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https://issues.apache.org/jira/browse/SPARK-28889?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16917152#comment-16917152
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Zachary S Ennenga commented on SPARK-28889:
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I think this change is pretty simple, planning to put together a PR myself
unless I hear there's a good reason why I shouldn't.
> Allow UDTs to define custom casting behavior
> --------------------------------------------
>
> Key: SPARK-28889
> URL: https://issues.apache.org/jira/browse/SPARK-28889
> Project: Spark
> Issue Type: Improvement
> Components: Spark Core
> Affects Versions: 2.4.3
> Reporter: Zachary S Ennenga
> Priority: Minor
>
> Looking at `org.apache.spark.sql.catalyst.expressions.Cast`, UDTs do not
> support any sort of casting except for identity casts, IE:
> {code:java}
> case (udt1: UserDefinedType[_], udt2: UserDefinedType[_]) if udt1.userClass
> == udt2.userClass =>
> true
> {code}
> I propose we add an additional piece of functionality here to allow UDTs to
> define their own canCast and cast functions to allow users to define their
> own cast mechanisms.
> An example of how this might look:
> {code:java}
> case (fromUDT: UserDefinedType[_], toUDT: UserDefinedType[_]) =>
> toUDT.canCast(fromUDT) // Returns boolean
> {code}
> {code:java}
> case (fromUDT: UserDefinedType[_], toUDT: UserDefinedType[_]) =>
> toUDT.cast(fromUDT) // Returns toUDT
> {code}
> The UDT base class would contain a default implementation that replicates
> current behavior (IE no casting).
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