![class NilClass
# ...
def method_missing(method, *args, &block)
if klass = METHOD_CLASS_MAP[method]
raise_nil_warning_for klass, method, caller
else
super
end
end
end](https://image.slidesharecdn.com/therevengeofmethodmissinghr-110530041454-phpapp01/85/The-Revenge-of-method_missing-6-320.jpg)
The Revenge of method_missing()
- 1. The revenge of method_missing() Paolo “Nusco” Perrotta
- 2. Should I use method_missing() to remove duplication from my code, or should I avoid it like the plague? Paolo “Nusco” Perrotta
- 4. disclaimer
- 6. class NilClass # ... def method_missing(method, *args, &block) if klass = METHOD_CLASS_MAP[method] raise_nil_warning_for klass, method, caller else super end end end
- 8. class InfoDesk def flights # ... end def trains # ... end def hotels # ... end # ... end
- 9. class Sign def initialize @desk = InfoDesk.new end def flights return “Out for lunch” if Clock.lunch_time? @desk.flights end def trains return “Out for lunch” if Clock.lunch_time? @desk.local_transports end def hotels return “Out for lunch” if Clock.lunch_time? @desk.local_transports end # ... end
- 12. class Sign def initialize @desk = InfoDesk.new end def method_missing(name, *args) return “Out for lunch” if Clock.lunch_time? @desk.send(name, *args) end end # At 12:30... Sign.new.flights # => “Out for lunch”
- 13. Ghost Methods
- 14. class Sign def initialize @desk = InfoDesk.new end InfoDesk.public_instance_methods.each do |m| define_method(m) do return “Out for lunch” if Clock.lunch_time? @desk.send(m) end end end
- 15. Ghost Methods vs. Dynamic Methods
- 16. the four pitfalls of method_missing()
- 17. class Sign def initialize @desk = InfoDesk.new end def method_missing(name, *args) return “Out for lunch” if Clock.lunch_time? @desk.send(name, *args) end end
- 18. we have a problem
- 19. class Sign def initialize @desk = InfoDesk.new end def is_it_lunch_time_yet? Clock.lunch_time? end def method_missing(name, *args) return “Out for lunch” if is_it_lunchtime_yet? @desk.send(name, *args) end end # At 12:30... Sign.new.flights # => ?
- 20. class Sign def initialize @desk = InfoDesk.new end def is_it_lunch_time_yet? Clock.lunch_time? end def method_missing(name, *args) return “Out for lunch” if is_it_lunchtime_yet? @desk.send(name, *args) end end # At 12:30... Sign.new.flights # => ?
- 21. class Sign def initialize @desk = InfoDesk.new end def is_it_lunch_time_yet? Clock.lunch_time? end def method_missing(name, *args) return “Out for lunch” if is_it_lunchtime_yet? @desk.send(name, *args) end end # At 12:30... Sign.new.flights # => SystemStackError: stack level too deep
- 22. the first pitfall: the Ghost House
- 23. class Sign def initialize @desk = InfoDesk.new end def method_missing(name, *args) return super unless @desk.respond_to? name return “Out for lunch” if Clock.lunch_time? @desk.send(name, *args) end end
- 24. we have a problem
- 25. Sign.new.respond_to? :flights # => false
- 26. the second pitfall: the Liar Object
- 27. class Sign def initialize @desk = ::InfoDesk.new end def method_missing(name, *args) return super unless @desk.respond_to? name return “Out for lunch” if Clock.lunch_time? @desk.send(name, *args) end def respond_to?(method) @desk.respond_to?(method) || super end end Sign.new.respond_to? :flights # => true
- 28. we have a problem
- 29. class InfoDesk def flights # ... end def local_transports # ... end # ... def display # ... end end
- 30. Sign.new.display # => #<Sign:0x000001008451b0>
- 33. the third pitfall: the Fake Ghost
- 34. class Sign instance_methods.each do |m| undef_method m unless m.to_s =~ /^__|object_id/ end def initialize @desk = InfoDesk.new end def method_missing(name, *args) return super unless @desk.respond_to? name return "Out for lunch" if Clock.lunch_time? @desk.send(name, *args) end def respond_to?(method) @desk.respond_to? method || super end end Sign.new.display # => InfoDesk#display() called
- 35. class Sign < BasicObject def initialize @desk = ::InfoDesk.new end def method_missing(name, *args) return super unless @desk.respond_to? name return “Out for lunch” if ::Clock.lunch_time? @desk.send(name, *args) end def respond_to?(method) @desk.respond_to? method || super end end Sign.new.display # => InfoDesk#display() called
- 36. we have a problem (this is getting old already)
- 38. the fourth pitfall: the Snail Ghost
- 39. class Sign < BasicObject def initialize @desk = ::InfoDesk.new end def method_missing(name, *args) return super unless @desk.respond_to? name singleton_class.send :define_method, name do return “Out for lunch” if ::Clock.lunch_time? @desk.send name end send name end def respond_to?(method) @desk.respond_to? method || super end end # At 12:30... Sign.new.flights # => ?
- 40. class Sign < BasicObject def initialize @desk = ::InfoDesk.new end def method_missing(name, *args) return super unless @desk.respond_to? name singleton_class.send :define_method, name do return “Out for lunch” if ::Clock.lunch_time? @desk.send name end send name end def respond_to?(method) @desk.respond_to? method || super end end # At 12:30... Sign.new.flights # => SystemStackError: stack level too deep
- 41. class Sign < BasicObject def initialize @desk = ::InfoDesk.new end def method_missing(name, *args) return super unless @desk.respond_to? name singleton_class.send :define_method, name do return “Out for lunch” if ::Clock.lunch_time? @desk.send name end send name end def respond_to?(method) @desk.respond_to? method || super end end # At 12:30... Sign.new.flights # => SystemStackError: stack level too deep
- 44. should I use method_missing() to remove duplication in my code?
- 45. not if you can use define_method() instead
- 46. just a rule of thumb
- 47. remember the four pitfalls: the Ghost House the Liar Object the Fake Ghost the Snail Ghost
- 48. thank you.
Editor's Notes
- #2: aka...\n
- #3: I&#x2019;m assuming you know what m_m() is, but I&#x2019;m also going to show a basic example\n
- #4: - question at RubyKaigi\n- blog post on RubyLearning\n- disclaimer: this is about using method_missing() even when there are alternate techniques\n- there are cases where there is no alternative\n
- #5: \n
- #6: \n
- #7: (accessors, writing a DSL - think hard before you do this!)\nnot just for cutesy\n
- #8: example: whiny nils\n
- #9: \n
- #10: \n
- #11: \n
- #12: \n
- #13: \n
- #14: \n
- #15: ghost methods\n
- #16: \n
- #17: ghost methods\n
- #18: my own experiment\n
- #19: back to our original solution\nlet&#x2019;s do some refactoring\n
- #20: \n
- #21: \n
- #22: \n
- #23: \n
- #24: - any method you can call is a ghost\n - fix: always select the methods you're using\n\n\n
- #25: - fix: always remember to call super\n\n
- #26: \n
- #27: \n
- #28: no respond_to?\n(also, breaks the IDE and searches)\n\n
- #29: - fix: always implement respond_to?)\n- limitations of fix (methods(), etc)\n\n
- #30: \n
- #31: \n
- #32: \n
- #33: \n
- #34: \n
- #35: - fix: inherit from a Blank Slate\n\n
- #36: the &#x201C;scary&#x201D; solution\nwhich methods should I remove exactly?\n
- #37: \n
- #38: \n
- #39: \n
- #40: \n
- #41: - fix: (Reincarnation) lazily define methods with define_method() in method_missing()\n\n\n
- #42: ...but it doesn&#x2019;t work!\n
- #43: why it breaks\nwhat a mess! the experiment is over...\n
- #44: talking to jake scruggs\n
- #45: \n
- #46: \n
- #47: \n
- #48: \n
- #49: \n
- #50: \n
- #51: \n