mjhjmtu

With the array package we can define a new column specifier that can be used in a tabular environment (e.g. newcolumntypeA[>centering arraybackslashm2cm).

It is even allowed to define a new column type with an argument like newcolumntypeB[1]>centering arraybackslashm#1.

Now I need to let the new colomn type argument have a default value like newcolumntypeC[1][2cm]>centering arraybackslashm#1 but this results in a compilation error.

So I am asking if it is possible to provide a default argument to the newcolumntype command?

MWE

documentclassarticle
usepackagearray
newcolumntypeA[1]>centering arraybackslashm#1

%newcolumntypeB[1]{3cm]>centering arraybackslashm#1

begindocument
 begintabularhline
 column width = 2 cm & column width= 4cm \hline
 hello world hello world hello world & hello world hello world hello world\hline
 endtabular
enddocument

You can not do that without somewhat extensive changes to the array package, adding the declaration possibility would be simple but the mechanism used to replace defined columntypes does not have anything that would help detect optional parameters, so you would have to change that mechanism, and doing that without breaking packages that depend on it (colortbl, tabularx, tabulary, ....) might be tricky.

If you accept an empty argument rather than an optional one it is easy, so the benefits of such a change compared to the risk of breaking existing code are rather discouraging adding such a feature.

newcolumntypeA[1]>centering arraybackslashmif!#1!3cmelse#1fi

would allow A to use a default width of 3cm