Dotted vertical line in math array + siunitx?

Question

This works until I uncomment siunitx. I presume this is a bug? Should I file anywhere?

\documentclass{article}

\usepackage{amsmath}
\usepackage{arydshln}
\usepackage{mathtools}

% Uncommenting this line breaks this document. It will trigger a compilation error on the dotted line indicator.
%\usepackage{siunitx}

\begin{document}

\[
    \begin{array}{c : c : c}
        1 & 2 & 3 \\
        4 & 5 & 6 \\
    \end{array}
\]

\end{document}

Answer 1

The siunitx package loads array, part of the standard tools bundle for LaTeX (this is needed to allow the S and s column types to work). However, both array and arydshln make changes to the standard tabular mechanism and I suspect do no tests for other redefinitions. Thus you need to load array before arydshln:

\documentclass{article}

\usepackage{array}
\usepackage{arydshln}
\usepackage{siunitx}

\begin{document}

\[
    \begin{array}{c : c : c : S}
        1 & 2 & 3 & 12.3\\
        4 & 5 & 6 & 4.56\\
    \end{array}
\]

\end{document}

(S column added to show that things still work properly.)