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https://issues.apache.org/jira/browse/LUCENE-5202?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13762011#comment-13762011
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Michael McCandless commented on LUCENE-5202:
--------------------------------------------

bq. I suspect that there's something that LTF does that I don't need that 
explains why it is so complex.

I think it's trying to support arbitrary lookahead, and insertion of new 
tokens.  Sort of what a SynonymFilter would need.

But it's obviously not easy to use yet :)
                
> LookaheadTokenFilter consumes an extra token in nextToken
> ---------------------------------------------------------
>
>                 Key: LUCENE-5202
>                 URL: https://issues.apache.org/jira/browse/LUCENE-5202
>             Project: Lucene - Core
>          Issue Type: Bug
>    Affects Versions: 4.3.1
>            Reporter: Benson Margulies
>         Attachments: LUCENE-5202.patch, LUCENE-5202.patch
>
>
> This is a bit hard to explain except by looking at the test case. I've coded 
> a filter that uses LookaheadTokenFilter. The incrementToken method peeks some 
> tokens. Then, it seems, nextToken in the Lookahead class calls peekToken 
> itself, which seems to me to consume a token so that it's not seen when the 
> derived class sets out to process the next set of tokens.
> In passing, this test case can be used to demonstrate that it does not work 
> to try to use the afterPosition method to set up attributes of the token that 
> we're 'after'. Probably that was never intended. However, I'm hoping for some 
> feedback as to whether the rest of the structure here is as intended for 
> subclasses of LookaheadTokenFilter.

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