How can I define a new environment which limits the scope of \newtheorem commands?

Question

I am attempting to make an environment out of the command given in one of the answers to this question: Customizing theorem name.

\documentclass{article}
\usepackage{amsmath}
\usepackage{amsthm}

\newenvironment{namedtheorem}[1]{
\theoremstyle{definition}
   \newtheorem*{thmTemp}{#1}
\begin{thmTemp}}{\end{thmTemp}}

\begin{document}

\begin{namedtheorem}{foo}
    This is a named theorem bar.
\end{namedtheorem}

\begin{namedtheorem}{bar}
    This is a named theorem bar.
\end{namedtheorem}

\end{document}

Unfortunately, my invocation of \newtheorem*{thmTemp}{#1} seems to be scoping beyond the current environment, causing an error when the environment is used a second time.

How can I fix my environment to avoid this problem?

Answer 1

As far as I can see, Andrew Stacey's answer to your other question is providing you with an environment for these named theorems. The only difference from your request, is that the name is an optional argument. Using his code, we can define a new environment, where the name is required, by using the result of his definition and providing the argument:

\newenvironment{namedtheorem}[1]{\begin{internalnamedtheorem}[#1]}{\end{internalnamedtheorem}}

This way, we move the \newtheorem command out of the environment definition. This is close to a common (La)TeX coding idiom, when main commands are defined in terms of other secondary commands.

\documentclass{article}

\usepackage{amsthm}

\newtheorem*{theorem}{Theorem}

\newtheoremstyle{named}{}{}{\itshape}{}{\bfseries}{.}{.5em}{\thmnote{#3's }#1}
\theoremstyle{named}
\newtheorem*{internalnamedtheorem}{Theorem}

\newenvironment{namedtheorem}[1]{\begin{internalnamedtheorem}[#1]}{\end{internalnamedtheorem}}

\begin{document}

\noindent
Standard naming.

\begin{theorem}[Euclid]
  There are infinitely many primes.
\end{theorem}

\noindent
New naming.

\begin{namedtheorem}{Euclid}
  There are infinitely many primes.
\end{namedtheorem}

\end{document}