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https://issues.apache.org/jira/browse/FLINK-2899?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15258588#comment-15258588
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Greg Hogan commented on FLINK-2899:
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Is this due to a limitation of {{TypeExtractor.createTypeInfo}} or the lack of
parameterization in user code?
The {{TypeInformation}} is extracted from {{NeighborsFunctionWithVertexValue<K,
TreeMap<K, Integer>, NullValue, Vertex<K, K>>}} with
{{TypeExtractor.createTypeInfo(NeighborsFunctionWithVertexValue.class,
function.getClass(), 3, null, null)}} (link 0).
The function is instantiated with {{new PropagateNeighborValues()}}, so no
parameterization. Does this limit what {{TypeExtractor}} can extract?
I agree with [~Zentol] that if {{ApplyNeighborCoGroupFunction}} is extracting
{{TypeInformation}} then accepting this as a function parameter looks
superfluous.
0:
[https://github.com/andralungu/flink/commit/1fbc09ca35e80f61f31cf7a6166f27f2a6f142c1#diff-e2c6679629dbf39dbd9ba785d1516f2cR188]
1:
[https://github.com/andralungu/flink/commit/1fbc09ca35e80f61f31cf7a6166f27f2a6f142c1#diff-e2c6679629dbf39dbd9ba785d1516f2cR96]
> The groupReduceOn* methods which take types as a parameter fail with
> TypeErasure
> --------------------------------------------------------------------------------
>
> Key: FLINK-2899
> URL: https://issues.apache.org/jira/browse/FLINK-2899
> Project: Flink
> Issue Type: Bug
> Components: Gelly
> Affects Versions: 0.10.0
> Reporter: Andra Lungu
>
> I tried calling groupReduceOnEdges (EdgesFunctionWithVertexValue<K, VV, EV,
> T> edgesFunction, EdgeDirection direction, TypeInformation<T> typeInfo) in
> order to make the vertex-centric version of the Triangle Count library method
> applicable to any kind of key and I got a TypeErasure Exception.
> After doing a bit of debugging (see the hack in
> https://github.com/andralungu/flink/tree/trianglecount-vertexcentric), I saw
> that actually the call to
> TypeExtractor.createTypeInfo(NeighborsFunctionWithVertexValue.class, .... in
> ApplyNeighborCoGroupFunction does not work properly, i.e. it returns null.
> From what I see, the coGroup in groupReduceOnNeighbors tries to infer a type
> before "returns" is called.
> I may be missing something, but that particular feature (groupReduceOn with
> types) is not documented or tested so we would also need some tests for that.
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