LaTeX \newcommand default argument: is empty?

Question

I'm trying to write a simple example command that prints nothing without an argument, but with an argument it surrounds it with something.

I've read that the default value should be \@empty and the simple \ifx\@empty#1 condition should do the job:

\newcommand{\optarg}[1][\@empty]{% \ifx\@empty#1  {}  \else  {(((#1)))}  \fi }  \optarg % (((empty))) \optarg{} % (((empty))) \optarg{test} % (((empty))) test 

The latter three commands all print the empty word for some reason, and I want the first two to print nothing and the last to print (((test))).

I'm using TeXLive/Ubuntu. An ideas?

Answer 1

Try the following test:

\documentclass{article}  \usepackage{xifthen}% provides \isempty test  \newcommand{\optarg}[1][]{%   \ifthenelse{\isempty{#1}}%     {}% if #1 is empty     {(((#1)))}% if #1 is not empty }  \begin{document}  Testing \verb|\optarg|: \optarg% prints nothing  Testing \verb|\optarg[]|: \optarg[]% prints nothing  Testing \verb|\optarg[test]|: \optarg[test]% prints (((test)))  \end{document} 

The xifthen package provides the \ifthenelse construct and the \isempty test.

Another option is to use the ifmtarg package (see the ifmtarg.sty file for the documentation).

Answer 2

Using the LaTeX3 xparse package:

\usepackage{xparse} \NewDocumentCommand\optarg{g}{%   \IfNoValueF{#1}{(((#1)))}% }