Member kblib::chooseCategorical (Array &&cats, RandomGenerator &r) -> decltype(cats.size()): std::discrete_distribution provides the same functionality, with a worse name. Because it exists, there is no reason to use this function.
Member kblib::coerce (const std::variant< Ts... > &v) -> To: Use lexical_coerce instead, as it more clearly expresses intent.
Member kblib::eat_space (std::istream &is): Use std::ws instead.
Member kblib::make_transform_iterator (base_iterator it, operation op) noexcept(noexcept(transform_iterator< base_iterator, operation >{ it, std::move(op)})) -> transform_iterator< base_iterator, operation >: Use transformer instead