Inspecting code of a package I saw the following two lines:
\def\th{\textormath{\text@th}{\math@th}}
and
\ifmmode{\nfss@text{\textnumero}}\else\textnumero\fi}
I guess that textormath and \ifmmode do basically the same: they print either their first or their second argument depending on whether math or text mode is active. But what is the difference between these two commands? And which one is preferable?
The latex format defines \TextorMath which is a very thin wrapper around \ifmmode You don't say what defined \textormath but it is presumably similar.
\begingroup\expandafter\expandafter\expandafter\endgroup
\expandafter\ifx\csname protected\endcsname\relax
\DeclareRobustCommand\TextOrMath{%
\ifmmode \expandafter\@secondoftwo
\else \expandafter\@firstoftwo \fi}
\protected@edef\TextOrMath#1#2{\TextOrMath{#1}{#2}}
\else
\protected\expandafter\def\csname TextOrMath\space\endcsname{%
\ifmmode \expandafter\@secondoftwo
\else \expandafter\@firstoftwo \fi}
\edef\TextOrMath#1#2{%
\expandafter\noexpand\csname TextOrMath\space\endcsname
{#1}{#2}}
\fi
In general it's better to use the latex form unless you know the context and it it is safe to use the TeX primitive, notably in section headings and at the start of table cells \ifmmode acts in a well defined way but not as you may expect and not usefully, (it is always false at the start of an array cell for example)
\documentclass{article}
\begin{document}
$
\begin{array}{c}
\ifmmode math \else text\fi \\
{}\ifmmode math \else text\fi \\
\TextOrMath{text}{math} \\
{}\TextOrMath{text}{math} \\
\end{array}
$
\end{document}
The (lowercase) macro \textormath is defined in babel.def and provides a wrapper to the \ifmmode macro:
\def\textormath{%
\ifmmode
\expandafter\@secondoftwo
\else
\expandafter\@firstoftwo
\fi}
As such, it will have the same problems as a direct use of \ifmmode e.g. at the beginning of a cell (see David's answer).
\relax in there,
– David Carlisle
Aug 11 '17 at 16:10
\TextOrMath was added to LaTeX in 2005, first as part of the fixltx2e package (see ltnews.pdf, issue 17). I think it's possible that babel's \textormath command predates that. You might argue that these days, they should just \let\textormath=\TextOrMath.
– Harald Hanche-Olsen
Aug 12 '17 at 10:04
}in your\ifmmodeexample, note that it doesn't take brace arguments but\ifmmode yes \else no \fi– David Carlisle Aug 11 '17 at 15:50t1enc.def), whereas the second may work wrongly inarray(it should have\relax\ifmmode). – egreg Aug 11 '17 at 16:18