David Whiting created CRUNCH-585:
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Summary: Move Java 8 lambda support into separate module
Key: CRUNCH-585
URL: https://issues.apache.org/jira/browse/CRUNCH-585
Project: Crunch
Issue Type: Improvement
Reporter: David Whiting
Fix For: 0.14.0
Attachments: 0001-Java-8-lambda-support-for-Apache-Crunch.patch
As discussed on a previous dev list thread, this patch implements a set of
operations to conveniently use Java 8 lambda expressions and method references
to construct Crunch pipelines by wrapping the PCollection instances into
analogous "LCollection" instances which delegate the necessary operations, in
much the same way the Scrunch wraps the Crunch Core API.
I'm still not 100% convinced that this is better for the user than the existing
lambda support via IMapFn and IDoFn PCollection operations, so I'm still
interested in people's views on this.
Advantages:
- Concise self-contained implementation
- Methods implemented in terms of a very basic subset of PCollection operations
(useful if we want to scale down the PCollection API at some point)
- API can be written in terms of the Java 8 library, operating on streams and
functional interfaces, making in more familiar to a new developer.
- Retain "type '.' and see what I can do" experience.
- Really easy to add new operations (just default method on interface)
Disadvantages:
- PCollections must be wrapped into LCollections before use.
- LCollections must be unwrapped into PCollections to access some existing
operations.
- Using counters and other contextual data is far more complex.
Some limitations of this particular patch:
- Some omissions in API (not sure how much to implement)
- No Javadocs yet.
- Very poor tests.
- Naming is a bit off (eg. reduce() or reduceValues(), get() or underlying())
I can fix all that, but I wanted to bring the community in at this point to get
some feedback on both the idea and the implementation as it's quite a big patch.
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