Slides from the talk "A Tale of Two Rubies" that I presented at the RuLu 2013 conference.

1. A Tale of Two Rubies
...with apologies to Charles Dickens

2. About Me
Joshua BallancoName:

3. About Me
Ankara,TurkeyLocation:

4. About Me
Burnside DigitalEmployer:

5. How many Ruby
implementations do
you use?

6. Matz’s Ruby Interpreter
JRuby
Rubinius
IronRuby
MacRuby
RubyMotion
MagLev Cardinal
Topaz

7. What impact do
alternate Rubies have
on me?

8. What about
fragmentation?

9. A Story...
Once upon a time there was a Rails app,
that needed to be ported to JRuby
• Ditch C-extensions
• Look for JRuby specific versions of gems
• Find a good app server
• Run your test suite!

10. What do you do
when...
ArgumentError: comparison of ActiveSupport::TimeWithZone
with ActiveSupport::TimeWithZone failed

11. A Side Note on
Reading Code
Read Code

12. A Side Note on
Reading Code
Read Code!

13. A Side Note on
Reading Code
Read A Lot of Code

14. A Side Note on
Reading Code
Read Twice as Much
Code asYou Write

15. A Side Note on
Reading Code
Read Ten Times as Much
Code asYou Write

16. A Side Note on
Reading Code
Read Code

17. Let’s Go Code Diving!
activesupport-3.2.13/lib/active_support/time_with_zone.rb

18. Let’s Go Code Diving!

19. Confused yet?
When was the last time you called
TimeWithZone.new anyway???

20. We Have to go
Deeper!
activesupport-3.2.13/lib/active_support/core_ext/time/zones.rb
activesupport-3.2.13/lib/active_support/core_ext/date_time/zones.rb

21. We Have to go
Deeper!
Read Code
...and Comments

22. So Far...
• TimeWithZone initializes @utc to a Time
or DateTime
• Comparison with <=> passes through
“other” to @utc’s <=> operator

23. But then...
...why?

24. Remember This?

25. It Gets Worse...

26. Remember this?

27. Oh,ActiveSupport...
activesupport-3.2.13/lib/active_support/core_ext/date_time/calculations.rb

28. Oh,ActiveSupport...
activesupport-3.2.13/lib/active_support/core_ext/time/calculations.rb

29. This isn’t a Rails Talk...
Really...it’s not...

30. Getting to the Heart of
the Matter: JRuby
• If “other” is a Time object, compare
• Otherwise: nil
src/org/jruby/RubyTime.java

31. Getting to the Heart of
the Matter: MRI

32. Getting to the Heart of
the Matter: MRI
• If “other” is a Time object, compare
• If not, call <=> on other, passing self as the
argument
• If that works, take the negation of the
result
• Otherwise: nil

33. So...Fix JRuby

34. 1 Ruby Down
1 To Go

35. Always
Be
Curious

36. What Classes Reverse
Compare Like This?
• Time
• ...
• String
• ...
• That’s it!
BUT!

37. Oh, MRI...

38. Break it down...
If “other” is a string, do a string comparison
(in the else clause...yay)

39. Break it down...
If “other” can not be converted
into a string, return nil

40. Break it down...
If “other” also doesn’t have its own
comparison operator, return nil

41. Break it down...
If “other” does have its own
comparison operator, call it and
return the negation of the result
BUT! ...

42. Remember this?
Uhh...

43. Fun With Poorly
Specified Behavior
...but I thought <=> only ever
returned -1, 0, or 1?

44. So...Fix MRI

45. fin?
Not quite...

46. What about...
Crap...

47. Fun With Mutual
Recursion

48. Fun With Mutual
Recursion

49. Fun With Mutual
Recursion

50. The Moral
• When MRI was the only game in town,
whatever MRI did was “Ruby”
• Re-implementing “Ruby” allows us to
reconsider behaviors
• The key is communication and community

51. fin
Questions?