class_docstr: Instead of marching the sub-matchers along in parallel, this
  matcher pre-reads the scores for EVERY MATCHING DOCUMENT, trading memory
  for speed.
  
  This is faster than the implementation using a binary tree of
  :class:`~whoosh.matching.binary.UnionMatcher` objects (possibly just
  because of less overhead), but it doesn't allow getting information about
  the "current" document other than the score, because there isn't really a
  current document, just an array of scores.
code: def next(self):
      a = self._a
      offset = self._offset
      place = self._docnum - offset
  
      place += 1
      while place < len(a) and a[place] == 0:
          place += 1
      self._docnum = place + offset
  
imports: from __future__ import division
  from array import array
  from whoosh.compat import xrange
  from whoosh.matching import mcore
label_desc: Use image node_id 5 for calling the PreloadedUnionMatcher obj's underlying member method code with example usage: obj.next() without return types