Metaprogramming for Generalists

Talk given at EuRuKo 2018

Transcript: https://dejimata.com/2018/8/23/transcript-of-my-euruko-2018-talk
Video: https://www.youtube.com/watch?v=1fIlcnrJHxs&feature=youtu.be&t=225

Transcript

1. FOR GENERALISTS metaprogramming CHRIS SALZBERG
2. about me • My handle is @shioyama. • I live in Tokyo, Japan. • I’m a Canadian from Montréal. • I work at a company called Degica. • I’m the author of a gem called Mobility. • I blog at dejimata.com.
3. 1. generalist metaprogramming 2. building generic software
4. 1 generalist metaprogramming
5. metaprogramming
6. metaprogramming (noun)
7. metaprogramming (noun) 1. writing code that writes code
8. metaprogramming (noun) 1. writing code that writes code 2. technique in which computer programs have the ability to treat programs as their data
9. metaprogramming (noun) 1. writing code that writes code 2. technique in which computer programs have the ability to treat programs as their data 3. a way for a program to find out things about itself, or other programs
10. metaprogramming (noun) 1. writing code that writes code 2. technique in which computer programs have the ability to treat programs as their data 3. a way for a program to find out things about itself, or other programs 4. a bag of tricks
11. then
12. define_method Class.new class_eval instance_eval eval method_missing Module.new binding arity parameters method_added method send
13. (Normal) PROGRAMMING metaprogramming
15. ruby ruby
16. ruby ruby applications applications
17. ruby ruby applications applications libraries libraries
18. ruby ruby applications applications metaprogramming lives here libraries libraries
19. why?
20. generalization
21. generalization (noun) Formulation of general concepts from specific instances by abstracting common properties.
22. generalization (noun) Formulation of general concepts from specific instances by abstracting common properties.
23. generalization (noun) Formulation of general concepts from specific instances by abstracting common properties.
24. attribute
25. knockout experiment
26. class Model def initialize; @attributes = {}; end def self.define_attribute(name) define_method name do @attributes.fetch(name) end define_method "#{name}=" do |value| @attributes[name] = value end end end class Model def initialize; @attributes = {}; end def self.define_attribute(name) define_method name do @attributes.fetch(name) end define_method "#{name}=" do |value| @attributes[name] = value end end end control
27. class Talk < Model define_attribute :title define_attribute :abstract end talk = Talk.new talk.title = "Metaprogramming for Generalists" talk.title #=> "Metaprogramming for Generalists" talk.abstract = "It conjures up images of..." talk.abstract #=> "It conjures up images of..." control
28. class Talk < Model define_attribute :title define_attribute :abstract end talk = Talk.new talk.title = "Metaprogramming for Generalists" talk.title #=> "Metaprogramming for Generalists" talk.abstract = "It conjures up images of..." talk.abstract #=> "It conjures up images of..." abstraction is transparent control
29. class Model def initialize; @attributes = {}; end def get_attribute(name) @attributes.fetch(name) end def set_attribute(name, value) @attributes[name] = value end end class Model def initialize; @attributes = {}; end def get_attribute(name) @attributes.fetch(name) end def set_attribute(name, value) @attributes[name] = value end end knockout
30. class Talk < Model end talk = Talk.new talk.set_attribute(:title, "MP for Generalists") talk.get_attribute(:title) #=> "MP for Generalists" talk.set_attribute(:abstract, "It conjures...") talk.get_attribute(:abstract) #=> "It conjures..." knockout
31. class Talk < Model end talk = Talk.new talk.set_attribute(:title, "MP for Generalists") talk.get_attribute(:title) #=> "MP for Generalists" talk.set_attribute(:abstract, "It conjures...") talk.get_attribute(:abstract) #=> "It conjures..." abstraction is visible knockout
32. class Talk < Model end talk = Talk.new talk.set_attribute(:title, "MP for Generalists") talk.get_attribute(:title) #=> "MP for Generalists" talk.set_attribute(:abstract, "It conjures...") talk.get_attribute(:abstract) #=> "It conjures..." knockout names are arguments
33. application library control knockout
34. application library control knockout - abstraction invisible - send as message - speaks in language of domain - abstraction visible - send as argument - speaks in language of abstraction
35. application library control knockout - abstraction invisible - send as message - speaks in language of domain - abstraction visible - send as argument - speaks in language of abstraction - unknowns refer to code - hard to understand - unknowns do not refer to code - easier to understand
36. talk = Talk.find(...) first_name = talk.get_association(:speaker) .get_attribute(:first_name) comment = talk.get_association(:comments).build comment.set_attribute( :content, "#{first_name} is speaking")
37. would you use this?
38. talk = Talk.find(...) comment = talk.comments.build comment.content = "#{talk.speaker.first_name} is speaking")
39. metaprogramming levels the playing field by enabling libraries to translate unknowns into code
40. eval("foo")
41. eval("foo") foo
42. str = "..." eval("foo#{str}")
43. def fooval(str) eval("foo#{str}") end
44. attr_writer "foo"
45. attr_writer "foo" def foo=(value) @foo = value end
46. def define_writer(name) define_method("#{name}=") do |value| instance_variable_set(:"@#{name}", value) end end
47. def define_writer(name) attr_writer name end
48. control control contains metaprogramming method(s) knockout knockout
49. control control contains metaprogramming method(s) knockout knockout define_writer define_writer[2] [2] define_writer define_writer[1] [1] fooval fooval attr_writer "foo" attr_writer "foo" eval "foo" eval "foo"
50. control control contains metaprogramming method(s) knockout knockout define_writer define_writer[2] [2] define_writer define_writer[1] [1] fooval fooval attr_writer "foo" attr_writer "foo" not reducible to “normal” programming eval "foo" eval "foo"
51. begin module rescue def nil false class do case self @foo true end for while if else ensure until “normal programming” = cannot convert unknowns into code
52. (meta) PROGRAMMING “normal” programming
53. (meta) PROGRAMMING generic software
54. 2 building generic software
55. Jeremy Evans One of the best ways to write flexible software is to write generic software. Instead of designing a single API that completely handles a specific case, you write multiple APIs that handle smaller, more generic parts of that use case and then handling the entire case is just gluing those parts together.” “ “The Development of Sequel”, May 2012
56. equality
58. λ ~/dev/rails/ master ag "def ==[^\=]" -l
59. λ ~/dev/rails/ master ag "def ==[^\=]" -l activejob/test/cases/serializers_test.rb activejob/test/models/person.rb activemodel/lib/active_model/attribute_set.rb activemodel/lib/active_model/attribute_set/builder.rb activemodel/lib/active_model/attribute.rb activemodel/lib/active_model/type/value.rb activemodel/lib/active_model/type/binary.rb actionpack/lib/action_dispatch/middleware/stack.rb actionpack/lib/action_dispatch/http/mime_type.rb actionpack/lib/action_controller/metal/strong_parameters.rb actionview/lib/action_view/template/types.rb activesupport/lib/active_support/duration.rb activerecord/test/models/customer.rb activerecord/lib/active_record/associations/collection_proxy.rb activerecord/lib/active_record/relation.rb activerecord/lib/active_record/connection_adapters/sql_type_metadata.rb activerecord/lib/active_record/connection_adapters/mysql/type_metadata.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/range.rb activerecord/lib/active_record/connection_adapters/postgresql/type_metadata.rb activerecord/lib/active_record/connection_adapters/postgresql/utils.rb activerecord/lib/active_record/connection_adapters/column.rb activerecord/lib/active_record/core.rb activerecord/lib/active_record/relation/where_clause.rb activerecord/lib/active_record/reflection.rb activerecord/lib/active_record/association_relation.rb activerecord/lib/active_record/aggregations.rb
60. λ ~/dev/rails/ master ag "def ==[^\=]" -l activejob/test/cases/serializers_test.rb activejob/test/models/person.rb activemodel/lib/active_model/attribute_set.rb activemodel/lib/active_model/attribute_set/builder.rb activemodel/lib/active_model/attribute.rb activemodel/lib/active_model/type/value.rb activemodel/lib/active_model/type/binary.rb actionpack/lib/action_dispatch/middleware/stack.rb actionpack/lib/action_dispatch/http/mime_type.rb actionpack/lib/action_controller/metal/strong_parameters.rb actionview/lib/action_view/template/types.rb activesupport/lib/active_support/duration.rb activerecord/test/models/customer.rb activerecord/lib/active_record/associations/collection_proxy.rb activerecord/lib/active_record/relation.rb activerecord/lib/active_record/connection_adapters/sql_type_metadata.rb activerecord/lib/active_record/connection_adapters/mysql/type_metadata.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/range.rb activerecord/lib/active_record/connection_adapters/postgresql/type_metadata.rb activerecord/lib/active_record/connection_adapters/postgresql/utils.rb activerecord/lib/active_record/connection_adapters/column.rb activerecord/lib/active_record/core.rb activerecord/lib/active_record/relation/where_clause.rb activerecord/lib/active_record/reflection.rb activerecord/lib/active_record/association_relation.rb activerecord/lib/active_record/aggregations.rb
61. class Address attr_reader :street, :city, :country def initialize(street, city, country) @street, @city, @country = street, city, country end # ... def ==(other) other.is_a?(self.class) && other.street == street && other.city == city && other.country == country end end # activerecord/test/models/customer.rb:15
62. class GpsLocation attr_reader :gps_location # ... def latitude gps_location.split("x").first end def longitude gps_location.split("x").last end def ==(other) other.latitude == latitude && other.longitude == longitude end end # activerecord/test/models/customer.rb:45
63. class Address def ==(other) other.is_a?(self.class) && other.street == street && other.city == city && other.country == country end end class GpsLocation def ==(other) other.latitude == latitude && other.longitude == longitude end end
64. class Address def ==(other) other.street == street && other.city == city && other.country == country end end class GpsLocation def ==(other) other.latitude == latitude && other.longitude == longitude end end
65. class Address def ==(other) other.send(:street) == send(:street) && other.send(:city) == send(:city) && other.send(:country) == send(:country) end end class GpsLocation def ==(other) other.send(:latitude) == send(:latitude) && other.send(:longitude) == send(:longitude) end end
66. class Address def ==(other) [:street, :city, :country].all? { |key| other.send(key) == send(key) } end end other.send(:street) == send(:street) && other.send(:city) == send(:city) && other.send(:country) == send(:country)
67. class Address def ==(other) [:street, :city, :country].all? { |key| other.send(key) == send(key) } end end abstraction
68. class Address def ==(other) keys = [:street, :city, :country] keys.all? { |key| other.send(key) == send(key) } end end
69. class Address define_method :== do |other| keys = [:street, :city, :country] keys.all? { |key| other.send(key) == send(key) } end end
70. class Address keys = [:street, :city, :country] define_method :== do |other| keys.all? { |key| other.send(key) == send(key) } end end
71. class Address keys = [:street, :city, :country] define_method :== do |other| keys.all? { |key| other.send(key) == send(key) } end end method arguments
72. class Address keys = [:street, :city, :country] define_method :== do |other| keys.all? { |key| other.send(key) == send(key) } end end method body
73. class Address def self.equalize(*keys) define_method :== do |other| keys.all? { |key| other.send(key) == send(key) } end end equalize :street, :city, :country end
74. module Equalizer def equalize(*keys) define_method :== do |other| keys.all? { |key| other.send(key) == send(key) } end end end class Address extend Equalizer equalize :street, :city, :country end unknowns
75. require "equalizer" class Address extend Equalizer equalize :street, :city, :country end
76. generic softw Equalizer Address
77. class Address extend Equalizer equalize :street, :city, :country end class Address extend Equalizer equalize :street, :city, :country end class GpsLocation extend Equalizer equalize :latitude, :longitude end class GpsLocation extend Equalizer equalize :latitude, :longitude end require "equalizer" class AM::Type::Value extend Equalizer equalize :precision, :scale, :limit end class AM::Type::Value extend Equalizer equalize :precision, :scale, :limit end class AR::Attribute extend Equalizer equalize :name, :value_before_type_cast, :type end class AR::Attribute extend Equalizer equalize :name, :value_before_type_cast, :type end class AM::AttributeSet extend Equalizer equalize :attributes end class AM::AttributeSet extend Equalizer equalize :attributes end class AR::ConnectionAdapters::Column extend Equalizer equalize :attributes_for_hash end class AR::ConnectionAdapters::Column extend Equalizer equalize :attributes_for_hash end class AM::AttributeSet::Builder extend Equalizer equalize :materialize end class AM::AttributeSet::Builder extend Equalizer equalize :materialize end class AR::Relation::WhereClause extend Equalizer equalize :predicates end class AR::Relation::WhereClause extend Equalizer equalize :predicates end
78. module Equalizer def equalize(*keys) define_method :== do |other| keys.all? { |key| other.send(key) == send(key) } end end end
79. module Equalizer def equalize(*keys) define_method :== do |other|; ... ; end define_method :inspect do "#<#{self.class.name}#{keys.map { |key| " #{key}=#{send(key).inspect} " }.join}>" end end end build on abstraction euruko2018 = Address.new("Neubaugürtel 34-36", "Wein", "Austria") euruko2018.inspect #=> #<Address street="Neubaugürtel 34-36" city="Wien" address="Austria" > euruko2018 = Address.new("Neubaugürtel 34-36", "Wein", "Austria") euruko2018.inspect #=> #<Address street="Neubaugürtel 34-36" city="Wien" address="Austria" >
80. module Equalizer def equalize(*keys) define_method :== do |other|; ... ; end define_method :inspect do; ... ; end define_method :hash do keys.map({ |key| send(key) }).hash end end end point_a = GpsLocation.new(1, 2) point_b = GpsLocation.new(1, 2) visits = {} visits[point_a] = 1 visits[point_b] = 2 visits #=> { #<GpsLocation lat=1 long=2>=>2 } point_a = GpsLocation.new(1, 2) point_b = GpsLocation.new(1, 2) visits = {} visits[point_a] = 1 visits[point_b] = 2 visits #=> { #<GpsLocation lat=1 long=2>=>2 } build on abstraction
83. To be a generalist
84. To be a generalist generalist
85. To be a generalist generalist
86. To be a generalist generalists
87. Chris Salzberg @shioyama / dejimata.com
88. credits • Satellite image of Tokyo neighbourhood in self-intro used Google Maps • Visualization of dry-rb gems network created using Graph Commons (graphcommons.com) • Image of Ruby from: – http://pngimg.com/download/22155