How to redefine several commands all at once?

Question

It happens sometimes that because I deal with complicated formulas, I want to add extra space around certain symbols, e.g. \longrightarrow, \subset, \cong, etc.

Here is a MWE:

\documentclass{article}
\usepackage{ifthen}

\let\OLDsubset\subset
\renewcommand{\subset}[1][0]{
    \ifthenelse{\equal{#1}{0}}{\OLDsubset}{}
    \ifthenelse{\equal{#1}{1}}{\;\OLDsubset\;}{}
    \ifthenelse{\equal{#1}{2}}{\;\;\OLDsubset\;\;}{}
    \ifthenelse{\equal{#1}{3}}{\quad\OLDsubset\quad}{}
}

\begin{document}
$$A \subset B$$
$$A \subset[2] B$$
\end{document}

It works well, but my question is the following. Is there a way to create a single 'meta-command' (macro) e.g. \AddSpace that takes a command as argument, and then for instance \AddSpace{\subset} would produce the above code automatically.

The goal is to be able to use the same code as above for other commands as \subseteq, \cong (that do not initially take optional arguments, for safety), etc., without having to copy-paste the same piece of code for each of those commands.

I am aware of multidef package, but it doesn't seem to be the right tool here. I tried to play around the ideas from here, without much success. Maybe with xparse package, and \RenewDocumentCommand, etc.?

---

NB: I do not want to have something like this:

\newcommand{\AddMoreSpace}[2][1]{
    \ifthenelse{\equal{#1}{1}}{\;#2\;}{}
    \ifthenelse{\equal{#1}{2}}{\;\;#2\;\;}{}
    \ifthenelse{\equal{#1}{3}}{\quad #2 \quad}{}
}

because using e.g.

$$A \AddMoreSpace{\subset} B$$
$$A \AddMoreSpace[2]{\subset} B$$

is too "complicated" / too long to write...

Answer 1

The command \; is shorthand for \mskip\thickmuskip, so you can multiply it, instead of adding.

The old command name is saved as \watson<oldcommand using a \csname trick.

\documentclass{article}
\usepackage{amsmath}

\newcommand{\AddSpaceToCommand}[1]{%
  \expandafter\NewCommandCopy\csname watson\string#1\endcsname #1%
  \renewcommand#1[1][0]{%
    \mspace{\muexpr\thickmuskip*##1\relax}%
    \csname watson\string#1\endcsname
    \mspace{\muexpr\thickmuskip*##1\relax}%
  }%
}

\AddSpaceToCommand{\subset}
\AddSpaceToCommand{\mapsto}

\begin{document}

$a \subset b$

$a \subset[1] b$

$a \subset[2] b$

$a \subset[3] b$

$a \mapsto b$

$a \mapsto[1] b$

$a \mapsto[2] b$

$a \mapsto[3] b$

\end{document}

Answer 2

After searching quite a bit, I finally found a way to solve my problem. Any comment is welcome -- the following MWE might show some "bad practice" (but at least it works!)...

\documentclass{article}
\usepackage{ifthen}

\newcommand{\AddSpace}[1]{
    \expandafter\let\csname old#1\expandafter\endcsname\csname#1\endcsname
    \expandafter\renewcommand\csname #1\endcsname[1][0]{%
        \ifthenelse{\equal{##1}{0}}{\csname old#1\endcsname}{}%
        \ifthenelse{\equal{##1}{1}}{\;\csname old#1\endcsname\;}{}%
        \ifthenelse{\equal{##1}{2}}{\;\;\csname old#1\endcsname\;\;}{}%
        \ifthenelse{\equal{##1}{3}}{\quad\csname old#1\endcsname\quad}{}%       
    }%
}

\AddSpace{subset}
\AddSpace{mapsto}


\begin{document}

$a \subset[3] b$

$a \subset b$

$a \mapsto[2] b$

$a \mapsto b$

\end{document}