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https://issues.apache.org/jira/browse/LUCENE-5207?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13767523#comment-13767523
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Robert Muir commented on LUCENE-5207:
-------------------------------------
Uwe: can we defer that function stuff to another issue?
The whole discussion about classloader stuff doesnt make a lot of sense to me.
Today Functions are implemented with just normal invokeVirtual. Bindings aren't
used until you actually run the query... Today the way an expression interacts
with the Bindings is *not* with invokeVirtual, its just another valuesource
coming in to its array at runtime.
So I dont think custom functions should go thru Bindings, its totally unrelated
to how that class works at all. I also don't want to make the API very
confusing just because solr does crazy things with classloaders quite yet: I
think this is very close to usable for lucene users as-is.
> lucene expressions module
> -------------------------
>
> Key: LUCENE-5207
> URL: https://issues.apache.org/jira/browse/LUCENE-5207
> Project: Lucene - Core
> Issue Type: New Feature
> Reporter: Ryan Ernst
> Attachments: LUCENE-5207.patch
>
>
> Expressions are geared at defining an alternative ranking function (e.g.
> incorporating the text relevance score and other field values/ranking
> signals). So they are conceptually much more like ElasticSearch's scripting
> support (http://www.elasticsearch.org/guide/reference/modules/scripting/)
> than solr's function queries.
> Some additional notes:
> * In addition to referring to other fields, they can also refer to other
> expressions, so they can be used as "computed fields".
> * You can rank documents easily by multiple expressions (its a SortField at
> the end), e.g. Sort by year descending, then some function of score price and
> time ascending.
> * The provided javascript expression syntax is much more efficient than using
> a scripting engine, because it does not have dynamic typing (compiles to
> .class files that work on doubles). Performance is similar to writing a
> custom FieldComparator yourself, but much easier to do.
> * We have solr integration to contribute in the future, but this is just the
> standalone lucene part as a start. Since lucene has no schema, it includes an
> implementation of Bindings (SimpleBindings) that maps variable names to
> SortField's or other expressions.
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