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Date: Fri, 29 May 2009 01:44:45 -0700 (PDT)
From: "Michael McCandless (JIRA)" <jira@apache.org>
To: java-dev@lucene.apache.org
Subject: [jira] Commented: (LUCENE-1614) Add next() and skipTo() variants to
 DocIdSetIterator that return the current doc, instead of boolean
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    [ https://issues.apache.org/jira/browse/LUCENE-1614?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12714366#action_12714366 ] 

Michael McCandless commented on LUCENE-1614:
--------------------------------------------

bq. Consider the code in BS2 which checks if it should call nextDoc() before the while loop (the score(Collector, int) method). If a DISI decided to return '2' simply because the first doc available is '3', then we may incorrectly collect '2'.

Actually, I'm not liking that particular added code anyway ;)

Ie the contract of that method (I believe) is that nextDoc must already have been called.  I don't like adding ambiguity into the API, and so instead of the check I'd rather switch it to an "assert docID != -1", ie, assert that nextDoc was in fact called.  And then if that assert trips up, we need to go understand the root cause for that.

bq. So I say we relax the policy in this way: "an implementation can return -1 if it knows the iterator is not exhausted, or NO_MORE_DOCS otherwise".

OK, let's do that.  Though: it need not return NO_MORE_DOCS up front, right?  Ie, if it is able to determine up front it has no docs to iterate, great, else, it can return -1 until nextDoc() is called at which point it returns NO_MORE_DOCS?

> Add next() and skipTo() variants to DocIdSetIterator that return the current doc, instead of boolean
> ----------------------------------------------------------------------------------------------------
>
>                 Key: LUCENE-1614
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1614
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Search
>            Reporter: Shai Erera
>             Fix For: 2.9
>
>         Attachments: LUCENE-1614.patch, LUCENE-1614.patch, LUCENE-1614.patch, LUCENE-1614.patch, LUCENE-1614.patch, LUCENE-1614.patch, LUCENE-1614.patch
>
>
> See http://www.nabble.com/Another-possible-optimization---now-in-DocIdSetIterator-p23223319.html for the full discussion. The basic idea is to add variants to those two methods that return the current doc they are at, to save successive calls to doc(). If there are no more docs, return -1. A summary of what was discussed so far:
> # Deprecate those two methods.
> # Add nextDoc() and skipToDoc(int) that return doc, with default impl in DISI (calls next() and skipTo() respectively, and will be changed to abstract in 3.0).
> #* I actually would like to propose an alternative to the names: advance() and advance(int) - the first advances by one, the second advances to target.
> # Wherever these are used, do something like '(doc = advance()) >= 0' instead of comparing to -1 for improved performance.
> I will post a patch shortly

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