Robert Burke created BEAM-10169:
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Summary: ParDo* functions should declare the correct output N in
their error message
Key: BEAM-10169
URL: https://issues.apache.org/jira/browse/BEAM-10169
Project: Beam
Issue Type: Improvement
Components: sdk-go
Reporter: Robert Burke
User report noted the confusion in the error if you use a DoFn with 0 outputs
with beam.ParDo instead of beam.ParDo0.
In that case, a panic stack trace is followed by the cryptic: "expected 1
output. Found: []"
We can do better.
While we can't change the return signature dynamically (that's for ParDoN
only), we can instead clearly indicate:
* the DoFn in question.
* the number of outputs the DoFn has
* and recommend using ParDo0, ParDo, ParDo2,...ParDo7, or ParDoN, as
appropriate.
https://github.com/apache/beam/blob/master/sdks/go/pkg/beam/pardo.go#L361 would
need to change as well as any of the specific cases that follow.
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