Remove spaces from around a "dummy" macro

Question

In the following MWE (it's minimal, so not the original problem). As you can check there is one space on both sides of \mycommand. While I'm making the macro "dummy" for a specific use: can I remove one of the spaces if there would be two left?

\documentclass{article}

\DeclareRobustCommand\mycommand[1]{%
   \textbf{#1}%
}

\makeatletter
\newcommand\nobf[1]{%
    {\def\mycommand##1{}#1}}
\makeatother

\begin{document}

\def\abc{X \mycommand{Y} Z \mycommand{!}}

\abc

\nobf{\abc}

X Z

\abc

\end{document}

There is a doubled space between the first X Z pair:

Answer 1

The reason for the spaces stem from your spurious ones in your macro definition: A line break without % acts like a space. For more on this discussion, see What is the use of percent signs (%) at the end of lines?.

A far shorter definition of \nobf would be

\newcommand\nobf[1]{{\renewcommand{\mycommand}[1]{\leavevmode\unskip\ignorespaces}#1}}

Note that there's no line break, so the macro doesn't introduce any spurious spaces in the output. Also, redefining \mycommand is done inside a group, so there's no need to save and restore the macro. The redefinition removes any skip before it (via \unskip) as well as ignoring any following (via \ignorespaces).

\documentclass{article}

\DeclareRobustCommand\mycommand[1]{\textbf{#1}}

\makeatletter
\newcommand\nobf[1]{{\renewcommand{\mycommand}[1]{\leavevmode\unskip\ignorespaces}#1}}
\makeatother

\begin{document}

\def\abc{X \mycommand{Y} Z \mycommand{!}}

\abc

\nobf{\abc}

X Z

\abc

\end{document}

Answer 2

In latex internal code, any command that can be used in a paragraph, but provides no visible text, uses two internal commands: \@bsphack and @esphack. The first one tries to detect if a space preceded it and passes that information to the second. If the space was there \@esphack issues \ignorespaces. Thus:

\documentclass{article}
\DeclareRobustCommand\mycommand[1]{%
   \textbf{#1}}
\makeatletter
\newcommand\nobf[1]{% Use the "space hack"
    {\def\mycommand##1{\@bsphack\@esphack}#1}}
\makeatother
\begin{document}
\def\abc{X \mycommand{Y} Z}
\abc

\nobf{\abc}

\def\abc{X\mycommand{Y} Z}
\abc

\nobf{\abc}

\def\abc{X \mycommand{Y}Z}
\abc

\nobf{\abc}
\end{document}

Actually, in this resricted application, no internal commands are needed. In place of \def\mycommand##1{\@bsphack\@esphack}
one can use
\def\mycommand##1{\ifdim\lastskip>0pt \ignorespaces\fi}