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https://issues.apache.org/jira/browse/LUCENE-6246?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14324601#comment-14324601
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Adrien Grand commented on LUCENE-6246:
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+1!
> Fix DocsEnum -> PostingsEnum transition
> ---------------------------------------
>
> Key: LUCENE-6246
> URL: https://issues.apache.org/jira/browse/LUCENE-6246
> Project: Lucene - Core
> Issue Type: Bug
> Reporter: Robert Muir
> Attachments: LUCENE-6246-trunk.patch, LUCENE-6246_backwards.patch
>
>
> The current back compat introduced in LUCENE-4524, does not really help the
> users calling e.g. LeafReader.termDocsEnum() or
> LeafReader.termPositionsEnum(), because the former's return value changes to
> PostingsEnum, its superclass, and the latter got removed.
> It also does not help users using TermsEnum.docs() or
> TermsEnum.docsAndPositions() which got removed and just replaced with
> postings().
> DocsEnum is different, but not deprecated, instead only used by some codecs
> as a convenience class. DocsAndPositionsEnum is removed.
> I think we can do this a little better. First, we need to fix trunk to work
> the way we want it to look. I think we should have LeafReader.postings() and
> TermsEnum.postings(), and everything should use PostingsEnum. This is
> simplest.
> But in 5.x, I think we should have DocsEnum and DocsAndPositionsEnum which
> are deprecated, to help guide the user.
> The "sugar" methods on LeafReader that exist in 5.0 (termDocsEnum(),
> termPositionsEnum()) should be deprecated (with message to use postings())
> and final, and can just wrap PostingsEnum. There is no reuse and flags here
> so this is very simple.
> On TermsEnum its more complicated, but i dont think impossible. We should add
> back deprecated and final termDocsEnum() and termPositionsEnum() (with
> message to use postings()) and these deprecated ones can have an instanceof
> check, unwrapping back to PostingsEnum before they invoke postings behind the
> scenes.
> For the 2 remaining ones on TermsEnum that take flags, thats the most tricky.
> I actually think we shouldn't change the existing constant values when we
> dont have to. And I don't think the names FLAG_FREQS are special, i'd rather
> these just be constants like FREQS. I looked thru JDK constants
> (http://docs.oracle.com/javase/7/docs/api/constant-values.html) and only one
> class uses this FLAG_xxx prefix.
> So I think we should have PostingsEnum.FREQS etc with new values, not
> conflicting with the old FLAG_FREQS etc values (which we can add back,
> deprecated, to DocsEnum and DocsAndPositionsEnum). We can even add a check to
> the deprecated methods that only valid values are passed.
> This just means we have contained back compat, only for deprecated and final
> sugar methods in LeafReader and TermsEnum, and the 2 deprecated classes. I
> think we can live with that and it would save users pain.
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