The Future of Ruby

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Yukihiro Matsumoto's C implementation of Ruby aka Main Ruby Implementation is considered the Quasi-Standard of the Ruby Language since there has never been an explicit language standard for Ruby. As the number of implementations grows, however, a formal standard seems to become necessary to prevent the horror scenario of various non-conform interpreters.

The Danger of Diverging Implementations

None of the alternative implementations that are currently developed are yet complete and totally MRI conform. The stable MRI version is also continuously changed due to bug-fixing and improvements of the standard library. All alternative implementations are leaping behind the MRI and all the behavior changing fixes will have to be promoted to the alternative implementations in order to stay conform to MRI. Currently there is no explicit synchronization or standardization process to support this.

Microsoft has shown aggressive non-conformance policies in the past and is an old rival of Sun Microsystems. Both companies are developing alternative Ruby interpreters. It is possible that Ruby developers will be faced by the same problems as Java developer were, back then when Microsoft and Sun both provided mutually incompatible implementations of Java. In case Microsoft would again try to pull the same trick and release Iron Ruby for their .NET platform with intended incompatibilities -- possibly by taking performance optimizations as an excuse -- this would result in coding horrors for authors of pure Ruby applications and libraries which should run on both MRI and IronRuby. The greatest hope, however, is that Microsoft would probably not have any advantages from releasing IronRuby not conform to MRI because Ruby is not (yet) a market-dominating language. (Remark: IronRuby has been released to the open source community in Autumn 2007. At time of this writing, however, it was not yet clear what Microsoft would do with it.)

Nevertheless there is always the danger of diverging implementations. May it be for optimization's sake because Ruby code is hard to optimize due to its heavily dynamic nature or may it simply be due to the uncoordinated development processes of the different interpreters.

I hope, that the strong and vital Ruby community are aware of these and other problems the language will face in the near future all caused by missing standardization and synchronization activities.

Interpreter Standardization

There has been quite some effort to document the language's features in the form of books and online reference documentation. Almost all of the language's available documentation can be found on There are still many small holes in the documentation which is written by volunteers. Though these documentation resources are good enough for ruby developers they are not formal enough for the development of a ruby interpreter.

The JRuby folks have started a project called RubySpec which is a formal specification for the implementation of a Ruby interpreter. Later, the Rubinious crew and volunteers started to join in and formed it into a quite good language specification. This documents actually should be further developed and revised and declared as the official "Ruby Language Standard".

Another quite formal manifestation of the language's features are the unit tests of the MRI and other implementations. They should be united, revised and declared as the official "Standard Ruby Language Tests".

Such standardization tools would be a solid base for all different implementations of Ruby and unite their authors which could in the next step take part in the challenge for defining the future Ruby 2.0 standard.

Unifying the Ruby Standard Library

Currently every alternative distribution of Ruby is maintaining their own standard library. This obviously leads to various problems which also emerge from "copy-pasting" code in a program. Updates in the standard library will have to be merged into each implementation. Bugs will have to be fixed separately multiple times. Again, divergence of implementations is a result of all this. Applications depending on the standard library will have to check for the platform they are running resulting in undesirable code constructs like this:

when "JRuby"
    # fixes for JRuby
when "Ruby.NET"
    # fixes for .NET
when "IronRuby"
    # fixes for IronRuby
    # code for MRI or unknown platform

Such constructs will not be completely avoidably in some cases but they should really not have to be in user code. They should be implemented in a single instance of the standard library which should be factored out of MRI and transformed into an interpreter-independent standard library. Some of the standard library modules are native extensions which cannot be separated from their specific interpreter implementation but that should not keep us from unifying the pure ruby parts of the standard library.

Ruby Standardization Group

It cannot be denied that in the advent of multiple alternative Ruby implementations for different platforms there will be a great need for some explicit standardization activities and it is about time to do something. The first step could be to call for people who feel responsible for standardization (i.e. the authors of MRI and other implementations) and form a standardization group. Apparently the inventor of Ruby, Yukihiro Matsumoto, should be the head of this group. This seems to be the best way to coordinate and organize standardization activities.

List of Interpreters

Currently there are quite a lot different implementations of Ruby1.8 which are more or less complete. We will take a look at the most important and complete ones.

  • Ruby (MRI) The main implementation.
  • JRuby An almost complete implementation of the interpreter in Java.
  • Ruby.NET Still incomplete and unoptimized .NET compiler for Ruby.
  • Rubinious A not well known implementation based loosely on the Smalltalk-80 VM architecture.
  • Iron Ruby - Another implementation for .NET by Microsoft (has not yet been released).
  • YARV A virtual machine in C which has been merged into MRI 1.9. The YARV project itself is no longer maintained.

List of Unit Tests for the Ruby Language

  • JRuby's tests are at [1] in the test dir.
  • Rubinius's specs are at [2] in the spec dir.
  • RubyTests is at [3]