Collect contents of lists at beginning of document

Question

I would like to create a custom list environment that collects the contents of these lists and places it at the beginning of the document.

\begin{objectives}
\item See no evil.
\end{objectives}

lots of stuff 1

\begin{objectives}
\item Hear no evil.
\end{objectives}

lots of stuff 2

\begin{objectives}
\item Speak no evil.
\end{objectives}

lots of stuff 3

I would like the objectives environment to be defined so that the commands above have the same effect as

\begin{enumerate}
\item See no evil.
\item Hear no evil.
\item Speak no evil.
\end{enumerate}

lots of stuff 1

lots of stuff 2

lots of stuff 3

(The reason I can't just move the objectives to the start of the document manually is that my content is spread across multiple files that will be combined a la carte.) I know I can use the collect package to obtain the list at the end of the document by defining

\usepackage{collect}
\definecollection{ob}
\newenvironment{objective}{%
\collect{ob}{}{}}{\endcollect}

..earlier content..

\begin{enumerate}
\includecollection{ob}
\end{enumerate}

It seems that a solution would need to depend on \immediate\write\tempfile{} to create a temporary file to store the contents. However, each of my attempts to create a temporary file will only succeed if I place the list at the end.

I know it is possible to collect content to be placed at the beginning of a document because a table of contents or a list of figures does just that. I haven't been able to make heads or tails of the code in the todonotes package or tocloft package.

Could you please point me in the right direction?

Answer 1

You can use the built in mechanism for the table of contents:

\documentclass{article}
\usepackage{environ}

\usepackage{lipsum} % just for the example

\makeatletter
\newcommand{\printobjectives}{%
  \section*{Objectives}
  \begin{enumerate}
  \def\@noitemerr{\@latex@warning{Empty objective list}}%
  \@starttoc{obj}
  \end{enumerate}
}
\newcommand{\l@obj}[2]{#1}
\makeatother

\NewEnviron{objectives}
 {%
  \addcontentsline{obj}{obj}{%
    \noexpand\unexpanded{\unexpanded\expandafter{\BODY}}%
  }%
 }

\begin{document}

\printobjectives

\section{Main}

\begin{objectives}
\item See no evil.
\end{objectives}

\lipsum[2]

\begin{objectives}
\item Hear no evil.
\end{objectives}

\lipsum[3]

\begin{objectives}
\item Speak no evil.
\end{objectives}

\lipsum[4]

\end{document}

If you load hyperref, but don't require hyperlinks for the objective list, do

\let\originalcontentsline\contentsline
\usepackage{hyperref}

(the first line is to save the original meaning of \contentsline) and change the code between \makeatletter and \makeatother into

\makeatletter
\newcommand{\printobjectives}{%
  \section*{Objectives}                     
  \begin{enumerate}
  \let\contentsline\originalcontentsline
  \def\@noitemerr{\@latex@warning{Empty objective list}}%
  \@starttoc{obj}
  \end{enumerate}
}
\newcommand{\l@obj}[3]{#1}
\makeatother