method_missingの黒魔術っぷりについて

by Sho Nagata

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method_missingͷࠇຐज़ͬ΀Γʹ͍ͭͯ 2019/1/29 Ebisu.rb #21 גࣜձࣾΧΧΫίϜ ৯΂ϩάγεςϜຊ෦ ϚΠΫϩαʔϏεԽνʔϜ ௕ాɹᠳ

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Copyright © Kakaku.com Inc. All Rights Reserved. ࣗݾ঺հ ௕ాɹᠳʢͳ͕ͨɹ͠ΐ͏ʣ • మಓܥSIerͰSEΛ7೥൒ • 2018೥9݄ʹΧΧΫίϜೖࣾ • όοΫΤϯυΤϯδχΞͱͯ͠৯΂ϩάͷϚΠΫϩαʔϏε ԽΛਪਐத • Ruby / Railsྺ͸5ϲ݄ • ݸਓతʹMachine Learning΍Blockchain৮ͬͨΓ • ޷͖ͳݴޠ͸Python • Ϛϥιϯ΍ͬͨΓΪλʔ΍ͬͨΓғޟ΍ͬͨΓ • 2ࣇͷ෕ ˏs_naga03 Sho Nagata nagata03

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ࠇຐज़ɿmethod_missing

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ࠇຐज़ɿmethod_missing

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ࠇຐज़ɿmethod_missing

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ࠇຐज़ɿmethod_missing

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Copyright © Kakaku.com Inc. All Rights Reserved. method_missing • BasicObjectΫϥεʹఆٛ͞Ε͍ͯΔprivateͳΠϯελϯεϝιου BasicObject.private_instance_methods.grep(/^method/) => [:method_missing] • ݺͼग़͞Εͨϝιου͕ɺܧঝπϦʔΛḷͬͯ୳ࡧͨ݁͠ՌͲ͜ʹ ΋ఆٛ͞Ε͍ͯͳ͔ͬͨ৔߹ɺmethod_missing͕ݺͼग़͞Ε NoMethodErrorΛൃੜͤ͞Δ

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Copyright © Kakaku.com Inc. All Rights Reserved. method_missingͷΦʔόʔϥΠυ class Sample def method_missing(name) puts “͋ͳͨ͸ΰʔετϝιου #{name} ϝιουΛݺͼग़͠·ͨ͠” end end sample = Sample.new sample.ghost #=> ͋ͳͨ͸ΰʔετϝιου ghost ϝιουΛݺͼग़͠·ͨ͠

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method_missingͷࠇຐज़ͬ΀Γ

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Copyright © Kakaku.com Inc. All Rights Reserved. method_missingͷࠇຐज़ͬ΀Γ • ΰʔετϝιου͸respond_to?Ͱ͸falseͱͳΔ sample = Sample.new sample.ghost #=> ͋ͳͨ͸ΰʔετϝιου ghost ϝιουΛݺͼग़͠·ͨ͠ sample.respond_to?(:ghost) #=> false

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Copyright © Kakaku.com Inc. All Rights Reserved. method_missingͷΦʔόʔϥΠυ class DS def get_keyboard_info(computer_id); end end class Computer def initialize(id, data_source) @id = id @data_source = data_source end def method_missing(name) @data_source.send(“get_#{name}_info, @id end def respond_to_missing?(method, include_private = false) @data_source.respond_to?(“get_#{method}_info”) || super end end

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Copyright © Kakaku.com Inc. All Rights Reserved. method_missingͷࠇຐज़ͬ΀Γ class Roulette def method_missing(name, *args) person = name.to_s.capitalize 3.times do number = rand(10) + 1 puts “#{number}…” end “#{person} got a #{number}” end end

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Copyright © Kakaku.com Inc. All Rights Reserved. method_missingͷࠇຐज़ͬ΀Γ class Roulette def method_missing(name, *args) person = name.to_s.capitalize super unless %w[Bob Frank Bill].include? person number = 0 3.times do number = rand(10) + 1 puts “#{number}…” end “#{person} got a #{number}” end end

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Copyright © Kakaku.com Inc. All Rights Reserved. method_missingͷࠇຐज़ͬ΀Γ irb(main):002:0> cmp = Computer.new(@id, DS.new) (Object doesn't support #inspect) => irb(main):003:0> cmp.class NoMethodError (undefined method `class' for #)

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·ͱΊ

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Copyright © Kakaku.com Inc. All Rights Reserved. method_missingͷΦʔόʔϥΠυ • ఆٛ͞Ε͍ͯͳ͍ϝιουʢΰʔετϝιουʣΛݺͼग़ͤΔΑ͏ʹͳΔ • ΰʔετϝιουʹ͍ͭͯrespond_to?ͰtrueΛฦ͢Α͏ʹ͍ͨ͠ͳΒ respond_to_missing?ϝιουΛΦʔόʔϥΠυ͠Α͏ • super Λ๨Εͣʹ • طଘͷϝιουΛݺͼग़ͯ͠͠·͏ՄೳੑΛ๨Εͣʹ

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