Conditionally execute a macro depending on the font used

I’m a big fan of ampersands – so much that I heed SimpleBits’ advice to “use the best available ampersand” quite religiously.

For that purpose, I’ve defined the following shortcut in LaTeX:

\let\amp\&
\renewcommand\&{{\scalebox{1.2}{\textnormal{\fontspec{Baskerville}\itshape\amp}}}}

In brief, this changes all uses of the “normal” ampersand to a stylish variant, e.g.:

This is a text \& it contains an ampersand.

(Using \& instead of just & since that’s how LaTeX works – the latter is already reserved to separate columns in table environments.)

However, this always uses the same font – here, Baskerville – no matter whether it fits or not. I’d like to use a different font depending on the font family used. That is, I want to use another ampersand in combination with sans serif text, and in particular I want to prevent rewriting of the ampersand in a monospace context. So in the following two contexts, I don’t want to trigger the above definition:

{\sffamily a \& b}
{\ttfamily a \& b}

How do I do that?

I imagine something like the following:

\renewcommand\&{
  \ifsans
    {\fontspec{Trebuchet MS}{\textnormal{\itshape\amp}}}
  \else
    \ifmono
      \amp
    \else
      {\fontspec{Baskerville}\scalebox{1.2}{\textnormal{\itshape\amp}}}
    \fi
  \fi}

Solution

It works the following way:

\documentclass[letterpaper,10pt]{article}
\usepackage[latin1]{inputenc}
\usepackage{german}
\usepackage{geometry}
\geometry{margin=2cm}
\newcommand*\origsffamily{}
\let\origsffamily\sffamily
\renewcommand*\sffamily{\origsffamily\small {\renewcommand\&{{\scalebox{1.2}{\textnormal{\fontspec{Baskerville}\itshape\amp}}}}}}

\begin{document}


hello, this is \& a \sffamily test \& 


\end{document}

That means, you include the change of the ampersand sign into the definition of (in my example) \sffamily.

The drawback is - of course - that you have to do this for all desired font families.