General ⇒ Change variable of a package

[bstex]

Hi.
I'm using mhchem and I'd like to change the default length of the variable \__mhchem_arrow_options_minLength:n
(It's on the line 1015 of the mhchem.sty file.)

What should I type in my preamble after \usepackage[version=4]{mhchem} to change this length?
The developer of this package told me that there is no public API, so I could experiment with this variable.
Thank you very much.

[Johannes_B]

Hi,
Minimal working example please.

[bstex]

Sorry, here it is:

Code: Select all

\documentclass[a4paper,11pt]{book}
\usepackage{tikz}
\usetikzlibrary{positioning,arrows.meta}
\usepackage[version=4]{mhchem}

\begin{document}

\mhchemoptions{arrows=pgf{Straight Barb[round, angle=60:1.5pt 3]}{0.1ex}}
\ce{A -> B} \\
\ce{C <=> D} \\
\ce{E <=>[\text{testing}] F} \\

\end{document}

[Johannes_B]

Code: Select all

\documentclass[a4paper,11pt]{book}
    \usepackage{tikz}
    \usetikzlibrary{positioning,arrows.meta}
    \usepackage[version=4]{mhchem}
     
    \begin{document}
     
\ExplSyntaxOn
\cs_set:Npn \__mhchem_arrow_options_minLength:n  { {9em} }
\ExplSyntaxOff
    \mhchemoptions{arrows=pgf{Straight Barb[round, angle=90:1.5pt 3]}{0.1ex}}
    \ce{A -> B} \\
    \ce{C <=> D} \\
    \ce{E <=>[\text{testing}] F} \\
     
    \end{document}

[bstex]

Yes, that's it!
Thank you so much.

[cgnieder]

Oh wow! According to expl3 conventions \__mhchem_arrow_options_minLength:n is an internal function with one brace argument. According to \show and the MWE it is used as a length or skip variable. It really should be named something like

\l__mhchem_arrow_options_minLength_dim

and be set internally with \dim_set:Nn \l__mhchem_arrow_options_minLength_dim {2em} or similarly. But looking at the code this is just the tip of the iceberg of wrongly named and used expl3 code…

at the very least mhchem should provide an interface for setting the “variable” \__mhchem_arrow_options_minLength:n.