@Override
    public Map<Uuid, Set<Integer>> partitions() {
        return memberAssignment.partitions();
    }
Constructs a new {@code MemberSubscriptionAndAssignmentImpl}.

@param rackId                The rack Id.
@param subscribedTopicIds    The set of subscribed topic Ids.
@param memberAssignment      The current member assignment.
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/modern/MemberSubscriptionAndAssignmentImpl.java