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https://issues.apache.org/jira/browse/SPARK-27683?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16838548#comment-16838548
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Lukas Rytz commented on SPARK-27683:
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bq. This makes it hard to create an API method that works in both
Do you see a problem, in genral, if the 2.12 flatMap takes a {{T =>
TraversableOnce[U]}}, while the 2.13 API takes a {{T => IterableOnce[U]}}? I
think this should be the preferred solution. It might seems simpler if both
2.12 and 2.13 use the "same" type, e.g. {{scala.collection.Iterable}}, but in
reality they are not the same either, due to the collections rewrite, and due
to major-version-incompatibilities in general. And it would change / restrict
the API for no good reason.
Using {{TraversableOnce}} / {{IterableOnce}} can be achieved either with a type
alias, or by having separate source files for 2.12 and 2.13. As you mention,
there's already the {{scala.collection.compat.IterableOnce}} alias in the
compat library. Alternatively you can use the deprecated
{{scala.collection.TraversableOnce}} alias that exists in the 2.13 standard
library. Or you can define your own.
As far as I can see, the disadvantage of using an alias is that it shows up in
Scaladocs, the API, and in source code. So it's an indirection that users have
to go through when looking at the API. Version-specific source files would
avoid that.
> Remove usage of TraversableOnce
> -------------------------------
>
> Key: SPARK-27683
> URL: https://issues.apache.org/jira/browse/SPARK-27683
> Project: Spark
> Issue Type: Sub-task
> Components: ML, Spark Core, SQL, Structured Streaming
> Affects Versions: 3.0.0
> Reporter: Sean Owen
> Assignee: Sean Owen
> Priority: Major
>
> As with {{Traversable}}, {{TraversableOnce}} is going away in Scala 2.13. We
> should use {{IterableOnce}} instead. This one is a bigger change as there are
> more API methods with the existing signature.
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