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Posted to dev@lucene.apache.org by "Uwe Schindler (JIRA)" <ji...@apache.org> on 2012/06/18 14:13:43 UTC
[jira] [Commented] (LUCENE-3866) Make
CompositeReader.getSequentialSubReaders() and the corresponding
IndexReaderContext methods return unmodifiable List
[ https://issues.apache.org/jira/browse/LUCENE-3866?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13395847#comment-13395847 ]
Uwe Schindler commented on LUCENE-3866:
---------------------------------------
I will later also upgrade MIGRATE.txt markdown.
> Make CompositeReader.getSequentialSubReaders() and the corresponding IndexReaderContext methods return unmodifiable List<R extends IndexReader>
> -----------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: LUCENE-3866
> URL: https://issues.apache.org/jira/browse/LUCENE-3866
> Project: Lucene - Java
> Issue Type: Improvement
> Reporter: Uwe Schindler
> Assignee: Uwe Schindler
> Fix For: 4.0
>
> Attachments: LUCENE-3866-step1.patch, LUCENE-3866-step2.patch, LUCENE-3866-step2.patch
>
>
> Since Lucene 2.9 we have the method getSequentialSubReader() returning IndexReader[]. Based on hardly-to-debug errors in user's code, Robert and me realized that returning an array from a public API is an anti-pattern. If the array is intended to be modifiable (like byte[] in terms,...), it is fine to use arrays in public APIs, but not, if the array must be protected from modification. As IndexReaders are 100% unmodifiable in trunk code (no deletions,...), the only possibility to corrumpt the reader is by modifying the array returned by getSequentialSubReaders(). We should prevent this.
> The same theoretically applies to FieldCache, too - but the party that is afraid of performance problems is too big to fight against that :(
> For getSequentialSubReaders there is no performance problem at all. The binary search of reader-ids inside BaseCompositeReader can still be done with the internal protected array, but public APIs should expose only a unmodifiable List. The same applies to leaves() and children() in IndexReaderContext. This change to list would also allow to make CompositeReader and CompositeReaderContext Iterable<R extends IndexReader>, so some loops would look nice.
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