Why does doublespacing using setspace have errors when used in a minimal documentclass?

Just curious why \doublespacing seems broken in a minimal document. It works ok when the documentclass is set to article.

\documentclass{minimal}
\usepackage{setspace}
\doublespacing

\begin{document}

doublespace

these

lines

\end{document}


First error is

! Undefined control sequence.

\setstretch ...ef \baselinestretch {#1}\@currsize

-

setspace depends on \@currsize being set by the documentclass to set the current font size. The minimal document class is very minimal and doesn't contain this macro. It doesn't even have things like \large.
Indeed, the minimal class is unfortunately pretty bad at supporting a lot of standard stuff, hence the recommendation that minimal examples should not use it! – Joseph Wright May 12 '11 at 16:29
\makeatletter