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From "Franco Callari (JIRA)" <j...@apache.org>
Subject [jira] [Created] (LUCENE-4314) The specification of DocIdSetIterator is needlessly ambiguous.
Date Mon, 20 Aug 2012 02:28:37 GMT
Franco Callari created LUCENE-4314:
--------------------------------------

             Summary: The specification of DocIdSetIterator is needlessly ambiguous.
                 Key: LUCENE-4314
                 URL: https://issues.apache.org/jira/browse/LUCENE-4314
             Project: Lucene - Core
          Issue Type: Improvement
          Components: core/search
    Affects Versions: 4.0-BETA, 3.6.1
         Environment: All
            Reporter: Franco Callari


Quoth Lucene at org.apache.lucene.search.DocIdSetIterator.advance:

     "Advances to the first beyond (see NOTE below) the current whose document
      number is greater than or equal to <i>target</i>. [...]
      NOTE:</b> when <code> target &le; current</code> implementations
may opt
      not to advance beyond their current {@link #docID()}."

However, the same specification contradictorily states that advance must behave as if written:

     int advance(int target) {
       int doc;
       while ((doc = nextDoc()) < target) {}
       return doc;
     }

That is, with at least one call to nextDoc() always made, unconditionally.

This ambiguity can lead to unexpected behavior. In fact, arguably every user of this interface
that does not test after every call whether the iterator has exhausted AND has advanced is
incorrect.

For example, I myself had one experimental implementation (coded against a previous Lucene
release) that caused an infinite loop in PhraseScorer.java because, following the above specification,
it "opted" not to move the iterator when advance(target) was called with target < current.

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