Method operator->

src/ifcparse/map_variant.h:79–85

        }

        value_type* operator->() const {
            // @todo we need to make a copy here (stored in unique_ptr) because the
            // value_type appears to be pair<const K, V> instead of <K, V> or something
            // related...
            cached_value_ptr_ = std::make_unique<value_type>(**this);
            return cached_value_ptr_.get();
        }

        iterator& operator++() {
            std::visit([](auto& it) { ++it; }, it_var);