[jira] [Commented] (SPARK-8653) Add constraint for Children expression for data type

["Davies Liu (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-8653?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14609579#comment-14609579 ] 

Davies Liu commented on SPARK-8653:
-----------------------------------

[~rxin] With the new `ExpectsInputTypes`, we still need a way to tell how to do the conversion, it's ugly to do the type switch in eval() or codegen().

Maybe we could improve `AutoCastInputType` to have a method `acceptedTypes`, which returns a list of list of data types, specify those types could be casted into expected types. Be default, it will accept all type types which could be casted to expected types. 

> Add constraint for Children expression for data type
> ----------------------------------------------------
>
>                 Key: SPARK-8653
>                 URL: https://issues.apache.org/jira/browse/SPARK-8653
>             Project: Spark
>          Issue Type: Sub-task
>          Components: SQL
>            Reporter: Cheng Hao
>
> Currently, we have trait in Expression like `ExpectsInputTypes` and also the `checkInputDataTypes`, but can not convert the children expressions automatically, except we write the new rules in the `HiveTypeCoercion`.



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