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https://issues.apache.org/jira/browse/BEAM-440?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15858803#comment-15858803
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ASF GitHub Bot commented on BEAM-440:
-------------------------------------
GitHub user tgroh opened a pull request:
https://github.com/apache/beam/pull/1957
[BEAM-440] Add Create#empty
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---
This replaces #843, which appears to be abandoned.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/tgroh/beam create_empty
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/beam/pull/1957.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 #1957
----
commit 9d9080a97050712845a31b777d1f739602e09e43
Author: Jason White <[email protected]>
Date: 2016-08-16T23:35:47Z
add Create#empty
commit 65818bb0daf81826a015ce1008a0891491fab818
Author: Thomas Groh <[email protected]>
Date: 2017-02-09T00:56:49Z
Replace Create.of(T...) with Create.of(T, T...)
This ensures that an empty Create must go through either
Create.empty(Coder) or Create.of(Iterable<T>). Enforce the non-emptiness
of the elements iterable with no coder.
----
> 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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