Iterator.unfoldRight() eagerly evaluates provided function

[etsinko]

I recently noticed that the returned iterator always evaluates supplied function. Even if the iterator.next() or iterator.hasNext() is never called.
Moreover, the iterator will eagerly preload next element on iterator.getNext() call.
Both of these issues could be avoided by wrapping nextVal in Lazy. So instead of this:

    static <T, U> Iterator<U> unfoldRight(T seed, Function<? super T, Option<Tuple2<? extends U, ? extends T>>> f) {
        Objects.requireNonNull(f, "the unfold iterating function is null");
        return new AbstractIterator<U>() {
            private Option<Tuple2<? extends U, ? extends T>> nextVal = f.apply(seed);

            @Override
            public boolean hasNext() {
                return nextVal.isDefined();
            }

            @Override
            public U getNext() {
                final U result = nextVal.get()._1;
                nextVal = f.apply(nextVal.get()._2);
                return result;
            }
        };
    }

the following can be used:

    static <T, U> Iterator<U> unfoldRight(T seed, Function<? super T, Option<Tuple2<? extends U, ? extends T>>> f) {
        Objects.requireNonNull(f, "the unfold iterating function is null");
        return new AbstractIterator<U>() {
            private Lazy<Option<Tuple2<? extends U, ? extends T>>> nextVal = Lazy.of(() -> f.apply(seed));

            @Override
            public boolean hasNext() {
                return nextVal.get().isDefined();
            }

            @Override
            public U getNext() {
                Tuple2<? extends U, ? extends T> tuple = nextVal.get().get();
                final U result = tuple._1;
                nextVal = Lazy.of(() -> f.apply(tuple._2));
                return result;
            }
        };
    }