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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (BEAM-440) Create.values() returns a type-unsafe Coder
Date Thu, 09 Feb 2017 17:50:41 GMT

    [ https://issues.apache.org/jira/browse/BEAM-440?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15859897#comment-15859897
] 

ASF GitHub Bot commented on BEAM-440:
-------------------------------------

Github user asfgit closed the pull request at:

    https://github.com/apache/beam/pull/843


> Create.values() returns a type-unsafe Coder
> -------------------------------------------
>
>                 Key: BEAM-440
>                 URL: https://issues.apache.org/jira/browse/BEAM-440
>             Project: Beam
>          Issue Type: Bug
>          Components: sdk-java-core
>            Reporter: Daniel Halperin
>            Assignee: Jason White
>              Labels: backward-incompatible, newbie, starter
>
> {{Create.values()}} with no arguments will default to a {{VoidCoder}}, unless one is
set later with {{setCoder(Coder)}}.
> Although it will encode its input correctly, this seems like a bad choice in many cases.
E.g., with {{Flatten}}:
> {code}
>     PCollection<KV<SomeClass, Integer>> initial = p.apply("First", Create.<KV<SomeClass,
Integer>>of());
>     PCollection<KV<SomeClass, Integer>> second =
>         p.apply("Second", Create.of("a", "b")).apply(ParDo.of(new MyAvroDoFn()));
>     PCollectionList
>     .of(initial).and(second)
>         .apply(Flatten.<KV<SomeClass, Integer>>pCollections());
> {code}
> This crashes trying to cast a KV from "Second" to a Void.class.
> 1. Suggest throwing a warning in {{getDefaultOutputCoder}} when defaulting to {{VoidCoder}}
for an empty elements list. Should this be an error?
> 2. Suggest adding something like {{Create.empty(TypeDescriptor)}} to handle this case
properly.



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