Slave duplicate counter

Question

Is it possible to create a counter that is a "slave" to another (master) counter, but also an exact duplicate?

The \@addtoreset{<slave>}{<master>} resets <slave> whenever <master> is incremented (similar functionality is offered by chngcntr), but I don't know about anything incrementing one counter (<slave>) automatically whenever another counter (<master>) is incremented.

The idea is to have a macro (say) \dupcntr{<slave>}{<master>} as an analogue to \@addtoreset. The application for this might be where one is interested in renaming a counter used/provided by a package into something more meaningful for the user (say, <slave>), without having to reference <master>. Or, if the original counter contains @ that needs to be escaped every time it's used, it is sometimes more convenient to have a "more user friendly" counter.

I know one way around is to use a macro that returns the value of <master>, but is it possible to perform the same manipulation with a macro than one could with the counter? Manipulation here refers to the printing of the counter (via \the<slave>) and perhaps it's representation (like \arabic, \alph, ...).

Answer 1

If both should have always the same value, why not simply \let the slave to the master? This copies the internal reference to the \count register.

\newcommand*{\dupcntr}[2]{%
    \expandafter\let\csname c@#1\expandafter\endcsname\csname c@#2\endcsname
}

This is for LaTeX counters. For TeX count's simply remove the c@ (if given by cs name) or use \let#1#2 if given by control sequence.

Answer 2

Check out my "amsthm tweaks": posted here. I did just this, because the amsthm package is lazy about making subordinate theorem numbers, and this breaks the fncylab package's way of customizing \ref's output. The code is thus:

\makeatletter
\newcommand{\clonecounter}[2]{
  \@xp\xdef\csname c@#1\endcsname{\@xp\@nx\csname c@#2\endcsname}
  \@xp\xdef\csname the#1\endcsname{\@xp\@nx\csname the#2\endcsname}
  % This is for hyperref compatibility
  \@xp\xdef\csname theH#1\endcsname{\@xp\@nx\csname theH#2\endcsname}
  % Don't copy p@#2 or cl@#2!
  \global\@xp\let\csname p@#1\endcsname = \@empty
  \global\@xp\let\csname cl@#1\endcsname = \@empty
  % This is wrong, for some reason.  So it's commented out.
  %\@addtoreset{#1}{@ckpt}
 }
\makeatother

This makes a new counter #1 which, at its birth, is a complete slave to #2: same count register, same manner of printing. It sets up all the internal quantities that LaTeX considers to constitute a "counter", so you can \addtocounter and \refstepcounter and \@addtoreset correctly.

Answer 3

Heiko Oberdiek's aliascnt package provides this functionality. It provides \newaliascnt{<slave>}{<master>} and can be used in instances where theorems share base counters:

\documentclass{article}
\usepackage{aliascnt}% http://ctan.org/pkg/aliascnt
\newtheorem{foo}{Foo}% counter "foo"
\newaliascnt{bar}{foo}% alias counter "bar"
\setlength{\parindent}{0pt}% Just for this example
\begin{document}
\setcounter{foo}{10}%
\begin{foo}Something\end{foo}
\verb|foo:|\ \thefoo \par
\verb|bar:|\ \thebar
\end{document}

As expected, it integrates well with hyperref.

Answer 4

The package assoccnt and its successor xassoccnt provides exactly this feature, "a way of associating counters to an existing driver counter so that incrementing the driver counter will increase its associated counters as well."

Here is a small example:

\documentclass{article}

\usepackage{assoccnt}
\newcounter{mysection}
\DeclareAssociatedCounters{section}{mysection}

\begin{document}

\thesection\ \themysection

\section{A section} \thesection\ \themysection

\end{document}

Answer 5

ConTeXt presents a key-value interface to couple two counters. For example:

\definecounter
  [first]
  [numberconversion=Characters]

\definecounter
  [second]
  [number=first, numberconversion=numbers]

\starttext

\incrementcounter[first]
\incrementcounter[first]

\convertedcounter[first] % Prints "B"
\convertedcounter[second]% Prints "2"

\stoptext

If you want the second counter to inherit all the settings of the first counter, (conversion, color, style, etc), just use

\definecounter
   [second]
   [first]