{A}
\end{tikzpicture}
\end{document}