Method insert

src/ifcparse/map_variant.h:163–173

    }

    std::pair<iterator, bool> insert(const value_type& val) {
        return std::visit([this, &val](auto m) -> std::pair<iterator, bool> {
            // @todo is monostate still necessary here?
            if constexpr (!std::is_same_v<std::decay_t<decltype(m)>, std::monostate>) {
                auto result = m->insert(val);
                return { iterator(result.first), result.second };
            } else {
                return { end(), false };
            }
        }, map_);
    }
};