[jira] [Commented] (KAFKA-7714) Scala streams API should use Options in left and outer joins

["John Roesler (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-7714?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16713305#comment-16713305 ] 

John Roesler commented on KAFKA-7714:
-------------------------------------

Hi [~ccrain_kuka],

Thanks for your interest in improving the API!

I actually kicked around the idea of proposing a similar change for the Java API, partly for the same reason that Scala introduced `Option`, and partly because it gets us out of a semantic trap regarding the interpretation of records with `null` values.

It will probably be a minefield, but I wonder if we should at least consider making the change in both the Java and Scala APIs...

 

To answer your question about breaking changes... We try really hard to avoid it.

We've learned that sometimes, the syntax of Scala makes it impossible to make some changes without breaking source compatibility (notably implicits), but I think the change you're proposing would be possible to do "safely".

I think we'd introduce a new method with a default implementation calling back to the old method, and then mark the old method deprecated. To avoid forcing people to implement the deprecated method, we can also add a default implementation to it that throws an exception. It's a bummer, because the interface doesn't advertise that you have to implement a method, though, so I'm open to suggestions...

 

To actually propose a change, you have to go through the KIP process. I'm happy to help guide you through the process if you'd like.

-John

> Scala streams API should use Options in left and outer joins
> ------------------------------------------------------------
>
>                 Key: KAFKA-7714
>                 URL: https://issues.apache.org/jira/browse/KAFKA-7714
>             Project: Kafka
>          Issue Type: Improvement
>          Components: streams
>    Affects Versions: 2.0.1, 2.1.0
>            Reporter: Charles Crain
>            Priority: Minor
>
> The Scala streams DSL for left and outer joins should use Options instead of possibly-null parameters to the joiner functions. As currently written, implementers of joiners for Kafka Streams must account for the right side of a left join (or either side of an outer join) being null, which is not idiomatic Scala.
> Note to reviewer: I would like to contribute this change myself. What is the policy on breaking API changes? Would it be acceptable to change the left/outer join APIs to accept options? Or would I need to implement parallel versions (naming suggestions if so?).



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