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https://issues.apache.org/jira/browse/FLINK-18683?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Timo Walther closed FLINK-18683.
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    Fix Version/s: 1.12.0
       Resolution: Fixed

Fixed in 1.12.0: 3fd1f64e6bd5d6b0729484a0999ba12be99e364b

> Support @DataTypeHint for TableFunction output types
> ----------------------------------------------------
>
>                 Key: FLINK-18683
>                 URL: https://issues.apache.org/jira/browse/FLINK-18683
>             Project: Flink
>          Issue Type: Sub-task
>          Components: Table SQL / API
>            Reporter: Fabian Hueske
>            Assignee: Timo Walther
>            Priority: Minor
>              Labels: pull-request-available
>             Fix For: 1.12.0
>
>
> For ScalarFunctions, the return type of an eval method can be declared with a 
> {{@DataTypeHint}}:
> {code:java}
> @DataTypeHint("INT")
> public Integer eval(Integer value) {
>   return value * 2;
> }{code}
> This does not work for TableFunctions because the {{@DataTypeHint}} 
> annotation refers to the {{void}} return type. Hence, {{TableFunction}} 
> {{eval()}} methods must always be annotated with the more complex 
> {{@FunctionHint}} method.
> However, I think that context, it is clear that the {{@DataTypeHint}} 
> annotation refers to the actual return type of the table function (the type 
> parameter of {{TableFunction<OUT>}}).
> We could consider allowing {{@DataTypeHint}} annotations also on 
> {{TableFunction}} classes (defining the output type of all eval methods) and 
> {{eval()}} methods.



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