@Override
        public boolean hasNext() {
            for (int iterateDimension : iterateDimensions) {
                if (indexes[iterateDimension] + 1 < dimensionSizes().size(iterateDimension))
                    return true; // some dimension is not at the end
            }
            return false;
        }
Advances this to the next cell in the standard indexed tensor cell order.
The first call to this will put it at the first position.

@throws RuntimeException if this is called when hasNext returns false
vespajlib/src/main/java/com/yahoo/tensor/IndexedTensor.java