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.
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
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
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
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
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
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
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
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
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
application library control knockout - abstraction invisible - send as message - speaks in language of domain - abstraction visible - send as argument - speaks in language of abstraction
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
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
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
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
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
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
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
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
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
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
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
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
shioyama
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