Why does \insertauthor lead to an error inside \ifthenelse statement?

Question

Using \insertauthor in \ifthenelse statement throws an error (no error if it is used elsewhere in the document). \inserttitle or \insertdate works fine. Why do I get an error when I use \insertauthor as below? You can see that I am trying to check if author information is provided.

\documentclass{beamer}
\usepackage{ifthen}

%\title{Title goes here}
\author{me}

\begin{document}

\ifthenelse{\equal{\insertauthor}{}}{empty}{not empty}

\end{document}

Answer 1

The \insertauthor macro does more than just inserting the author, so you run into a problem with exandability.

Instead you can check if \beamer@shortauthor or \beamer@andstripped is empty or not (the result will be different for the case \author[]{me}, not sure which behaviour you would like).

I also included a second approach which is used in beamer to test e.g. in footlines if certain information is available

\documentclass{beamer}
\usepackage{ifthen}

\author{me}

\makeatletter
\newcommand{\fooooo}{\ifthenelse{\equal{\beamer@shortauthor}{}}{empty}{not empty}}

\newcommand{\foo}{\expandafter\ifblank\expandafter{\beamer@shortauthor}{empty}{not empty}}
\makeatother

\begin{document}
\begin{frame}
\fooooo

\foo
\end{frame}
\end{document}