Dissecting a Ruby Block

A deep dive into how MRI implements blocks, Ruby's implementation of closures. Also an explanation of the difference between blocks, lambdas, procs and bindings.

Transcript

1. Dissecting a Ruby Block Pat Shaughnessy http://patshaughnessy.net @pat_shaughnessy RubyConf Nov. 1, 2012
2. Why learn Ruby internals?
3. 10.times do |n| puts n end
5. Blocks: Closures in Ruby Closures and Metaprogramming
6. rb_block_t ??
7. Calling a block
8. 10.times do str = "The quick brown fox..." puts str end
9. rb_block_t iseq putstring "The quick brown fox… " setdynamic str, 0 putself getdynamic str, 0 send :puts, 1 leave
10. Referencing variables from the parent scope
11. str = "The quick brown fox" 10.times do str2 = "jumps over the lazy dog." puts "#{str} #{str2}" end
12. str = "The quick brown fox"
13. YARV internal stack locals: str rb_control_frame_t DFP Stack frame for top level scope
14. str = "The quick brown fox" 10.times do ...
15. YARV internal stack locals: str rb_block_t iseq DFP rb_control_frame_t DFP Stack frame for top level scope
16. YARV internal stack locals: str rb_control_frame_t Stack frame for internal Fixnum.times C code
17. ... do str2 = "jumps over the lazy dog." puts "#{str} #{str2}" end
18. rb_block_t iseq DFP YARV internal stack locals: str locals: str2 DFP rb_control_frame_t Stack frame for block code
19. rb_block_t iseq DFP putstring "jumps over the lazy dog." setdynamic str, 0 putself getdynamic str2, 1 tostring putstring " " getdynamic str, 0 tostring concatstrings 3 send :puts, 1, nil, 8, <ic:0> leave YARV internal stack locals: str
21. In order to solve this problem we introduce the notion of a closure [11, 14] which is a data structure containing a lambda expression, and an environment to be used when that lambda expression is applied to arguments. Sussman and Steele. Scheme: An interpreter for extended lambda calculus
22. Creating and calling a lambda
24. (lambda (arg) (/ arg 2))
25. def display_message str = "The quick brown fox" lambda do str2 = "jumps over the lazy dog" puts "#{str} #{str2}" end end display_message.call
26. def display_message str = "The quick brown fox" ... end
27. YARV internal stack locals: str rb_control_frame_t Stack frame for message_function
28. str = "The quick brown fox" lambda do ... end
29. YARV internal stack rb_env_t env rb_proc_t rb_block_t iseq DFP envval is_lambda Stack Heap str locals: str rb_control_frame_t message_function stack frame
30. display_message.call
31. def display_message str = "The quick brown fox" lambda do str2 = "jumps over the lazy dog" puts "#{str} #{str2}" end end display_message.call
32. YARV internal stack rb_control_frame_t stack frame for Proc.call Heap Stack str2 DFP rb_env_t env rb_proc_t rb_block_t iseq DFP envval is_lambda str
33. Blocks: Closures in Ruby Closures and Metaprogramming
34. Using a closure to define a method
35. class Quote def initialize @str = "The quick brown fox..." end def display_message puts @str end end
36. class Quote def initialize @str = "The quick brown fox..." end define_method :display_message do puts @str end end
37. class Quote def initialize @str = "The quick brown fox" end end str2 = "jumps over the lazy dog." Quote.send(:define_method, :display_message) do puts "#{@str} #{str2}" end
38. eval and binding
39. str = "puts" str += " 2" str += " +" str += " 2" eval(str) => 4
40. class Quote def initialize @str = "The quick brown fox..." end def get_binding binding end end
41. obj = Quote.new
42. rb_control_frame_t self DFP, LFP, SP YARV internal stack PC, etc. RObject ivptr klass @str etc...
43. obj = Quote.new eval('puts @str', obj.get_binding)
44. rb_binding_t line_no env Stack Heap rb_control_frame_t get_binding stack frame filename rb_env_t rb_block_t iseq DFP RObject ivptr klass @str self, DFP self
45. putstring "The quick brown fox… " setdynamic str, 0 putself getdynamic str, 0 send :puts, 1 leave YARV internal stack locals: str RObject ivptr klass rb_block_t DFP self iseq