This document discusses building the Ruby programming language in Smalltalk. It addresses some of the key challenges in doing so, including differences in the compilers, handling different argument arities between Ruby and Smalltalk methods, allowing Ruby and Smalltalk code to coexist, handling per-instance behavior, and tracking per-instance variables in Ruby. Synthetic "bridge" methods are discussed as one approach to addressing differences in argument arities. The document also shows how the number of core Ruby tests passed has increased over time, suggesting the choice to implement Ruby in Smalltalk was a good one.

1. Building Ruby
in
Smalltalk
Martin McClure
ESUG 2009

3. Why?

4. €

5. ...and more

6. GemStone
for
Really Smart
Dummies

7. GemStone/S
● Smalltalk Implementation
● Headless
● Shared transactional persistence
– Shared “image”
– Commit merges concurrent changes
– Large
●
Thousands of concurrent VMs
● Terabyte scale
– Fast
● 10K commits/sec

8. GemStone/S
It's
Just
Smalltalk

10. The Big Choice

11. Challenge 1:
The Compiler

12. Smalltalk Grammar

13. Ruby Grammar

14. Ruby 1.8.6 parse.y

15. Ruby 1.8.6 parse.y

16. Cheat

19. Challenge 2:
Arity

20. Arity Challenges
● Number of message send arguments and
method definition parameters may be
different.
●
'*' Argument and parameter – Array expansion
for variable arity
●
'&' block passing
●
Smalltalk VM expects sender and receiver arity
to always be fixed and to match

21. Cheat

22. Synthetic 'Bridge' Methods
● def foo(a,*b)
…
end
●
Compiles:
foo, foo*, foo&, foo*&,
foo:, foo:*, foo:&, foo:*&
foo::, foo::*, foo::&, foo::*&
foo:::, foo:::*, foo:::&, foo:::*&

23. Synthetic 'Bridge' Methods
● some_object.foo(a,b,*c)
compiles a send to selector foo::*
● Bridge method foo::* adapts number of
arguments and resends to actual foo variant

24. Challenge 3:
Coexistence
of Ruby and
Smalltalk

25. Immediate
Classes

26. Not
Cheat

27. Environment-specific behavior
● Method dictionary per class per environment
● Each send site specifies an environment
● Complicates full method lookup
●
Does not affect send-site caches

28. Challenge 4:
Per-instance
Behavior

29. Challenge 5:
Per-instance
Variables

30. In Ruby, an
instance variable
is created
by the act of
assigning to it.

31. Possible instvars are hard to find
class MyExample
def initialize(someValue)
@my_instvar = someValue
end
end
…
class MyExample
def setAlpha(newAlpha)
@alpha = newAlpha
end
end

32. Core Tests Passed Over Time

33. Did we
make the
right
choice?

34. Yes
We
Did

35. Cheat

36. Not
cheating
at all,
really

37. Thank
You
Questions?