What is it?

A tiny interoperability library for passing JRuby/Scala collections back and forth.

https://rubygems.org/gems/jruby-scala-collections

Installation

$ gem install jruby-scala-collections

How do you use it?

Each Object has two methods: #to_scala and #from_scala. These can be used to wrap JRuby/Scala collections.

Example:

gem 'jruby-scala-collections'
require 'jruby/scala_support'

r_arr = [1,2,3,4]
scala_arr = scala_object.do_stuff(r_arr.to_scala)
scala_arr.from_scala

• Array#to_scala becomes scala.collection.mutable.Buffer
• Hash#to_scala becomes scala.collection.mutable.Map
• Set#to_scala becomes scala.collection.mutable.Set

Take node that even collections inside collections are wrapped:

> a = [1,[2,3],{4=>5}].to_scala
 => #<Java::JrubyCollection::ListWrapper:0x768bdb> 
> a.apply(1)
 => #<Java::JrubyCollection::ListWrapper:0x884ab9> 
> a.apply(2)
 => #<Java::JrubyCollection::MapWrapper:0x1bb605> 

From Scala side Ruby primitives are converted using default JRuby conversions that are listed in https://github.com/jruby/jruby/wiki/CallingJavaFromJRuby section "Conversion of Types".

So if you expect Array of Fixnums coming to your scala method, it should accept:

// Either
def scalaMethod(args: collection.mutable.Buffer[Long])
// Or
def scalaMethod(args: collection.Seq[Long])

It also adds #Some and None so you could pass values to Scala methods:

scala_object.set(Some(3))
scala_object.get(None)

Disclaimer

This library was written by Artūras 'arturaz' Šlajus for personal usage. #to_scala should work pretty well, however Ruby wrappers may be missing methods. Patches are welcome.