@Override
  public <IN, OUT> OUT apply(IN input, StartpointVisitor<IN, OUT> startpointVisitor) {
    return startpointVisitor.visit(input, this);
  }
Constructs a {@link Startpoint} that represents the latest offset in a stream partition.
samza-api/src/main/java/org/apache/samza/startpoint/StartpointUpcoming.java