Function tuple_or_struct_size

include/boost/parser/parser.hpp:2954–2961

        template<typename T>
        constexpr auto tuple_or_struct_size(T && x)
        {
            if constexpr (is_tuple<remove_cv_ref_t<T>>{}) {
                return hl::size(x);
            } else {
                return llong<struct_arity_v<remove_cv_ref_t<T>>>{};
            }
        }

        template<typename T>
        struct attr_reset