/*      attr_set(option, arg)        */
static VALUE stmt_attr_set(VALUE obj, VALUE opt, VALUE val)
{
    struct mysql_stmt* s = DATA_PTR(obj);
    check_stmt_closed(obj);
    if (NUM2INT(opt) == STMT_ATTR_UPDATE_MAX_LENGTH) {
        my_bool arg;
        arg = (val == Qnil || val == Qfalse) ? 0 : 1;
        mysql_stmt_attr_set(s->stmt, STMT_ATTR_UPDATE_MAX_LENGTH, &arg);
        return obj;
    }
    rb_raise(eMysql, "unknown option: %d", NUM2INT(opt));
}