Problem in definition of newcommand with optional argument

Question

I'm trying to define a newcommand in a .cls file as follows:

\newcommand{\test}[2][]{%
    \ifthenelse{\isempty{#1}}%
    {\raggedright\itshape{#2}}%
    {\raggedright#1 \hfill \itshape{#2}}%
}

However, this gives LaTeX Error: Something's wrong--perhaps a missing \item. I have included the package xifthen with \RequirePackage{xifthen}. I should also mention that if one removes the [], which is intended for the optional argument, the code seems to work just fine. What am I missing here?

EDIT: here's the main part of the class file:

\NeedsTeXFormat{LaTeX2e}
\ProvidesClass{my_class}[2020/07/31 My custom class]
\LoadClass{article}
\RequirePackage[T1]{fontenc}
\RequirePackage{xifthen}

\newenvironment{myenv}%
    {\addvspace{0.1in}\noindent\ignorespaces}
    {\par\noindent%\addvspace{0.1in}
    \ignorespacesafterend}

\newcommand{\first}[2]{%
    {\begingroup \raggedright \textbf{#1} \hfill \textit{#2} \newline \endgroup}%
}

\newcommand{\second}[2][]{%
    \ifthenelse{\isempty{#1}}%
    {\textit{\raggedleft #2} \newline}%
    {\begingroup \raggedright #1 \hfill \textit{#2} \newline \endgroup}%
}

and here's a minimal working example:

\documentclass{my_class}

\begin{document}

\section{First section}

\begin{myenv}
    \first{This is bold text}{This is italic text}
    \second[Optional argument given]{This is italic text}
\end{myenv}

\begin{myenv}
    \first{Bold text}{Italic text}
    \second{Optional argument omitted}
\end{myenv}

\end{document}

When \second is provided with the optional argument, it seems to work fine, outputting the first argument to the left and the second to the right of the same line. However, when the optional argument is not provided, the second argument is written as if were left-justified, not right-justified (which is what I want). I used groups to limit the the effects of the switches such as \raggedright but I don't think I did it right.

Answer 1

I'm not sure what's the aim of the code, but there are several things that are superfluous.

\documentclass{article}

\newenvironment{myenv}
    {\par\addvspace{0.1in}}
    {\par\addvspace{0.1in}}
\newcommand{\first}[2]{%
    {\raggedright\textbf{#1}\hfill\textit{#2}\par}%
}
\newcommand{\second}[2][]{%
    {\raggedright#1\hfill\textit{#2}\par}%
}

\begin{document}

\section{First section}

\begin{myenv}
    \first{This is bold text}{This is italic text}
    \second[Optional argument given]{This is italic text}
\end{myenv}

\begin{myenv}
    \first{Bold text}{Italic text}
    \second{Optional argument omitted}
\end{myenv}

\end{document}

Note that \newline is out of place and would produce warnings. However, your code doesn't show the mentioned error in my experiment.