Command macro for an environment

Question

How can I define a command macro using \newcommand so that the argument to the command is surrounded by an environment?

Answer 1

A proof that it is possible and using an optional argument that can be b or p or anything of the known prefixes (e.g. v, B and V)

Besides that all: It does not improve readability of the code, in my point of view.

\documentclass{article}

\usepackage{amsmath}

\newcommand{\mat}[2][b]{%
  \begin{#1matrix}
    #2
  \end{#1matrix}
}

\begin{document}
$\mat{ 1 & 2 \\ 3 & 4 \\}$ and $ \mat[p]{ 1 & 2 \\ 3 & 4 \\}$ and $\mat[B]{ 1 & 2 \\ 3 & 4 \\}$ and $\mat[v]{ 1 & 2 \\ 3 & 4 \\}$ and $ \mat[V]{ 1 & 2 \\ 3 & 4 \\}$
\end{document}