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From "David Whiting (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CRUNCH-585) Move Java 8 lambda support into separate module
Date Sun, 27 Dec 2015 09:32:49 GMT
David Whiting created CRUNCH-585:
------------------------------------

             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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