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https://issues.apache.org/jira/browse/FLINK-2104?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14562676#comment-14562676
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ASF GitHub Bot commented on FLINK-2104:
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GitHub user tillrohrmann opened a pull request:
https://github.com/apache/flink/pull/741
[FLINK-2104] [ml] Fixes problem with type inference for fallback implicits
The solution seems to be to fix the output type to `Any`. This has the
consequence that all following operations will also be fallback operations if
they don't support `Any` inputs. But this should be fine since only the first
fallback operation will throw an exception stating why the operator could not
find a suitable operation.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/tillrohrmann/flink fixFallbackImplicits
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/flink/pull/741.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #741
----
commit 48d3003036a0d049b73fd40278a1470b99f87c2b
Author: Till Rohrmann <[email protected]>
Date: 2015-05-27T18:08:19Z
[FLINK-2104] [ml] Fixes problem with type inference for fallback implicits
where Nothing is not correctly treated (see SI-1570)
----
> 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
> Labels: ML
> 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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