[jira] [Created] (LUCENE-5441) Decouple DocIdSet from OpenBitSet and FixedBitSet

["Uwe Schindler (JIRA)" <ji...@apache.org>]

Uwe Schindler created LUCENE-5441:
-------------------------------------

             Summary: 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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