code: public static <U, S extends 
        UpdatableSummary<U>> UpdatableSketch<U, S> heapifyUpdatableSketch(final Memory mem,
            final SummaryDeserializer<S> deserializer, final SummaryFactory<S> summaryFactory) {
      return new UpdatableSketch<U, S>(mem, deserializer, summaryFactory);
    }
docs: Instantiate UpdatableSketch from a given Memory
  @param <U> Type of update value
  @param <S> Type of Summary
  @param mem Memory object representing a Sketch
  @param deserializer instance of SummaryDeserializer
  @param summaryFactory instance of SummaryFactory
  @return Sketch created from its Memory representation