Thanks Josh, will give this a try
On Wed, Nov 14, 2012 at 9:54 PM, Josh Wills <[email protected]> wrote: > I'm always glad to help people to extend Crunch in ways that are useful for > them. I think that most things that involve type-related extensions can be > handled using the PTypes.derived() function, which can be used to create > custom PTypes that are mapped to underlying serialized types, so that you > could do something like > > // Forgive my syntax errors, I'm doing this w/o an IDE > PType<Object> objectType = PTypes.derived(Object.class, new > InputMapFn<BytesWritable, Object>(), new OutputMapFn<Object, > BytesWritable>(), Writables.writables(BytesWritable.class)); > > ...which is essentially how Scrunch works: the PTypes { } functionality in > Scrunch maps from Scala types to Java types using the derived > functionality. > > The Converter stuff is internal to Avro and Writable, I can't think of a > case where that would need to be exposed outside the package (i.e., once > you've decided on whether to use Writables or Avro as your serialization > framework, the choice of Converter is fixed.) > > If you have a use case where the derived type can't handle the conversion > or is a poor choice for whatever reason, I'm all about having a discussion > and trying out different designs. > > Josh > > > On Wed, Nov 14, 2012 at 6:18 PM, Victor Iacoban <[email protected] > >wrote: > > > Hi, > > > > I'm very interested in writing a wrapper library around Apache Crunch for > > Clojure, something similar to existing Scrunch. > > How do you recommend to start? > > > > I was looking through Crunch code and it looks like I can pretty easily > > integrate it in clojure by adding some custom WritableType type. > > Something like WritableType<Object, ByteWritable> with a custom converter > > or inputFn/outputFn functions. > > > > Regretfully there are several issues with this approach and instead I'd > > have to duplicate all those type classes for a new type set > > * WritableType has a package visible constructor so I cannot extend it > and > > cannot instantiate it > > * Converter is instantiated inside WritableType constructor so in case I > > need a different converter I'm stuck > > * Writables has a factory method for WritableType but it's private > > * it looks like there is an attempt to support additional WritableTypes > > through EXTENSIONS in Writables but it would only work for cases where in > > WritableType<T, W> both T and W are hadoop writables > > > > So what do you think is a best solution, is it possible to open up the > api > > to support custom WritableTypes or the only option for me is to > implement a > > new ClojurePType and all related classes? > > > > Hope I'm not too detailed, but at this stage you all are probably very > > familiar with the code > > > > Thanks, > > Victor > > >
