Luke Hutchison created FLINK-6114:
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Summary: Type checking fails with generics, even when concrete
type of field is not needed
Key: FLINK-6114
URL: https://issues.apache.org/jira/browse/FLINK-6114
Project: Flink
Issue Type: Bug
Affects Versions: 1.2.0
Reporter: Luke Hutchison
The Flink type checker does not allow generic types to be used in any field of
a tuple when a join is being executed, even if the generic is not in a field
that is involved in the join.
I have a type Tuple3<String, K, Float>, which contains a generic type parameter
K. I am joining using .where(0).equalTo(0). The type of field 0 is well-defined
as String. However, this gives me the following error:
{noformat}
Exception in thread "main"
org.apache.flink.api.common.functions.InvalidTypesException: Type of
TypeVariable 'K' in 'public static org.apache.flink.api.java.DataSet
mypkg.MyClass.method(params)' could not be determined. This is most likely a
type erasure problem. The type extraction currently supports types with generic
variables only in cases where all variables in the return type can be deduced
from the input type(s).
at
org.apache.flink.api.java.typeutils.TypeExtractor.createSubTypesInfo(TypeExtractor.java:989)
{noformat}
The code compiles fine, however -- the static type system is able to correctly
resolve the types in the surrounding code.
Really only the fields that are affected by joins (or groupBy, aggregation
etc.) should be checked for concrete types in this way.
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