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https://issues.apache.org/jira/browse/FLINK-6866?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16065091#comment-16065091
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SmedbergM commented on FLINK-6866:
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A Map[K,V] is already Serializable, as is java.util.Map<K,V> -- it's just that
before 2.12 scala.collection.convert.Wrappers.MapWrapper didn't inherit from
the Serializable interface. I'm not sure there's a non-hacky (i.e. explicitly
checking whether the classname begins with scala.collections.convert) way to
get around this, because ObjectOutputStream checks whether each field inherits
from Serializable. Unfortunately, the scala library writers didn't give the
MapWrapper public access to its underlying wrapped Map.
I don't think the details of the particular code that we encountered this in is
all that relevant; in Scala, it's idiomatic to create immutable Maps and call
`.asJava` on them when a library (like Flink) requires a java.util.Map. Of
course, one can avoid having the wrapper by directly constructing the
java.util.Map as in the MWE, but then one has all the mutability and
concurrency worries that good idiomatic Scala lets me not think about.
> ClosureCleaner.clean fails for scala's JavaConverters wrapper classes
> ---------------------------------------------------------------------
>
> Key: FLINK-6866
> URL: https://issues.apache.org/jira/browse/FLINK-6866
> Project: Flink
> Issue Type: Bug
> Components: DataStream API, Scala API
> Affects Versions: 1.2.0, 1.3.0
> Environment: Scala 2.10.6, Scala 2.11.11
> Does not appear using Scala 2.12
> Reporter: SmedbergM
>
> MWE: https://github.com/SmedbergM/ClosureCleanerBug
> MWE console output:
> https://gist.github.com/SmedbergM/ce969e6e8540da5b59c7dd921a496dc5
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