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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-3042) Define a way to let types create their own TypeInformation
Date Thu, 08 Sep 2016 10:49:20 GMT

    [ https://issues.apache.org/jira/browse/FLINK-3042?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15473535#comment-15473535
] 

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

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

    https://github.com/apache/flink/pull/2337#discussion_r77984002
  
    --- Diff: flink-core/src/main/java/org/apache/flink/api/java/typeutils/TypeExtractor.java
---
    @@ -792,12 +832,40 @@ else if (t instanceof Class) {
     
     		return null;
     	}
    -	
    +
    +	@SuppressWarnings({"unchecked", "rawtypes"})
     	private <IN1> TypeInformation<?> createTypeInfoFromInput(TypeVariable<?>
returnTypeVar, ArrayList<Type> inputTypeHierarchy, Type inType, TypeInformation<IN1>
inTypeInfo) {
     		TypeInformation<?> info = null;
    -		
    +
    +		// use a factory to find corresponding type information to type variable
    +		final ArrayList<Type> factoryHierarchy = new ArrayList<>(inputTypeHierarchy);
    +		final TypeInfoFactory<?> factory = getClosestFactory(factoryHierarchy, inType);
    +		if (factory != null) {
    +			// the type that defines the factory is last in factory hierarchy
    +			final Type factoryDefiningType = factoryHierarchy.get(factoryHierarchy.size() - 1);
    +			// defining type has generics, the factory need to be asked for a mapping of subtypes
to type information
    +			if (factoryDefiningType instanceof ParameterizedType) {
    --- End diff --
    
    Yes, because we try to create type information from the input in this method. This only
works if a type variable connects input with output. `Map<InType<A>, OutType<A>>`


> 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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