[spoiler]

It would be really cool if one could write binary extensions/gems for Ruby with Crystal somewhere down the line... far down the line, probably.

[asterite]

Yes, it's one of our dreams too. Right now you can do:

  # In a foo.cr file
  fun init_foo = Init_foo : Void
    puts "Init foo! :-)"
  end

Compiling it:

  bin/crystal foo.cr -o foo.bundle

Then in Ruby:

  $ irb
  irb(main):001:0> require "./foo"
  Init foo! :-)
  => true

But more complex things don't work right now (because of the initial implementation of the GC, which needs to be turned off for this case).

So, yes, we are not that far from allow you to write Ruby extensions in Crystal.

We'd also like to write Objective-C code that way, and also Erlang extensions.