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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 01:01:39 GMT

    [ https://issues.apache.org/jira/browse/BEAM-440?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15858803#comment-15858803
] 

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

    Be sure to do all of the following to help us incorporate your contribution
    quickly and easily:
    
     - [ ] Make sure the PR title is formatted like:
       `[BEAM-<Jira issue #>] Description of pull request`
     - [ ] Make sure tests pass via `mvn clean verify`. (Even better, enable
           Travis-CI on your fork and ensure the whole test matrix passes).
     - [ ] Replace `<Jira issue #>` in the title with the actual Jira issue
           number, if there is one.
     - [ ] If this contribution is large, please file an Apache
           [Individual Contributor License Agreement](https://www.apache.org/licenses/icla.txt).
    
    ---
    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 <jason.white@shopify.com>
Date:   2016-08-16T23:35:47Z

    add Create#empty

commit 65818bb0daf81826a015ce1008a0891491fab818
Author: Thomas Groh <tgroh@google.com>
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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