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From "Zachary S Ennenga (Jira)" <j...@apache.org>
Subject [jira] [Updated] (SPARK-28889) Allow UDTs to define custom casting behavior
Date Tue, 27 Aug 2019 23:52:00 GMT

     [ https://issues.apache.org/jira/browse/SPARK-28889?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Zachary S Ennenga updated SPARK-28889:
--------------------------------------
    Component/s:     (was: Spark Core)
                 SQL

> 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: SQL
>    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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