Metaprogramming for Generalists

Transcript

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   FOR GENERALISTS metaprogramming CHRIS SALZBERG

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   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.
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   1. generalist metaprogramming 2. building generic software

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   1 generalist metaprogramming

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   metaprogramming

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   metaprogramming (noun)

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   metaprogramming (noun) 1. writing code that writes code

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   metaprogramming (noun) 1. writing code that writes code 2. technique

   in which computer programs have the ability to treat programs as their data
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   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
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    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
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    then

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    define_method Class.new class_eval instance_eval eval method_missing Module.new binding arity parameters

    method_added method send
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    (Normal) PROGRAMMING metaprogramming

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    None
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    ruby ruby

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    ruby ruby applications applications

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    ruby ruby applications applications libraries libraries

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    ruby ruby applications applications metaprogramming lives here libraries libraries

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    why?

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    generalization

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    generalization (noun) Formulation of general concepts from specific instances by

    abstracting common properties.
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    generalization (noun) Formulation of general concepts from specific instances by

    abstracting common properties.
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    generalization (noun) Formulation of general concepts from specific instances by

    abstracting common properties.
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    attribute

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    knockout experiment

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    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
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    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
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    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
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    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
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    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
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    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
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    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
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    application library control knockout

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    application library control knockout - abstraction invisible - send as

    message - speaks in language of domain - abstraction visible - send as argument - speaks in language of abstraction
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    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
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    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")
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    would you use this?

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    talk = Talk.find(...) comment = talk.comments.build comment.content = "#{talk.speaker.first_name} is

    speaking")
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    metaprogramming levels the playing field by enabling libraries to translate

    unknowns into code
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    eval("foo")

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    eval("foo") foo

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    str = "..." eval("foo#{str}")

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    def fooval(str) eval("foo#{str}") end

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    attr_writer "foo"

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    attr_writer "foo" def foo=(value) @foo = value end

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    def define_writer(name) define_method("#{name}=") do |value| instance_variable_set(:"@#{name}", value) end end

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    def define_writer(name) attr_writer name end

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    control control contains metaprogramming method(s) knockout knockout

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    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"
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    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"
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    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
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    (meta) PROGRAMMING “normal” programming

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    (meta) PROGRAMMING generic software

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    2 building generic software

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    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
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    equality

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    None
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    λ ~/dev/rails/ master ag "def ==[^\=]" -l

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    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
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    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
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    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
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    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
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    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
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    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
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    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
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    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)
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    class Address def ==(other) [:street, :city, :country].all? { |key| other.send(key)

    == send(key) } end end abstraction
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    class Address def ==(other) keys = [:street, :city, :country] keys.all?

    { |key| other.send(key) == send(key) } end end
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    class Address define_method :== do |other| keys = [:street, :city,

    :country] keys.all? { |key| other.send(key) == send(key) } end end
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    class Address keys = [:street, :city, :country] define_method :== do

    |other| keys.all? { |key| other.send(key) == send(key) } end end
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    class Address keys = [:street, :city, :country] define_method :== do

    |other| keys.all? { |key| other.send(key) == send(key) } end end method arguments
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    class Address keys = [:street, :city, :country] define_method :== do

    |other| keys.all? { |key| other.send(key) == send(key) } end end method body
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    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
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    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
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    require "equalizer" class Address extend Equalizer equalize :street, :city, :country

    end
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    generic softw Equalizer Address

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    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
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    module Equalizer def equalize(*keys) define_method :== do |other| keys.all? {

    |key| other.send(key) == send(key) } end end end
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    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" >
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    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
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    None
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    None
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    To be a generalist

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    To be a generalist generalist

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    To be a generalist generalist

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    To be a generalist generalists

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    Chris Salzberg @shioyama / dejimata.com

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    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