How to reference the most recently used multiply-defined label

Question

I want to be able to do something like the following:

\incmycounter{abc}  %% counter value initialized to 0; associated with label 'abc'
\incmycounter{def}  %% counter value initialized to 0; associated with label 'def'
... various text (including some calls to \incmycounter) ...
\incmycounter{abc}  %% counter value == 2; associated with label 'abc'
\incmycounter{def}  %% counter value == 100;  associated with label 'def'
... some text (possibly defining new sections, labels, etc.) ...
\myref{abc} %% generate '2'
... more text ...
\myref{abc} %% generate '2'
\incmycounter{abc}  %% counter value == 3; associated with label 'abc'
... more text ...
\myref{abc} %% generate '3'
\myref{def} %% generate '100'

The \incmycounter command should either initialize a new counter (associated with the provided label name), or increment a currently defined one. A given \myref command should always refer to / generate the value that the associated counter had after the preceding \incmycounter command was executed. Is this possible, and if so, how?

Answer 1

You could just define a macro to store and change the values as necessary, without using a \label-\ref:

\documentclass{article}
\makeatletter
\newcommand{\mycounter}[2]{\global\@namedef{@cnt-#1}{#2}}
\newcommand{\myref}[1]{\@nameuse{@cnt-#1}}
\makeatother
\begin{document}
\mycounter{abc}{2}    %% new counter value == 2
\mycounter{def}{100}  %% new counter value == 100
\par \ldots some text (possibly defining new sections, labels, etc.) \ldots \par
\myref{abc} %% generate '2'
\par \ldots more text \ldots \par
\myref{abc} %% generate '2'
\mycounter{abc}{3}  %% new counter value == 3
\par \ldots more text \ldots \par
\myref{abc} %% generate '3'
\myref{def} %% generate '100'
\end{document}

\@namedef{<name>}{<stuff>} stores <stuff> in \<name>, while \@nameuse retrieves it. I've preceded the names with @cnt-, since \def (as in your example) is "already taken", while \@cnt-def is not. \global makes the change global, otherwise it could be trapped within an environment based on its scope. The use of \@namedef-\@nameuse (from the LaTeX kernel) also allows you (as in my example) to define names using characters that are usually not allowed.

The above example does not use counters, but it could be modified to allow for this. It didn't seem necessary from the code snippet.

---

Here is a modified version that uses counters, creating them if they don't already exist counter:

\documentclass{article}
\makeatletter
\newcommand{\incmycounter}[1]{%
  \@ifundefined{c@#1}
    {\newcounter{#1}}
    {\stepcounter{#1}}}
\newcommand{\myref}[1]{\@nameuse{the#1}}
\makeatother
\begin{document}
\incmycounter{abc}  %% counter value initialized to 0; associated with label 'abc'
\incmycounter{def}  %% counter value initialized to 0; associated with label 'def'
\par \ldots various text (including some calls to macros\incmycounter{abc}\incmycounter{def}) \ldots \par
\myref{abc} %% generate '1'
\par \ldots more text \ldots \par
\incmycounter{def}\myref{def} %% generate '2'
\incmycounter{abc}  %% counter value == 2
\par \ldots more text \ldots \par
\incmycounter{abc}\myref{abc} %% generate '3'
\myref{def} %% generate '100'
\end{document}

The first step in \incmycounter{<name>} is to check whether the counter <name> already exists. This is done using \@ifundefined{c@#1}, since all counters defined by \newcounter references a macro prepended with c@. So, the counter <name> is actually stored in \c@<name>. If it doesn't exist, then issue \newcounter{<name>}, otherwise \stepcounter{<name>}.

Another version using counters that could be used to set/step/arbitrarily increment the counters you use:

\documentclass{article}
\usepackage{xparse}% http://ctan.org/pkg/xparse
\makeatletter
\NewDocumentCommand{\mycounter}{s O{1} m}{%
  \@ifundefined{c@#3}
    {\newcounter{#3}}
    {\IfBooleanTF{#1}
       {\setcounter{#3}{#2}}
       {\addtocounter{#3}{#2}}}}
\newcommand{\myref}[1]{\@nameuse{the#1}}
\makeatother
\begin{document}
\mycounter{abc}  %% counter value initialized to 0; associated with label 'abc'
\mycounter{def}  %% counter value initialized to 0; associated with label 'def'
\par \ldots various text (including some calls to macros\mycounter{abc}\mycounter{def}) \ldots \par
\myref{abc} %% generate '1'
\par \ldots more text \ldots \par
\mycounter{def}\myref{def} %% generate '2'
\mycounter{abc}  %% counter value == 2
\par \ldots more text \ldots \par
\mycounter{abc}\myref{abc} %% generate '3'
\mycounter*[100]{def}%% counter value == 100
\myref{def} %% generate '100'
\end{document}

This uses xparse to provide the command interface. Now \mycounter[<value>]{<cntr>} increments <cntr> by <value> or sets <cntr> to <value> in the optional starred version (\mycounter*[<value>]{<cntr>}).

Answer 2

As I understand what you're saying, you could write:

\newcounter{myabc}
\newcounter{mydef}
\setcounter{myabc}{2}
\setcounter{mydef}{100}

.... some text ....

\themyabc %% geenerate '2'
\stepcounter{myabc}

.... more text ....

\themyabc %% generates '3'
\themydef %% generate '100'

If you could provide a bit more context, I could probably give you an answer that better meets your needs.

Here's how to get \myref to work with the approach I've outlined above:

\documentclass{article}
\newcounter{abc}
\makeatletter
\newcommand{\myref}[1]{\@nameuse{the#1}}
\makeatother
\begin{document}
\setcounter{abc}{3}
\theabc\ compared to \myref{abc}
\end{document}

which is really werner and not me.

Here's why I think @werner's solution is better:

1. It's very user friendly: you don't have to remember how to set things up. With my approach, you have to remember that there's a counter to be define, that the counter needs to be stepped, etc. etc.

2. In six months or a year from now you might think, "What was that really cool trick I did?" As I've written it, there's very little to remind you of all the steps you need to take to recreate the effect. Werner's solution is compact and---provided you're comfortable reading TeX and LaTeX code---is relatively self-explanatory (with or without comments).

3. Werner's approach is extremely malleable. Maybe in a week from now or a month later you'll realize that you want something more dynamic or you want these counters tied in with some other structure in your document such as chapters, theorem, etc. (I know your original posting seems to indicate that this is not your desire, but we often change our minds.) With this regard, my approach is extremely clunky and rife for mistakes.