Using math mode relation symbols in text mode with optimised spacing

Question

I'd like to have easy access to commonly used relation symbols in text mode, just as they are easily accessible in math mode. An important example is ⊕, or \oplus. I'd like to configure the control symbol \+ to use it:

\documentclass{article}
\usepackage{amsmath}
\NewDocumentCommand{\+}{}{\ensuremath{\oplus}}

\begin{document}
    \section{Upright}
    a \+ b\\ 
    $ \text{a} \oplus \text{b} $
        
    \section{Italics}
    \textit{a} \+ \textit{b}\\
    $a \oplus b$
\end{document}

While this works, I still need to optimise the spacing so that it matches, or is similar to, the spacing in math mode:

I've tried the following:

• changing the value of \mathsurround in the definition, i.e. \NewDocumentCommand{\+}{}{\mathsurround=0pt\ensuremath{\oplus}} (I believe this is already the default)
• using \mathrel around \oplus in the definition.

None of these approaches have worked. One additional idea I had was to access the \oplus symbol directly, but the Unicode symbol would not link to the math relation symbol in the font I use. Is there another way?

Answer 1

You can try:

\def\+{\leavevmode\unskip\hbox{${}\oplus{}$}\ignorespaces}

This ignores space before and after \+ and adds the spaces from math mode.

Answer 2

If you want math-mode typesetting, what you really want is to switch to math mode, but typeset the arguments as text. Both \textup and \texit work in math mode. You could also use \mathrm or \mathit.

\documentclass{article}
\usepackage{amsmath}

\newcommand\plusify[2]{\( \text{#1} \oplus \text{#2} \)}

\begin{document}
    \section{Upright}
    \( \textup{a} \oplus \textup{b} \)
    \plusify{a}{b}
    \( \text{a} \oplus \text{b} \)
    \(\mathrm{a} \oplus \mathrm{b} \)
        
    \section{Italics}
    \( \textit{a} \oplus \textit{b} \)
    \plusify{\itshape a}{\itshape b}
    \( a \oplus b \)
    \( \mathit{a} \oplus \mathit{b} \)
\end{document}