code: static UnionImpl heapifyInstance(final Memory srcMem, final long seed) {
      Family.UNION.checkFamilyID(extractFamilyID(srcMem));
      final UpdateSketch gadget = HeapQuickSelectSketch.heapifyInstance(srcMem, seed);
      final UnionImpl unionImpl = new UnionImpl(gadget, seed);
      unionImpl.unionThetaLong_ = extractUnionThetaLong(srcMem);
      unionImpl.unionEmpty_ = PreambleUtil.isEmpty(srcMem);
      return unionImpl;
    }
docs: Heapify a Union from a Memory Union object containing data.
  Called by SetOperation.
  @param srcMem The source Memory Union object.
  <a href="{@docRoot}/resources/dictionary.html#mem">See Memory</a>
  @param seed <a href="{@docRoot}/resources/dictionary.html#seed">See seed</a>
  @return this class