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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1614) Add next() and skipTo() variants to DocIdSetIterator that return the current doc, instead of boolean
Date Thu, 21 May 2009 11:41:45 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1614?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12711576#action_12711576
] 

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

bq. I think I'll emphasize that in the javadocs, documenting the limitation of MAX_VAL so
that people won't assume the wrong things.

+1

A docID is different from an "int", because docIDs must be 0 .. MAX_VAL-1.

{quote}
Why? just because OBSI declared a method which we wanted anyway? You know .. it's something
we don't give much thought to when we add methods to abstract classes, but what if someone
extended DISI and added his own advance(int) or nextDoc() which don't behave like we expect
them to. When he'll pass his DISI to the search flow somehow, not knowing these have become
the primary methods, something will break.

I'm not saying we should protect these cases too, because otherwise we won't be able to make
any changes. But just because OBSI had nextDoc() declared doesn't mean we should go and find
a different name. That's slightly unrelated to this issue, but our back-compat policy forces
us to replace good names with moderate ones, just because we cannot change methods.
{quote}

You're right, a random subclass of an abstract class could very well choose the name we are
wanting to add, and then their class fails to compile, or (if the sigs turn out to be identical)
runs bug possibly causes problems.

But in this case we know we have just such a class that has done so (OBSI).  And of course
it did so for exactly the reasons that we are now wanting to add nextDoc to DISI.  My guess
is eg Solr probably relies heavily on OBSI.nextDoc returning -1 when it's done and we're gonna
cause AIOOB exceptions if we up and change to returning MAX_VAL.

bq.  That's slightly unrelated to this issue, but our back-compat policy forces us to replace
good names with moderate ones, just because we cannot change methods.

As much as it bothers me having to accept inferior names (so they don't conflict with the
existing names), I think it's very much the lesser-of-evils here.

> 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
>
>
> 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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