Dissecting a Ruby Block

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Dissecting a Ruby Block Pat Shaughnessy http://patshaughnessy.net @pat_shaughnessy RubyConf Nov. 1, 2012

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Why learn Ruby internals?

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10.times do |n| puts n end

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Blocks: Closures in Ruby Closures and Metaprogramming

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rb_block_t ??

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Calling a block

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10.times do str = "The quick brown fox..." puts str end

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rb_block_t iseq putstring "The quick brown fox… " setdynamic str, 0 putself getdynamic str, 0 send :puts, 1 leave

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Referencing variables from the parent scope

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str = "The quick brown fox" 10.times do str2 = "jumps over the lazy dog." puts "#{str} #{str2}" end

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str = "The quick brown fox"

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YARV internal stack locals: str rb_control_frame_t DFP Stack frame for top level scope

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str = "The quick brown fox" 10.times do ...

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YARV internal stack locals: str rb_block_t iseq DFP rb_control_frame_t DFP Stack frame for top level scope

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YARV internal stack locals: str rb_control_frame_t Stack frame for internal Fixnum.times C code

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... do str2 = "jumps over the lazy dog." puts "#{str} #{str2}" end

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rb_block_t iseq DFP YARV internal stack locals: str locals: str2 DFP rb_control_frame_t Stack frame for block code

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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, leave YARV internal stack locals: str

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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

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Creating and calling a lambda

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(lambda (arg) (/ arg 2))

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def display_message str = "The quick brown fox" lambda do str2 = "jumps over the lazy dog" puts "#{str} #{str2}" end end display_message.call

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def display_message str = "The quick brown fox" ... end

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YARV internal stack locals: str rb_control_frame_t Stack frame for message_function

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str = "The quick brown fox" lambda do ... end

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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

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display_message.call

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def display_message str = "The quick brown fox" lambda do str2 = "jumps over the lazy dog" puts "#{str} #{str2}" end end display_message.call

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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

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Blocks: Closures in Ruby Closures and Metaprogramming

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Using a closure to deﬁne a method

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class Quote def initialize @str = "The quick brown fox..." end def display_message puts @str end end

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class Quote def initialize @str = "The quick brown fox..." end define_method :display_message do puts @str end end

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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

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eval and binding

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str = "puts" str += " 2" str += " +" str += " 2" eval(str) => 4

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class Quote def initialize @str = "The quick brown fox..." end def get_binding binding end end

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obj = Quote.new

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rb_control_frame_t self DFP, LFP, SP YARV internal stack PC, etc. RObject ivptr klass @str etc...

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obj = Quote.new eval('puts @str', obj.get_binding)

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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

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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

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