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https://issues.apache.org/jira/browse/KAFKA-4481?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15716152#comment-15716152
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ASF GitHub Bot commented on KAFKA-4481:
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GitHub user xvrl opened a pull request:
https://github.com/apache/kafka/pull/2205
KAFKA-4481: relax streams api type contraints
Make appropriate methods contravariant in key and value types.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/xvrl/kafka streams-contravariance
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/kafka/pull/2205.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #2205
----
commit 5ec27267d9714dd861b53e116cc1667c84ddcfd6
Author: Xavier Léauté <xav...@confluent.io>
Date: 2016-12-02T19:50:36Z
KAFKA-4481: relax streams api type contraints
Make appropriate methods contravariant in key and value types.
----
> Relax Kafka Streams API type constraints
> ----------------------------------------
>
> Key: KAFKA-4481
> URL: https://issues.apache.org/jira/browse/KAFKA-4481
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Reporter: Xavier Léauté
> Assignee: Xavier Léauté
> Labels: usability
>
> Streams API methods that apply transformations to streams are currently
> invariant in the key and value types, when they should probably be
> contravariant in those types.
> For instance, {{KStream.filter(Predicate<K, V> predicate)}} should be
> {{KStream.filter(Predicate<? super K, ? super V> predicate)}} to accept
> predicates that can act on any supertype of K, or V.
> Same thing applies to method that take {{Aggregator}}s,
> {{StreamPartitioner}}s, {{KeyValueMapper}}s, {{ValueMapper}}s,
> {{ProcessorSupplier}}s, {{ValueJoiner}}s, etc.
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