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https://issues.apache.org/jira/browse/BEAM-8612?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Tianyang Hu resolved BEAM-8612.
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Fix Version/s: Not applicable
Resolution: Fixed
> Convert []beam.T to the underlying type []T when passed to a DoFn with
> universal typed (beam.X) input
> -----------------------------------------------------------------------------------------------------
>
> Key: BEAM-8612
> URL: https://issues.apache.org/jira/browse/BEAM-8612
> Project: Beam
> Issue Type: New Feature
> Components: sdk-go
> Reporter: Tianyang Hu
> Assignee: Tianyang Hu
> Priority: Minor
> Fix For: Not applicable
>
> Time Spent: 1h
> Remaining Estimate: 0h
>
> Say there are two DoFn: f1, f2.
> - f1 declares the output type as []beam.T, and each element has the
> underlying type int.
> - f2 declares the input type as []int
> Passing f1 output to f2 works well. The conversion from []beam.T to []int
> happens at:
> https://github.com/apache/beam/blob/c7be0643934a87d73483cf1fd3199a425508b03c/sdks/go/pkg/beam/core/runtime/exec/fullvalue.go#L108
> But it doesn't work if f2 declares the input type as beam.X and type casts it
> to []int. This is because there's no type conversion when passing []beam.T to
> beam.X.
> We may consider supporting the above case by converting []beam.T to the
> underlying type []T when it's passed to a universal type.
> An issue is that if []beam.T is nil or empty, we don't know its underlying
> element type (unless we know which concrete type beam.T or beam.X is bound
> to, but this mapping doesn't seem to be kept at runtime?). In such case, we
> have to pass []beam.T to beam.X as is.
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