[jira] [Commented] (KAFKA-3519) Refactor Transformer templates to return the same strong-typed value.

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-3519?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15232454#comment-15232454 ] 

ASF GitHub Bot commented on KAFKA-3519:
---------------------------------------

GitHub user guozhangwang opened a pull request:

    https://github.com/apache/kafka/pull/1204

    KAFKA-3519: Refactor Transformer's transform / punctuate to return nullable values

    

You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/guozhangwang/kafka KTransformR

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/kafka/pull/1204.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 #1204
    
----

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> Refactor Transformer templates to return the same strong-typed value.
> ---------------------------------------------------------------------
>
>                 Key: KAFKA-3519
>                 URL: https://issues.apache.org/jira/browse/KAFKA-3519
>             Project: Kafka
>          Issue Type: Bug
>          Components: streams
>            Reporter: Guozhang Wang
>            Assignee: Guozhang Wang
>              Labels: api
>             Fix For: 0.10.0.0
>
>
> Currently the Transformer interface's template is:
> {code}
> R transform(K key, V value);
> {code}
> While all its usage requires a key-value pair, and hence constructing the object as:
> {code}
> new Transformer<K, V, KeyValue<K1, V1>>
> {code}
> Since we expect Transformer to be only used in the Streams DSL, which is supposed to return another key-value pair streams, it's better to define its template just as
> {code}
> public interface Transformer<K, V, K1, V1> {
>     KeyValue<K1, V1> transform(K key, V value);
> }
> {code}
> Also, we can allow punctuate() to also return a nullable KeyValue<K1, V1> pair, and let the implementation to forward to downstream processor only when the returned pair is not null.



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