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From "Grant Ingersoll (JIRA)" <>
Subject [jira] Commented: (LUCENE-1422) New TokenStream API
Date Tue, 21 Oct 2008 21:14:44 GMT


Grant Ingersoll commented on LUCENE-1422:

Yes I agree. But my take here is that the package-private methods are expert methods for which
we don't have to guarantee backwards-compatibility the same way we do for public and protected
APIs (i. e. only break compatibility in a version change X.Y->(X+1).0). Of course we have
to update all contribs.

I don't know about that.  I don't think it has been decided one way or the other.  At one
extreme, the policy says: "That's to say, any code developed against X.0 should continue to
run without alteration against all X.N releases. "  Since, it is perfectly legal to access
package methods by declaring oneself to be part of that package, and, since we don't sign
our jars to prevent such a move, I can see that others may feel free to use them when they
deem it beneficial.  On the other hand, convention/good programming style suggests it's not
good to write programs that rely on package level APIs in libraries, so caveat emptor.

I do note that we broke Luke once before when we changed something that was package scoped.
 Maybe a shame on us, maybe a shame on Luke,  I don't know.

That being said, I doubt a lot of people are doing this, so...  
I'd suggest a vote on it on dev if breaking it is decided on, like we did w/ Fieldable and
that we explicitly state what is happening in CHANGES, etc.  

Said vote could either be specific to this problem, or it could attempt to address the question
of whether package scoped things are subject to the back-compat. policy.

> New TokenStream API
> -------------------
>                 Key: LUCENE-1422
>                 URL:
>             Project: Lucene - Java
>          Issue Type: New Feature
>          Components: Analysis
>            Reporter: Michael Busch
>            Assignee: Michael Busch
>            Priority: Minor
>             Fix For: 2.9
>         Attachments: lucene-1422.patch, lucene-1422.take2.patch, lucene-1422.take3.patch,
> This is a very early version of the new TokenStream API that 
> we started to discuss here:
> This implementation is a bit different from what I initially
> proposed in the thread above. I introduced a new class called
> AttributedToken, which contains the same termBuffer logic 
> from Token. In addition it has a lazily-initialized map of
> Class<? extends Attribute> -> Attribute. Attribute is also a
> new class in a new package, plus several implementations like
> PositionIncrementAttribute, PayloadAttribute, etc.
> Similar to my initial proposal is the prototypeToken() method
> which the consumer (e. g. DocumentsWriter) needs to call.
> The token is created by the tokenizer at the end of the chain
> and pushed through all filters to the end consumer. The 
> tokenizer and also all filters can add Attributes to the 
> token and can keep references to the actual types of the
> attributes that they need to read of modify. This way, when
> boolean nextToken() is called, no casting is necessary.
> I added a class called TestNewTokenStreamAPI which is not 
> really a test case yet, but has a static demo() method, which
> demonstrates how to use the new API.
> The reason to not merge Token and TokenStream into one class 
> is that we might have caching (or tee/sink) filters in the 
> chain that might want to store cloned copies of the tokens
> in a cache. I added a new class NewCachingTokenStream that
> shows how such a class could work. I also implemented a deep
> clone method in AttributedToken and a 
> copyFrom(AttributedToken) method, which is needed for the 
> caching. Both methods have to iterate over the list of 
> attributes. The Attribute subclasses itself also have a
> copyFrom(Attribute) method, which unfortunately has to down-
> cast to the actual type. I first thought that might be very
> inefficient, but it's not so bad. Well, if you add all
> Attributes to the AttributedToken that our old Token class
> had (like offsets, payload, posIncr), then the performance
> of the caching is somewhat slower (~40%). However, if you 
> add less attributes, because not all might be needed, then
> the performance is even slightly faster than with the old API.
> Also the new API is flexible enough so that someone could
> implement a custom caching filter that knows all attributes
> the token can have, then the caching should be just as 
> fast as with the old API.
> This patch is not nearly ready, there are lot's of things 
> missing:
> - unit tests
> - change DocumentsWriter to use new API 
>   (in backwards-compatible fashion)
> - patch is currently java 1.5; need to change before 
>   commiting to 2.9
> - all TokenStreams and -Filters should be changed to use 
>   new API
> - javadocs incorrect or missing
> - hashcode and equals methods missing in Attributes and 
>   AttributedToken
> I wanted to submit it already for brave people to give me 
> early feedback before I spend more time working on this.

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