Question

Essentially I have the task of writing two methods: a zip method that turns a generic tuple containing two lists of generic objections into a list of tuples made up of elements of the aforementioned lists, and an unzip method that does the same thing in the other direction. I.e.:

({1, "banana", true}{asgard, 5.21e, "stupidhomework"})
=> unzip
{(1, asgard)("banana",5.21e)(true,"stupidhomework")}
=> zip
({1, "banana", true}{asgard, 5.21e, "stupidhomework"})

Further complicating this: the list is a simply linked immutable generic list with the structure

List<T>
public final T       head;
public final List<T> tail;

…And the tuples are equally generic; both elements of the tuple can be literally anything:

public class Tuple<A, B> {
public final A a;
public final B b;

So here’s my problem: I have no idea how to get at elements a second layer down. For example, normally, I’d just do this-

   public static<A, B extends List> List unzip(Tuple<A, B> ListenTuple){
        List TupelnListe = new List(new Tuple(ListenTuple.a.head, ListenTuple.b.head));

-To get at the elements I need, two layers down. Unfortuantely, because Tuple is generic, it doesn’t know that ListenTuple.a has to be a List, and therefore has a head. The analogous problem arises in zip with getting at a and b from the tuple. Oh, and I’m not allowed to typecast for some stupid arbitrary reason, although I’m not sure how that would help me.

…Basically, can anyone give me a pointer on how to get this started? They basically threw us into generics in class this week, and nobody gets it. Any assistance would be much appreciated.

Answer 1

Would this work?

public static<A, B> List zip(Tuple<List<A>, List<B>> ListenTuple){

So that A and B are the elements of the list and a, b are now lists.

I am more familiar with C++ so am not sure if the differences prevent this somehow.