Kenneth Knowles created BEAM-659:
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Summary: WindowFn#isCompatible should provide a meaningful reason
Key: BEAM-659
URL: https://issues.apache.org/jira/browse/BEAM-659
Project: Beam
Issue Type: Bug
Components: sdk-java-core
Reporter: Kenneth Knowles
Priority: Minor
{{WindowFn#isCompatible(...)}} returns a true/false answer without any
explanation of why; it suffers from a form of [boolean
blindness|https://existentialtype.wordpress.com/2011/03/15/boolean-blindness/].
We alleviated this for {{Coder#isDeterministic()}} by switching to
{{Coder#verifyDeterministic()}} which can raise an exception describing why it
is not deterministic (it could just as easily have been a return value).
We should do the same for {{WindowFn#isCompatible(...)}}.
See here:
http://stackoverflow.com/questions/39617897/inputs-to-flatten-had-incompatible-window-windowfns-when-cogroupbykey-with-calen
(a decent {{toString}} would go a long way, for immediate and trivial
improvement)
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