Code Quality Rank: L5
Programming language: Ruby
License: MIT License
Tags: Examples And Funny Stuff    
Latest version: v0.1.2

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Native Ruby extensions written in Crystal

Join the chat at https://gitter.im/phoffer/crystalized_ruby

Functional code for native extensions, without using FFI. This can utilize any Crystal code, i.e. existing shards.

This is still in heavy development and not ready for use. If you are interested in creating a proof of concept, I'm happy to assist. But otherwise, this isn't ready for real use.

Current work is splitting this repo into multiple repos:

  1. A Crystal shard that contains the Ruby bindings (will be this repo)
  2. A faster version of ActiveSupport::Inflector that utilizes inflector.cr as a native extension
  3. A Ruby gem that assists with generating a gem that uses Crystal for a native extension

This work is being done on the repo-split branch.

Class conversion status

Ruby class Ruby => Crystal Crystal => Ruby
String :white_check_mark: :white_check_mark:
Symbol :x: :white_check_mark:
Integer :white_check_mark:* :white_check_mark:
Float :x: :x:
Hash :x: :white_check_mark:
Array :white_check_mark: :white_check_mark:
Regexp :white_check_mark: :white_check_mark:
Nil :white_check_mark: :white_check_mark:
True :white_check_mark: :white_check_mark:
False :white_check_mark: :white_check_mark:


  • [ ] get all types working
    • [ ] float rb <=> cr
    • [ ] negative integers rb => cr
    • [ ] hash rb => cr
    • [ ] something for symbol rb => cr
  • [ ] be able to build gem and use (even just for checking type conversions)
  • [ ] separate repo into crystal shard for lib_ruby related, generator gem, and fast_inflector gem


See [updates.md](updates.md)


  • Negative integers don't convert correctly
  • Floats aren't working
  • I am having trouble with defining methods with various parameter counts. There's additional Crystal libs just for defining methods with zero or two parameters. This is obnoxious and the biggest annoyance I have right now, so I'd love to fix that soon.
  • I can't get a proc as a C callback working. There's some broken code commented out. Would love assistance from someone more knowledgeable. Right now this is for converting a Ruby hash to a Crystal hash.

How to get this working

Minimum crystal version: 0.16.0

Make sure Crystal is installed (Homebrew on OSX is fine)

Test and benchmark scripts both require fast_blank and active_support, mainly for comparison. Test script also uses descriptive_statistics, and the benchmark script uses benchmark-ips. None of these are required, except to run those two Ruby scripts. There's a Gemfile to install them if desired.

rake clean
rake compile
rake test


There is a benchmark script that compares a few things. The methods replicating ActiveSupport methods are copy-pasted, not even re-implemented from scratch. This uses the improved String#blank? method from AS 5.0, but it's not a hard requirement.

Some highlights (see results.txt for more):

        cr fibonacci:    22743.9 i/s
        rb fibonacci:      923.2 i/s - 24.63x slower

     empty string rb:  7591363.0 i/s
empty string crystal:  6973264.7 i/s - same-ish: difference falls within error

     CR blank string:  2393668.6 i/s
     AS blank string:   923967.3 i/s - 2.59x slower

           cr squish:   691693.1 i/s
           AS squish:   202554.1 i/s - 3.41x slower

          cr ordinal:  5044785.3 i/s
          AS ordinal:  1775271.7 i/s - 2.84x slower

       fast_blank rb:  6599201.8 i/s
       blank crystal:  2199386.4 i/s - 3.00x slower

Thanks and influences

There's three main projects that I've gained knowledge from to get this fully working:

These have all been incredibly helpful, and this is very closely modeled after the last two sources. @gaar4ica's also includes a PDF from a talk she gave at Fosdem, which was highly informative.

Future Ideas + Contributing

I'd like to get this more fully fleshed out, more functional, and get it usable. There is some question as to whether or not writing a native Ruby extension in Crystal is a useful idea, and I'd love to learn more about both why it would and would not be worthwhile, from people out there who are far more knowledgeable than I am.

If anyone is interested in this concept, please reach out to me either on this repo or on Twitter (@phoffer8). I'd love to collaborate with anyone interested, and just learn more in general.

Wish List

  • Complete the LibRuby wrapper for ruby.h and possibly a way to automate extracting the signatures from ruby.h into Crystal
  • Create a series of macros to create the wrappers of the Crystal methods (to convert input and output type between Crystal and CRuby)
  • Separate the LibRuby part into a separate gem/shard to make it reusable
  • If it was possible to create the aforementioned macros, then it would be great to create a generator to create the template of a Ruby gem with the native extension bits (libruby, extconf, makefile, etc)

Goal: to make it as easy as possible to create Ruby gems with Crystal-based native extensions where we could start with a "slow" Ruby source, tweak it quickly into a Crystal source file, wrap it up with LibRuby and compile it back as a native extension. No having to resort to C, Rust or other low level options.