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https://issues.apache.org/jira/browse/LUCENE-4314?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13439463#comment-13439463
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Franco Callari commented on LUCENE-4314:
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Michael, you are welcome. Thanks for the quick review.
> 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: 3.6.1, 4.0-BETA
> Environment: All
> Reporter: Franco Callari
> Assignee: Michael McCandless
> Labels: index,, iterators
> Fix For: 5.0, 4.0
>
> Attachments: DocIdSetIterator.patch
>
>
> 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 ≤ 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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