Change typeface size after \documentclass?

Question

I use the same tex file to create several different layouts with basically the same content. I have several switches and \ifthenelse constructs to control the layouts. Normally, I just have to set one or two boolean variables to activate a specific layout.

Some layouts require typeface size 10pt, some 11pt. Is it possible to change the size after \documentclass{article}? E.g., in a constuct such as:

\ifthenelse{\boolean{layoutA}}
  {\setlength{\typefacesize}{10pt}}
  {\setlength{\typefacesize}{11pt}}

Obviously, there is no \typefacesize. I would like to avoid having to change the typeface size in \documentclass all the time.

Answer 1

It's possible, but I don't know exactly what the ramifications would be. Use at your own risk:

\documentclass[10pt]{article}

\makeatletter
\newcommand\resetfontsize[1]{%
  \let\small\@undefined
  \let\footnotesize\@undefined
  \let\scriptsize\@undefined
  \let\tiny\@undefined
  \let\large\@undefined
  \let\Large\@undefined
  \let\LARGE\@undefined
  \let\huge\@undefined
  \let\Huge\@undefined
  \makeatletter
  \input{size#1.clo}
  \makeatother
}
\makeatother

\usepackage{lipsum}
\begin{document}
\lipsum[1]
\section{abc}
\lipsum[2]

\resetfontsize{12}
\lipsum[1]
\section{abc}
\lipsum[2]

\end{document}

Answer 2

The KOMA-Script classes allow to change font sizes mid-document. The command syntax is \changefontsizes[(new "normalsize" baselineskip)]{(new "normalsize" fontsize)}. The default value for the new baselineskip is 1.2 * fontsize.

\documentclass[10pt]{scrartcl}

\usepackage{blindtext}

\begin{document}

\section{foo}

\blindtext

\changefontsizes{12pt}

\section{bar}

\blindtext

\changefontsizes[18pt]{12pt}

\section{gnu}

\blindtext

\end{document}