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https://issues.apache.org/jira/browse/HADOOP-6486?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Doug Cutting updated HADOOP-6486:
---------------------------------
Status: Open (was: Patch Available)
> Why is EnumSetWritable now a collection?
Type erasure. Avro reflect knows how to infer a schema for any
Collection<Foo>, but not for an arbitrary Wrapper<Foo>. Consider, for example,
the following code:
{code}
...
private static class Wrapper<T> {
T wrapped;
}
private Wrapper<String> wrapper;
...
{code}
Java reflection does not make it easy for one to infer a schema for 'wrapper'.
The reflected type of that field is a ParametrizedType: Wrapper.class
parameterized by String.class. So one might then, to finding the schema for
Wrapper.class, pass down String.class as a parameter, use
Class#getTypeParameters() to bind T to String.class, then, when T is referenced
in the type of the field "wrapped", lookup that binding. I worry about scope
issues, since the name T is scoped lexically, while walking the class structure
is not, but perhaps that's not an issue. So perhaps Avro reflect could
correctly determine a schema for "wrapper", but, at present, it does not.
Also, representing EnumSetWritable as an array of enum values rather than a
one-field-class that wraps an array of enum values seems like a better schema.
> fix common classes to work with Avro 1.3 reflection
> ---------------------------------------------------
>
> Key: HADOOP-6486
> URL: https://issues.apache.org/jira/browse/HADOOP-6486
> Project: Hadoop Common
> Issue Type: Improvement
> Components: ipc
> Reporter: Doug Cutting
> Assignee: Doug Cutting
> Fix For: 0.22.0
>
> Attachments: HADOOP-6486.patch, HADOOP-6486.patch, HADOOP-6486.patch,
> HADOOP-6486.patch, HADOOP-6486.patch, HADOOP-6486.patch, HADOOP-6486.patch
>
>
> A few minor changes are required to get some common classes to work correctly
> with Avro 1.3 reflection.
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