Dissecting Ruby - Speaker Deck

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Dissecting a Ruby Block Pat Shaughnessy http://patshaughnessy.net BostonRB Sept. 11, 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 LFP

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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 LFP

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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

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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 computer science, a closure (also lexical closure or function closure) is a function or reference to a function together with a referencing environment...” Sussman and Steele. Scheme: An interpreter for extended lambda calculus

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Creating and calling a lambda

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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 LFP

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

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str rb_control_frame_t LFP rb_env_t env rb_proc_t rb_block_t iseq DFP envval is_lambda Stack Heap str

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display_message.call

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locals: str2 DFP rb_control_frame_t rb_env_t env rb_proc_t rb_block_t iseq DFP envval is_lambda Stack Heap str

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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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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 LFP self RObject ivptr klass @str etc...

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

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rb_control_frame_t LFP self rb_binding_t filename line_no env rb_env_t rb_block_t iseq DFP env self Stack Heap RObject ivptr klass @str etc...

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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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instance_eval

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

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str2 = "jumps over the lazy dog." obj = Quote.new obj.instance_eval do puts "#{@str} #{str2}" end

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instance_eval and singleton classes

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

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obj = Quote.new obj.instance_eval do def display_message puts @str end end

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obj.display_message The quick brown fox jumps over the lazy dog. Quote.new.display_message ...undefined method `display_message' for # (NoMethodError)

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RClass super RClass super Object (class) Kernel (module) Quote (class) RClass super RClass super BasicObject (class) RObject klass obj (object)

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etc... RClass super RClass super Object (class) obj (object) RObject klass SomeClass (class) RClass super #> (singleton)

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http://patshaughnessy.net/ruby-under-a-microscope