Minimal work example for darray from breqn

Question

I was trying to use the darray environment from the breqn package but hadn't success on it.

As a mwe I would like to replace the eqnarray below by the darray.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{eqnarray*}
  \max & & c^T x \\
  \text{s.t.} & & x \in \left\{ 0, 1 \right\}^n
\end{eqnarray*}
\end{document}

I try

\documentclass{article}
\usepackage{amsmath}
\usepackage{breqn}
\begin{document}
\begin{darray}[cols={rl}]
  \max & c^T x \\
  \text{s.t.} & x \in \left\{ 0, 1 \right\}^n
\end{darray}
\end{document}

but got the error below

! Undefined control sequence.
\@tempc ...let \@preamble \@empty \darray@mkpream 
                                                  #1\@percentchar 
l.5 \begin{darray}[cols={rl}]

? 
! Emergency stop.
\@tempc ...let \@preamble \@empty \darray@mkpream 
                                                  #1\@percentchar 
l.5 \begin{darray}[cols={rl}]

End of file on the terminal!

Answer 1

The breqn documentation specifies that "the darray environment is unfinished". Perhaps a safer alternative should be used. How about simply using an array environment?

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[
\begin{array}{rl}
  \max    &  c^T x \\
  \text{s.t.} & x \in \left\{ 0, 1 \right\}^n
\end{array}
\]
\end{document}

Answer 2

Same semantics, different syntax. Decide which you find easier to read.

\begin{equation*}
\max \left\{ c^T x \mid x \in \left\{ 0, 1 \right\}^n \right\}
\end{equation*}