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https://issues.apache.org/jira/browse/LUCENE-9696?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17272129#comment-17272129
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Michael McCandless commented on LUCENE-9696:
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Thanks [~gus]! We could separately consider adding group support to FSTs and
to Lucene's {{Automaton}} classes, which are two separate implementations of
fun finite-state algorithms.
> RegExp with group references
> ----------------------------
>
> Key: LUCENE-9696
> URL: https://issues.apache.org/jira/browse/LUCENE-9696
> Project: Lucene - Core
> Issue Type: Wish
> Reporter: Gus Heck
> Priority: Minor
>
> PatternTypingFilter presently relies on java util regexes, but LUCENE-7465
> found performance benefits using our own RegExp class instead. Unfortunately
> RegExp does not currently report matching subgroups which is key to
> PatternTypingFilter's use (and probably useful in other endeavors as well).
> What's needed is reporting of sub-groups such that
> new RegExp("(foo(.+)")) -->> converted to run atomaton etc --> match found
> for "foobar" --> somehow reports getGroup(1) as "bar"
> And getGroup() can be called on some object reasonably accessible to the code
> using RegExp in the first place.
> Clearly there's a lot to be worked out there since the normal usage pattern
> converts things to a DFA / run Automaton etc, and subgroups are not a natural
> concept for those classes. But if this could be achieved without loosing the
> performance benefits, that would be interesting :).
> Opening this Wish ticket as encouraged by [~mikemccand] in LUCENE-9575. I
> won't be able to work on it any time soon to encourage anyone else interested
> to pick it up or to drop links or ideas in here.
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