[GitHub] flink pull request #2337: [FLINK-3042] [FLINK-3060] [types] Define a way to ...

[greghogan <gi...@git.apache.org>]

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"?


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