etoolbox conditionals with kvoptions string options

Question

I'm writing my first LaTeX class. After some research I've found that kvoptions seems to be the most recommended for key value class options, and etoolbox is recommended over ifthen for conditionals.

What's mystifying me is how one conditionally defines commands/passes options to packages based on the value of a kvoptions string option. Unfortunately I dont really have examples of what I've tried as I don't know where to start combining these two.

If there's another more ergonomic combination that can achieve this goal I'm open to it. I'm not particularly attached to either package. Any pointers would be hugely appreciated.

Answer 1

Provided that you need both, evaluation whether some special value is set, and at the same time store the value, you can use expkv-opt and the defining front end in expkv-def (disclaimer: I'm the author of those packages).

We set up the key to store every value inside \myopt, additionally we specify what to do for specific values (and to ignore unknown choices for the choice-code behaviour).

I use expkv-def for its ability to overload keys with several types using the also prefix.

\begin{filecontents*}[overwrite]{\jobname.cls}
\RequirePackage{expkv-def,expkv-opt}
\ProvidesClass{\@currname}[2025-08-31 v0.0 an adhoc class for an MWE]

\newcommand\mysimplebool[2]{#2} % this is basically 'false'

% forward all options to our base class
\LoadClassWithOptions{article}

\ekvdefinekeys{\@currname}
  {
    % general behaviour of storing inside a variable
             store  myopt = \myopt
    % handling of a select few special values
    ,also    choice myopt =
      {
         special-value = \let\mysimplebool\@firstoftwo
        ,other-value   = \let\mysimplebool\@secondoftwo
      }
    % ignore unknown choices
    ,unknown-choice myopt = {}
  }
\ekvoProcessGlobalOptions{\@currname}

% additional setup macro to set keys outside of the optional argument
\protected\ekvsetdef\myclssetup{\@currname}

\end{filecontents*}

\documentclass[12pt,myopt=special-value]{\jobname}

\begin{document}
\mysimplebool{true}{false}

We also stored the value: \myopt.
\end{document}

---

If you don't need to actually store the value but only want to accept specific ones, simply drop the store and the also prefix (and if you want errors to be thrown drop unknown-choice as well).

Or, if you don't need the overloading functionality, you might want to consider the kernel's key=value interface. Search for ltkeys or l3keys, there should be questions on the site about those.

Answer 2

If you prefer a no-package solution you can use the built in key=value and options handler. Output looks as in my other answer.

\begin{filecontents*}[overwrite]{\jobname.cls}
\ProvidesExplClass{\@currname}
  {2025-08-31} {0.0} {an adhoc class for an MWE}

\DeclareKeys
  {
     myopt .tl_set:N = \myopt
  }

% forward all unknown options to our base class
\DeclareUnknownKeyHandler{\PassOptionsToClass{\CurrentOption}{article}}

\ProcessKeyOptions

\LoadClass{article}

\NewExpandableDocumentCommand \mysimplebool { m m }
  { \str_if_eq:VnTF \myopt { special-value } {#1} {#2} }
\end{filecontents*}

\documentclass[12pt,myopt=special-value]{\jobname}

\begin{document}
\mysimplebool{true}{false}

We also stored the value: \myopt.
\end{document}