Zachary S Ennenga created SPARK-28889:
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Summary: 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
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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