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https://issues.apache.org/jira/browse/LUCENE-1614?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12715431#action_12715431
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Shai Erera commented on LUCENE-1614:
------------------------------------

This is all to support jar drop-in ability. So say you wrote your own DISI with 
doc(), next() and skipTo() and now pass it to 2.9. The code in 2.9 will call 
nextDoc(), but you have implemented docID(), just doc(). Therefore nextDoc() 
cannot call docID(), same as it calls next() which is also deprecated.

We cannot implement docID() by calling doc() either, since docID() defines new 
semantics, which existing doc() implementations may not adhere to.

Of course, if someone chooses to change his/her code, he/she should override 
all 3 and provide his/her own implementation, especially since all 3 of them 
will become abstract in 3.0.

I actually meant to say "Since all DISIs should have their *doc()* implemented 
..." - that's the jar drop-in ability side of the story. Not all DISIs will 
have their docID() implemented. In fact none of them will, unless someone 
upgrades his code.

Right?

> 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, 
> 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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