Question

I know there is ongoing work for in this regards but what is the exact status of JRUby 1.3 compatibility with Ruby 1.9.1 ? I am slightly confused if I can dwnload jruby 1.3 and start working with my ruby 1.9 installation.

The JRuby homepage says :
* Ruby 1.8.6 compatible now
* Ruby 1.9 compatible soon

Wikipedia says the following:

Release history

This table present only releases that present significant steps in JRuby history, aside from versions that mainly fixed bugs and improved performance.
Release Release Date Highlights
0.9 2006-08-01 Rails support[11]
1.1 2008-03-28 Performs better than Ruby MRI 1.8.7[6]
AOT mode and JIT mode[21]
1.1.4 2008-08-28 Refactored Java integration layer
Beginning of Ruby 1.9 support
FFI subsystem for calling C libraries[22]
1.2.0 2009-03-16 Ruby 1.9 support almost complete (including JIT compiler)
Preliminary Android support

Answer 1

A detailed overview of what is done and what is missing can be found on their wiki. From that page:

These are entire areas that need to be worked on.

• Encoding::Converter
• Yielder/Generator
• key Marshal changes
• cli options
• some RubyBignum changes
• possible other changes in Numerics
• changes in Dir/IO/File (some obvious things are done, like enumeratorize)
• some changes in Math
• encoding information in exception messages (now passed via java String)
• BigDecimal changes ?

In general, though, I think you’ll be fine if you use JRuby for Ruby 1.9 code. Any errors that you may have will be few and far between, and easily fixable (for the most part). I recommend you try your code with the latest JRuby, and if it doesn’t work, then you know not to use it yet.