Reported by Remi:

Now, i've tried to play with the .box/.val trying to implement the clojure Cursor protocol,
which iterate like it's an abstract linked list, so at each step either you return a new Cursor (a value type) or null at the end (which seems to be a good test for a nullable value type).

The following code compiles !
I had to had the fix method because the compier refuse to find any methods on Cursor.box


static value class Tuple {
     private final int index;
     private final int element;
               private Tuple(int index, int element) {
       this.index = index;
       this.element = element;
     }
   }
      static value class Cursor {
     private final int[] array;
     private final int index;
          private Cursor(int[] array, int index) {
       this.array = array;
       this.index = index;
     }
          Tuple current() {
       return new Tuple(index, array[index]);
     }
          Cursor.box next() {
       if (index + 1 == array.length) {
         return null;
       }
       return new Cursor(array, index + 1);
     }
   }
      private static Cursor.box indexedElements(int[] array) {
     if (array.length == 0) {
       return null;
     }
     return new Cursor(array, 0);
   }
      private static Cursor fix(Cursor.box cursor) {
     return cursor;
   }
      @Benchmark
   public int sum() {
     int sum = 0;
     for(Cursor.box cursor = indexedElements(ARRAY); cursor != null; cursor = fix(cursor).next()) {
       Tuple tuple = fix(cursor).current();
       sum += tuple.index + tuple.element;
     }
     return sum;
   }