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From "Stephan Ewen (JIRA)" <j...@apache.org>
Subject [jira] [Created] (FLINK-2788) Add type hint with TypeExtactor call on Hint Type
Date Tue, 29 Sep 2015 22:05:04 GMT
Stephan Ewen created FLINK-2788:
-----------------------------------

             Summary: 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
            Reporter: Stephan Ewen
             Fix For: 0.10


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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