listing pre- and postbeak gives error in beamer slide [duplicate]

Question

Following this answer, I've tried to embed a listing with long lines into a beamer frame.

I'd like to have a nice red arrow at the line break (as show here).

The parameters prebreak and postbreak give an error while compiling it. As a matter of fact, it's the \textcolor that gives the error.

Here is the adapted MWE :

\documentclass[xcolor={svgnames,usenames,dvipsnames,table}]{beamer}
\usepackage[utf8]{inputenc} 
\usepackage[T1]{fontenc}
\usepackage{amssymb}
\usepackage{listings}

\lstset{%
    xleftmargin=3.4pt,
    xrightmargin=3.4pt,
    %keepspaces=true,
    columns=fullflexible,   % Rasterize the columns
    frame=single,
    basicstyle=\ttfamily\small,
    inputencoding=utf8,
    extendedchars=\true,
    backgroundcolor=\color{black!10},
    breaklines=true,
% This works
    postbreak=\mbox{$\hookrightarrow$\space},
% This does not work
    postbreak=\mbox{\textcolor{red}{$\hookrightarrow$}\space},
}


\begin{document}

\begin{frame}[fragile]{Test}
\begin{lstlisting}
This is a long line. This is a long line. This is a long line. This is a long line. This is a long line.
This is another long line. This is another long line. This is another long line. This is another long line.
\end{lstlisting}
\end{frame}
\end{document}

Here is the output of the code, without the \textcolor obviously.

If I uncomment the postbreak line, I get this error :

! Missing number, treated as zero.
<to be read again> 
                   \kern 
l.3 This 
         is a long line. This is a long line. This is a long line. This is a...
A number should have been here; I inserted `0'.
(If you can't figure out why I needed to see a number,
look up `weird error' in the index to The TeXbook.)

Any ideas on why does the textcolor makes things crash ?

Answer 1

As was already suggested in other answers, you should place the arrow inside a box, which will help in the fragile environment:

\documentclass[xcolor={svgnames,usenames,dvipsnames,table}]{beamer}
\usepackage[utf8]{inputenc} 
\usepackage[T1]{fontenc}
\usepackage{amssymb}
\usepackage{listings}

\newsavebox{\mypostbreak}
\savebox{\mypostbreak}{\mbox{\textcolor{red}{$\hookrightarrow$}\space}}
\lstset{%
    xleftmargin=3.4pt,
    xrightmargin=3.4pt,
    %keepspaces=true,
    columns=fullflexible,   % Rasterize the columns
    frame=single,
    basicstyle=\ttfamily\small,
    inputencoding=utf8,
    extendedchars=\true,
    backgroundcolor=\color{black!10},
    breaklines=true,
% This works
    % postbreak=\mbox{$\hookrightarrow$\space},
% This now also works
    postbreak=\usebox{\mypostbreak},
}

\begin{document}

\begin{frame}[fragile]{Test}
\begin{lstlisting}
This is a long line. This is a long line. This is a long line. This is a long line. This is a long line.
This is another long line. This is another long line. This is another long line. This is another long line.
\end{lstlisting}
\end{frame}
\end{document}