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https://issues.apache.org/jira/browse/LUCENE-6879?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Uwe Schindler resolved LUCENE-6879.
-----------------------------------
Resolution: Fixed
Assignee: Uwe Schindler
Thanks for review!
> Allow to define custom CharTokenizer using Java 8 Lambdas/Method references
> ---------------------------------------------------------------------------
>
> Key: LUCENE-6879
> URL: https://issues.apache.org/jira/browse/LUCENE-6879
> Project: Lucene - Core
> Issue Type: Improvement
> Components: modules/analysis
> Affects Versions: Trunk
> Reporter: Uwe Schindler
> Assignee: Uwe Schindler
> Labels: Java8
> Fix For: Trunk
>
> Attachments: LUCENE-6879.patch, LUCENE-6879.patch
>
>
> As a followup from LUCENE-6874, I thought about how to generate custom
> CharTokenizers wthout subclassing. I had this quite often and I was a bit
> annoyed, that you had to create a subclass every time.
> This issue is using the pattern like ThreadLocal or many collection methods
> in Java 8: You have the (abstract) base class and you define a factory method
> named {{fromXxxPredicate}} (like {{ThreadLocal.withInitial(() -> value}}).
> {code:java}
> public static CharTokenizer
> fromTokenCharPredicate(java.util.function.IntPredicate predicate)
> {code}
> This would allow to define a new CharTokenizer with a single line statement
> using any predicate:
> {code:java}
> // long variant with lambda:
> Tokenizer tok = CharTokenizer.fromTokenCharPredicate(c ->
> !UCharacter.isUWhiteSpace(c));
> // method reference for separator char predicate + normalization by
> uppercasing:
> Tokenizer tok =
> CharTokenizer.fromSeparatorCharPredicate(UCharacter::isUWhiteSpace,
> Character::toUpperCase);
> // method reference to custom function:
> private boolean myTestFunction(int c) {
> return (cracy condition);
> }
> Tokenizer tok = CharTokenizer.fromTokenCharPredicate(this::myTestFunction);
> {code}
> I know this would not help Solr users that want to define the Tokenizer in a
> config file, but for real Lucene users this Java 8-like way would be easy and
> elegant to use. It is fast as hell, as it is just a reference to a method and
> Java 8 is optimized for that.
> The inverted factories {{fromSeparatorCharPredicate()}} are provided to allow
> quick definition without lambdas using method references. In lots of cases,
> like WhitespaceTokenizer, predicates are on the separator chars
> ({{isWhitespace(int)}}, so using the 2nd set of factories you can define them
> without the counter-intuitive negation. Internally it just uses
> {{Predicate#negate()}}.
> The factories also allow to give the normalization function, e.g. to
> Lowercase, you may just give {{Character::toLowerCase}} as
> {{IntUnaryOperator}} reference.
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