code: static UnionImpl fastWrap(final WritableMemory srcMem, final long seed) {
      Family.UNION.checkFamilyID(extractFamilyID(srcMem));
      final UpdateSketch gadget = DirectQuickSelectSketch.fastWritableWrap(srcMem, seed);
      final UnionImpl unionImpl = new UnionImpl(gadget, seed);
      unionImpl.unionThetaLong_ = extractUnionThetaLong(srcMem);
      unionImpl.unionEmpty_ = PreambleUtil.isEmpty(srcMem);
      return unionImpl;
    }
docs: Fast-wrap a Union object around a Union Memory object containing data.
  This does NO validity checking of the given Memory.
  @param srcMem The source Memory 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