[Tex/LaTex] What does \nop mean and how to use it

Question

I wonder what does the \nop mean, and how does it work? I Googled it but couldn't find a good answer, for example, I found something like:

\newcommand{\nop}[1]{}

in my .tex file, so what does it mean?

Answer 1

In your example, \nop is defined to take a single argument and do nothing with it. As such, \nop literally translates to "perform no operation", or "gobble your argument". In fact, there exists a similar core macro \@gobble (and friends) which does exactly the same (from latex.ltx:

\long\def \@gobble #1{}
\long\def \@gobbletwo #1#2{}
\long\def \@gobblefour #1#2#3#4{}

The first gobbles a single argument, making \@gobble{<anything>} expand to nothing. The second gobbles two arguments, making \@gobbletwo{<anything>}{<anything>} expand to nothing, and so on.

What's the use case here? Well, perhaps you define a macro that writes something in the margin, like a "to do" note:

\newcommand{\mymacro}[1]{\marginpar{Do #1}}

Now, later in your production, you decide that this operation is no longer valid/useful. So, you can make \mymacro act like \nop and do nothing, which allows you to leave your code as-is:

\let\mymacro\nop

or, at definition in your preamble, change it to a no-op:

\newcommand{\mymacro}[1]{}