Passing command as argument to `\DefineArrayVar` from `forarray`

Question

I need to pass 1,2,3,...,\Num to the variable list argument of the \DefineArrayVar command from the forarray package. If I pass it manually, everything works fine, but, when I pass a command instead, \DefineArrayVar gets confused and fails.

Here is my MWE:

\documentclass{article}
\usepackage{forloop}
\usepackage{forarray}
\newcommand{\Num}{4}
\newcounter{ct}
\setcounter{ct}{1}
\newcommand{\test}{%
    \forloop{ct}{1}{\value{ct}<\Num}{\thect,}\thect%
}
\DefineArrayVar{ArrayName}{@}
{,}{1,2,3,4} % <---- This works 
% {,}{\test} % <---- This doesn't work
% {,}{\forloop{ct}{1}{\value{ct} < \Num}{\thect,}\thect} % <---- This doesn't work either
{,}{4cm,0.8cm,0.6cm,1.6cm}
% This doesn't work
% \expandafter\DefineArrayVar\expandafter{ArrayName}{@}{,}{\test}{,}{4cm,0.8cm,0.6cm,1.6cm}
\DefineArrayDefault{,}{@}{2}{2}{ArrayName}
\begin{document}
\test % To see what 'forloop' is generating
\ArrayName % Proof that it's working (must print "0.8cm")
\end{document}

Based on this answer and this answer (which are very much related to my problem), I also tried to use (separately) \expandafter or \edef like so:

    \expandafter\DefineArrayVar\expandafter{ArrayName}{@}{,}{\test}{,}{4cm,0.8cm,0.6cm,1.6cm}

    \edef\test{\unexpanded\expandafter{\forloop{ct}{1}{\value{ct}<\Num}{\thect,}\thect}}

but it didn't work.

Well, since I do not understand big picture of what I am doing, I can't go further. How do I make it work?

Answer 1

Would you consider a different package to store and recall arrays?

listofitems supports array constructs and is nice because its array storage technique is fully expandable (that is to say, once read, the recall of array elements is fully expandable).

It also supports multi-dimensional arrays.

\documentclass{article}
\usepackage{listofitems}
\begin{document}
\readlist*\ArrayName{4cm,0.8cm,0.6cm,1.6cm}
ArrayName[2] is \ArrayName[2]
The array has \listlen\ArrayName[] elements.
The whole array is \foreachitem\z\in\ArrayName[]{\ifnum\zcnt=1\else,\fi\z}
\end{document}

Answer 2

The forloop and forarray packages are really outdated. With expl3 you get much more with enhanced flexibility.

Your needs can be fulfilled with “one-liners”.

\documentclass{article}
\ExplSyntaxOn
\NewDocumentCommand{\definelist}{mm}
 {% #1 = list name, #2 = items
  \clist_clear_new:c { l_leone_list_#1_clist }
  \clist_set:cn  { l_leone_list_#1_clist } { #2 }
 }
\NewExpandableDocumentCommand{\getlistitem}{mm}
 {% #1 = list name, #2 = number of item to retrieve
  \clist_item:cn  { l_leone_list_#1_clist } { #2 }
 }
\NewExpandableDocumentCommand{\getlistlen}{m}
 {% #1 = list name
  \clist_count:c  { l_leone_list_#1_clist }
 }
\ExplSyntaxOff
\definelist{ArrayName}{4cm,0.8cm,0.6cm,1.6cm}
\begin{document}
\getlistitem{ArrayName}{4}
X\makebox[\getlistitem{ArrayName}{4}][s]{a\hfil a}X
X\hspace*{1.6cm}X
\end{document}

The last example shows that you can use \getlistitem in any situation where a length is needed, since the list contains lengths.