How can I use rotate inside a defined TikZ command?

Question

Here is a simple file defining a TikZ command with an input for drawing options. That input works for options such as dashed or dotted. But it ignores the rotate and scale options. It runs fine with them, but it runs just as if they were not there.

The actual diagrams I want to draw are much more complicated and would benefit if I could use rotate and scale options. Can I do that somehow?

\documentclass{amsart}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}
     \[\begin{tikzpicture}
    \def\line[#1](#2)% Syntax: [draw options] (lefthand endpoint
      {\node at (#2) (A) {$\bullet$};
      \node at ($(#2)+(1,0)$) (B) {$\bullet$};
      \draw[#1] (A) edge[] (B);}
    \line[rotate=30,dashed](0,0);
          \end{tikzpicture}\]
\end{document}

Answer 1

This is a very quick fix.

\documentclass{amsart}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}
     \[\begin{tikzpicture}
    \def\line[#1](#2)% Syntax: [draw options] (lefthand endpoint
      {\begin{scope}[#1]
      \node at (#2) (A) {$\bullet$};
      \node at ($(#2)+(1,0)$) (B) {$\bullet$};
      \draw (A) edge[] (B);
      \end{scope}}
    \line[rotate=30,dashed](0,0);
          \end{tikzpicture}\]
\end{document}

However, I'd recommend to use a \newcommand instead.

Answer 2

The main reason why rotate does not do anything here is that it should not do anything: you are asking for a line to be drawn between two explicit points (A) and (B), so there is nothing to rotate! Typical uses for rotate inside a tikz \draw command are when you have a decoration or border shape to rotate. If you want to draw a line of length one that can be rotated then you should not use explicit named coordinates. The code below produces,

which is what I think you want. Here is the code:

\documentclass{amsart}
\usepackage{tikz}
\usepackage{xparse}
\NewDocumentCommand\Line{ O{} r()}{% Syntax: [draw options] (lefthand endpoint
  \draw[#1] (#2) node{$\bullet$} -- ++(1,0);
}
\begin{document}
  \begin{center}
    \begin{tikzpicture}
        \Line[rotate=30,dashed](0,0);
        \Line(2,0);
        \Line[rotate=90, blue](2,0);
    \end{tikzpicture}
  \end{center}
\end{document}

I have used \NewDocumentCommand from the xparse package to define the \Line command (I didn't use \line because there is already a \line command in LaTeX), so that it takes one optional argument and a mandatory argument enclosed in brackets. The line is drawn using relative coordinates ++(1,0) for the second point, so there is no need for the tikz library calc or to define the coordinates (A) and (B). Finally, I have defined \Line outside of the tikzpicture environment so that you can use it in different tikzpicture environments.