How bad is slack \makeatother discipline really?

Question

Following Will Robertson's admission that Fwiw, i'm not aware of any troubles with a missing \makeatother, but you're right. It's a bad habit of mine to omit it, and my own progressive slackness about the same thing following my realisation that I never see it matter, I wonder how important the \makeatother discipline is?

The worst consequence I can think of for experienced users from slackness about closing with \makeatother is that one's slackness might spread to omitting \ExplSyntaxOff with expl3, which is very far from trouble-free. But that's not a mistake anyone is going to get used to making.

The insidious worry is that not following the discipline means that some people might become unclear about the distinction between "package/Knuth namespace" and "user namespace".

But I can't say that either of these considerations seems very urgent. It doesn't seem important in the same way as such a programmatic discipline as eliminating avoidable state in interfaces. Is there something more compelling?

Answer 1

In theory it would be possible that there is a @ direct after a macro in the users document or in one of the auxiliary files. Without the \makeatother this would cause trouble.

A second source of trouble are special packages which read user input and compare them using \let/\futurelet and \ifx. I'm not sure how the array package parses a potential @ in the column definition of tabular, but e.g. my tikz-timing package allows @{<code>} sequences and I was wise enough to test for @ with catcode letter and other. If I wouldn't have thought of that a missing \makeatother would break certain user code without much idea why.

In general it is good programming practice to close everything you open explicitly by yourself. This can be \makeatletter/\makeatother or \openout/\closeout or anything like it. This doesn't apply when the change was localized using a group.

Answer 2

A problem with slack \makeatother discipline is that it clashes with the use of \@ to reset the space factor after non-sentence-ending periods.

\documentclass{article}
\begin{document}
Articles from the Proc. Amer. Math. Soc.

Articles from the Proc.\@ Amer.\@ Math.\@ Soc.

\makeatletter
Articles from the Proc.\@ Amer.\@ Math.\@ Soc.
\end{document}