code: func (it *Materialize) Size() (int64, bool) {
  	if it.hasRun && !it.aborted {
  		if clog.V(2) {
  			clog.Infof("returning size %v", it.actualSize)
  		}
  		return it.actualSize, true
  	}
  	if clog.V(2) {
  		clog.Infof("bailing size %v", it.actualSize)
  	}
  	return it.subIt.Size()
  }
docs: // Size is the number of values stored, if we've got them all.
  // Otherwise, guess based on the size of the subiterator.