Using \romannumeral in TeX to do multiple macro expansions

This blog post demonstrates a TeX macro hack: using \romannumeral to expand many macros in a single expansion. The example goal is to define a macro \stars which (when called properly) expands to the specified number of stars as a single expansion. Using a single expansion only makes the macro work in an \expandafter\def...{...} context. The similar macro given in The TeXbook doesn't work in this context because it needs multiple expansions.

\documentclass{article} 
%** Usage: \romannumeral\stars{NUMSTARS} 
%** This expands to a NUMSTARS stars (* tokens) in a single expansion step. 
\def\stars#1{% 
  \expandafter\mtostar\expandafter{\expandafter}\romannumeral\number#1 000z} 
\def\firstoftwo#1#2{#1}% 
\def\secondoftwo#1#2{#2}% 
\def\mtostar#1#2{% 
  \ifx#2z\expandafter\firstoftwo\else\expandafter\secondoftwo\fi 
  {0 #1}{\mtostar{#1*}}% 
} 
\begin{document} 
\expandafter\def\expandafter\mystars\expandafter{\romannumeral\stars{4}}% 
\texttt{(\meaning\mystars)} 
\end{document}