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

About Me

Joshua BallancoName:

About Me

Ankara, TurkeyLocation:

About Me

Burnside DigitalEmployer:

How many Ruby implementations do

you use?

Matz’s Ruby InterpreterJRuby

Rubinius

IronRubyMacRuby

RubyMotion

MagLev Cardinal

Topaz

What impact do alternate Rubies have

on me?

What about fragmentation?

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!

What do you do when...

ArgumentError: comparison of ActiveSupport::TimeWithZone with ActiveSupport::TimeWithZone failed

A Side Note on Reading Code

Read Code

A Side Note on Reading Code

Read Code!

A Side Note on Reading Code

Read A Lot of Code

A Side Note on Reading Code

Read Twice as Much Code as You Write

A Side Note on Reading Code

Read Ten Times as Much Code as You Write

A Side Note on Reading Code

Read Code

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

Let’s Go Code Diving!

Confused yet?

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

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

We Have to go Deeper!

Read Code...and Comments

So Far...

• TimeWithZone initializes @utc to a Time or DateTime

• Comparison with <=> passes through “other” to @utc’s <=> operator

But then...

...why?

Remember This?

It Gets Worse...

Remember this?

Oh, ActiveSupport...

activesupport-3.2.13/lib/active_support/core_ext/date_time/calculations.rb

Oh, ActiveSupport...

activesupport-3.2.13/lib/active_support/core_ext/time/calculations.rb

This isn’t a Rails Talk...

Really...it’s not...

Getting to the Heart of the Matter: JRuby

• If “other” is a Time object, compare

• Otherwise: nil

src/org/jruby/RubyTime.java

Getting to the Heart of the Matter: MRI

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

So...Fix JRuby

1 Ruby Down1 To Go

AlwaysBeCurious

What Classes Reverse Compare Like This?• Time

• ...

• String

• ...

• That’s it!

BUT!

Oh, MRI...

Break it down...

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

Break it down...

If “other” can not be converted into a string, return nil

Break it down...

If “other” also doesn’t have its own comparison operator, return nil

Break it down...

If “other” does have its own comparison operator, call it and return the negation of the result

BUT! ...

Remember this?

Uhh...

Fun With Poorly Specified Behavior

...but I thought <=> only ever returned -1, 0, or 1?

So...Fix MRI

fin?Not quite...

What about...

Crap...

Fun With Mutual Recursion

Fun With Mutual Recursion

Fun With Mutual Recursion

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

finQuestions?