Text Formatting ⇒ double quotes in monospace with acm_proc_article-sp

[user49915]

Consider the input

\documentclass{acm_proc_article-sp}
\begin{document}
\texttt{``foo''}
\end{document}

using the most recent acm_proc_article-sp.cls, which I believe to be version 3.2 and which you can take, e.g., from https://raw.githubusercontent.com/tewal ... cle-sp.cls.

In the output

mwe.jpg (5.43 KiB) Viewed 1798 times

the quotes are missing, which is n.f.g. Of course, we can get the double quotes in this particular case as ", though I think it is generally discouraged. Now, I wonder:

• Why do we get black boxes instead of anything meaningful,

• what's the proper™ way to get opening and closing doubles quotes,

• what's the proper™ way to get opening and closing single quotes, and

• what's the proper™ way to get straight double quotes

in the scope of \texttt{...} using that old class?