Multiple nested \ifdefined statements

Question

I use the "variables" in my header and would like to shorten the code by combining \ifdefined\@@author and \ifdefined\@group. Searching the repository for "ifdefined multiple arguments" etc. didn't give a useful result. I experimented with ||, as from different programming languages, but you can imagine... :)

Is there no easier way to do that?

\rhead{\small\color{darkgray2}%
    \ifdefined\@@author%
        \@@author%
        \ifdefined\@group%
            , %
        \fi%
    \fi%
    \ifdefined\@group%
        \@group%
    \fi%
    \ifdefined\@@date%
        \linebreak\@@date%
    \fi%
}

Thanks.

Edit (MWE):

\LoadClass{article}
\newcommand\group[1]{\def\group{#1}}
\author{Me}
\group{Group}
\title{Work Hygiene and Safety}
\date{18th~September~2018}

\RequirePackage{fancyhdr}
\pagestyle{fancy}
\fancyhf{}% 

\makeatletter
\rhead{
    \ifdefined\@author%
        \@author%
        \ifdefined\group%
            , %
        \fi%
    \fi%
    \ifdefined\group%
        \group%
    \fi%
    \ifdefined\@date%
        \linebreak\@date%
    \fi%
}
\makeatother
\begin{document} 
Hello
\end{document}

Answer 1

The logic of all TeX primitive conditionals is the same: they are 'one shot' tests with no combining logic. There are a variety of 'wrappers' which provide such logic, most notable in etoolbox and expl3, which use a more 'LaTeX-like' syntax. At the primitive level, one can create combinations by using \ifnum or \ifodd, for example

\ifnum0%
  \ifdefined\@@author 1\fi
  \ifdefined\@group 1\fi
  >0 %
  % Code for 'at least one is true' case
\else
  % Code for 'neither is true' case
\fi

This uses the fact that TeX keeps expanding material in the number test until it finds a non-numeral, in particular a comparator here. So the two \ifdefined tests get converted into either a value or nothing at all.