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https://issues.apache.org/jira/browse/LUCENE-5441?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13895937#comment-13895937
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Shai Erera commented on LUCENE-5441:
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+1 to make the separation, I was thinking exactly that while working on
LUCENE-5440. I wish also that DocIdSet (or some other interface) allowed you to
do set operations, e.g. like Solr's DocSet. This then makes
optimization-checking {{if (bits instanceof FixedBitSet)}} moot, you just call
docs.intersect(otherDocIdSet) and let the implementation decide if it can
optimize or not. It should then be pretty easy to implement a DocSet/DocIdSet
backed by a FixedBitSet?
> Decouple DocIdSet from OpenBitSet and FixedBitSet
> -------------------------------------------------
>
> Key: LUCENE-5441
> URL: https://issues.apache.org/jira/browse/LUCENE-5441
> Project: Lucene - Core
> Issue Type: Task
> Components: core/other
> Affects Versions: 4.6.1
> Reporter: Uwe Schindler
> Fix For: 5.0
>
>
> Back from the times of Lucene 2.4 when DocIdSet was introduced, we somehow
> kept the stupid "filters can return a BitSet directly" in the code. So lots
> of Filters return just FixedBitSet, because this is the superclass (ideally
> interface) of FixedBitSet.
> We should decouple that and *not* implement that abstract interface directly
> by FixedBitSet. This leads to bugs e.g. in BlockJoin, because it used Filters
> in a wrong way, just because it was always returning Bitsets. But some
> filters actually don't do this.
> I propose to let FixedBitSet (only in trunk, because that a major backwards
> break) just have a method {{asDocIdSet()}}, that returns an anonymous
> instance of DocIdSet: bits() returns the FixedBitSet itsself, iterator()
> returns a new Iterator (like it always did) and the cost/cacheable methods
> return static values.
> Filters in trunk would need to be changed like that:
> {code:java}
> FixedBitSet bits = ....
> ...
> return bits;
> {code}
> gets:
> {code:java}
> FixedBitSet bits = ....
> ...
> return bits.asDocIdSet();
> {code}
> As this methods returns an anonymous DocIdSet, calling code can no longer
> rely or check if the implementation behind is a FixedBitSet.
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