class_docstr: Instead of marching the sub-matchers along in parallel, this matcher
  pre-reads the scores for a large block of documents at a time from each
  matcher, accumulating the scores in an array.
  
  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 id(self):
      return self._docnum
  
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 12 for calling the ArrayUnionMatcher obj's underlying member method code with example usage: obj.id() and returns: self