[jira] [Commented] (FLINK-3042) Define a way to let types create their own TypeInformation

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-3042?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15468507#comment-15468507 ] 

ASF GitHub Bot commented on FLINK-3042:
---------------------------------------

Github user greghogan commented on a diff in the pull request:

    https://github.com/apache/flink/pull/2337#discussion_r77714875
  
    --- Diff: flink-core/src/main/java/org/apache/flink/api/common/typeinfo/TypeInformation.java ---
    @@ -122,14 +123,25 @@
     	public abstract Class<T> getTypeClass();
     
     	/**
    -	 * Returns the generic parameters of this type.
    +	 * Optional method for giving Flink's type extraction system information about the mapping
    +	 * of a generic type parameter to the type information of a subtype. This information is necessary
    +	 * in cases where type information should be deduced from an input type.
     	 *
    -	 * @return The list of generic parameters. This list can be empty.
    +	 * For instance, a method for a {@link Tuple2} would look like this:
    +	 * <code>
    +	 * Map m = new HashMap();
    +	 * m.put("T0", this.getTypeAt(0));
    +	 * m.put("T1", this.getTypeAt(1));
    +	 * return m;
    +	 * </code>
    +	 *
    +	 * @return map of inferred subtypes; it must not contain all generic parameters as key;
    --- End diff --
    
    What is meant by "it must not contain all generic parameters as key"?


> Define a way to let types create their own TypeInformation
> ----------------------------------------------------------
>
>                 Key: FLINK-3042
>                 URL: https://issues.apache.org/jira/browse/FLINK-3042
>             Project: Flink
>          Issue Type: Improvement
>          Components: Core
>    Affects Versions: 0.10.0
>            Reporter: Stephan Ewen
>            Assignee: Timo Walther
>             Fix For: 1.0.0
>
>
> Currently, introducing new Types that should have specific TypeInformation requires
>   - Either integration with the TypeExtractor
>   - Or manually constructing the TypeInformation (potentially at every place) and using type hints everywhere.
> I propose to add a way to allow classes to create their own TypeInformation (like a static method "createTypeInfo()").
> To support generic nested types (like Optional / Either), the type extractor would provide a Map of what generic variables map to what types (deduced from the input). The class can use that to create the correct nested TypeInformation (possibly by calling the TypeExtractor again, passing the Map of generic bindings).



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