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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-2788) Add type hint with TypeExtactor call on Hint Type
Date Tue, 01 Mar 2016 10:38:18 GMT

    [ https://issues.apache.org/jira/browse/FLINK-2788?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15173568#comment-15173568
] 

ASF GitHub Bot commented on FLINK-2788:
---------------------------------------

Github user StephanEwen commented on the pull request:

    https://github.com/apache/flink/pull/1744#issuecomment-190655939
  
    Good catch, I'll update the annotations.
    
    I would like to add a `returns(TypeHint)` method and deprecate the String variant in a
separate issue.


> Add type hint with TypeExtactor call on Hint Type
> -------------------------------------------------
>
>                 Key: FLINK-2788
>                 URL: https://issues.apache.org/jira/browse/FLINK-2788
>             Project: Flink
>          Issue Type: Improvement
>          Components: Core
>    Affects Versions: 0.10.0
>            Reporter: Stephan Ewen
>            Assignee: Stephan Ewen
>             Fix For: 1.0.0
>
>
> As per discussion with [~aljoscha]
> A very good and type safe way to supply type hints would be the following:
> Define a hint class that takes a generic parameter.
> {code}
> public abstract class TypeHint<T> {}
> {code}
> The hints would have the following method:
> {code}
> public DataSet<T> returns(TypeHint<T> hint);
> {code}
> It would be used like this:
> {code}
> DataSet<Sting> data = ...;
> data
>   .flatMap( (String str, Collector<Integer> out) -> out.collect(str.length())
)
>   .returns( new TypeHint<Integer>() {})
> {code}
> This would create an inline subclass of the hint, from which the type could be extracted.
The generics would ensure that it is typesafe.



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