Add index with Java8 Stream.map (tuple version)

Preface

i02302's Add index with Stream.map after Java8 described how to add index to each element of Stream.

When I first saw it, I was using an array for the index counter, and I thought it would be better to use an atomic Integer in consideration of parallel Streams ... but when I saw it earlier, it changed so (laughs).

After that, if you use BiFuntion, the index part of int will be Integer, so I think it is better to prepare your own functional interface.

public interface BiIntFunction<T, R> {
	public R apply(T t, int n);
}

public class WithIndex {
	public static <T, R> Function<T, R> apply(int start, BiIntFunction<T, R> function) {
		AtomicInteger counter = new AtomicInteger(start);
		return object -> function.apply(object, counter.getAndAdd(1));
	}
}

stream.map(WithIndex.apply(1, (obj, i) -> obj + i))

How to prepare tuples

Scala's zipWithIndex returns an element-index pair (tuple), so it's the same. I think there is also a way to do it.

public class ObjectIndexPair<T> {
	private final T object;
	private final int index;

	private ObjectIndexPair(T object, int index) {
		this.object = object;
		this.index = index;
	}

	public T getObject() {
		return object;
	}

	public int getIndex() {
		return index;
	}

	public static <T> Function<T, ObjectIndexPair<T>> start(int start) {
		AtomicInteger counter = new AtomicInteger(start);
		return object -> new ObjectIndexPair<>(object, counter.getAndAdd(1));
	}
}

stream.map(ObjectIndexPair.start(1)).map(pair -> pair.getObject() + pair.getIndex())