[jira] [Created] (FLINK-2104) Fallback implicit values for PredictOperation and TransformOperation don't work if Nothing is inferred as the output type

[Shang Yuanchun (Jira)]

Till Rohrmann created FLINK-2104:
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             Summary: Fallback implicit values for PredictOperation and TransformOperation don't work if Nothing is inferred as the output type
                 Key: FLINK-2104
                 URL: https://issues.apache.org/jira/browse/FLINK-2104
             Project: Flink
          Issue Type: Bug
          Components: Machine Learning Library
            Reporter: Till Rohrmann
            Assignee: Till Rohrmann
             Fix For: 0.9


If one calls a {{Predictor}} or {{Transformer}} with a wrong input type, then the Scala compiler tries to apply the fallback implicit value for this operation type. However, since the return type of the operations is parameterized, it will infer it to be {{Nothing}}. The problem is then that the implicit value {{Operation[Self, Input, Nothing]}} cannot be unified with the implicit parameter {{Operation[Self, Input, Output]}}. This seems to be a known Scala issue [https://issues.scala-lang.org/browse/SI-1570].

I propose to fix the output type of the implicit values to {{Any}} which will avoid that {{Nothing}} is inferred. This should solve the problem.



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