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Enumerator is an Enumerable Sergio Gil iamserg.io / @porras RUG::B July 2015

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Enumerator is an Enumerable Sergio Gil iamserg.io / @porras RUG::B July 2015 !

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Everyone ❤ Enumerable

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Everyone ❤ Enumerable FACT

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x.map { |i| i * i } # [1, 4, 9, 16, ...]

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x.map { |i| i * i } # [1, 4, 9, 16, ...] x.min # 1

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x.map { |i| i * i } # [1, 4, 9, 16, ...] x.min # 1 x.max # 9

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x.map { |i| i * i } # [1, 4, 9, 16, ...] x.min # 1 x.max # 9 x.all? { |i| i < 5 } # false

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x.map { |i| i * i } # [1, 4, 9, 16, ...] x.min # 1 x.max # 9 x.all? { |i| i < 5 } # false x.any?(&:odd?) # true

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x.map { |i| i * i } # [1, 4, 9, 16, ...] x.min # 1 x.max # 9 x.all? { |i| i < 5 } # false x.any?(&:odd?) # true x.detect { |i| i > 5 } # 6

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x.map { |i| i * i } # [1, 4, 9, 16, ...] x.min # 1 x.max # 9 x.all? { |i| i < 5 } # false x.any?(&:odd?) # true x.detect { |i| i > 5 } # 6 x.reduce(&:*) # 362880

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x.map { |i| i * i } # [1, 4, 9, 16, ...] x.min # 1 x.max # 9 x.all? { |i| i < 5 } # false x.any?(&:odd?) # true x.detect { |i| i > 5 } # 6 x.reduce(&:*) # 362880 x.select(&:odd?) # [1, 3, 5, 7, 9]

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x.map { |i| i * i } # [1, 4, 9, 16, ...] x.min # 1 x.max # 9 x.all? { |i| i < 5 } # false x.any?(&:odd?) # true x.detect { |i| i > 5 } # 6 x.reduce(&:*) # 362880 x.select(&:odd?) # [1, 3, 5, 7, 9] x.take_while { |i| i < 5 } # [1, 2, 3, 4]

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x.group_by { |i| i % 3 }
 # {0 => [3, 6, 9], 1 => [1, 4, 7], 2 => [2, 5, 8]}


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x.group_by { |i| i % 3 }
 # {0 => [3, 6, 9], 1 => [1, 4, 7], 2 => [2, 5, 8]}
 x.each_slice(3) { |slice| p slice }
 # [1, 2, 3]
 # [4, 5, 6]
 # [7, 8, 9]


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x.group_by { |i| i % 3 }
 # {0 => [3, 6, 9], 1 => [1, 4, 7], 2 => [2, 5, 8]}
 x.each_slice(3) { |slice| p slice }
 # [1, 2, 3]
 # [4, 5, 6]
 # [7, 8, 9]
 x.each_slice(3).map { |slice| slice.first }
 # [1, 4, 7]


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x.group_by { |i| i % 3 }
 # {0 => [3, 6, 9], 1 => [1, 4, 7], 2 => [2, 5, 8]}
 x.each_slice(3) { |slice| p slice }
 # [1, 2, 3]
 # [4, 5, 6]
 # [7, 8, 9]
 x.each_slice(3).map { |slice| slice.first }
 # [1, 4, 7]
 x.partition(&:odd?)
 # [[1, 3, 5, 7, 9], [2, 4, 6, 8]]

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http://www.rubydoc.info/stdlib/core/Enumerable

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x.map { |i| i * i } # [1, 4, 9, 16, ...] x.min # 1 x.max # 9 x.all? { |i| i < 5 } # false x.any?(&:odd?) # true x.detect { |i| i > 5 } # 6 x.reduce(&:*) # 362880 x.select(&:odd?) # [1, 3, 5, 7, 9] x.take_while { |i| i < 5 } # [1, 2, 3, 4]

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But what’s x?

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No content

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No t necessarily .

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http://www.rubydoc.info/stdlib/core/Enumerable

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And what’s an Enumerable?

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No content

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x = (1..9)

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My own Enumerable!

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1. Implement #each

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1. Implement #each 2. include Enumerable

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1. Implement #each 2. include Enumerable 3. No step 3

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three = [1, 2, 3] three.each { |i| puts i } three.map { |i| i * i } three.select(&:odd?) three.max three.first three.reduce(&:+)

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class Three include Enumerable def each yield 1 yield 2 yield 3 end end three = Three.new three.each { |i| puts i } three.map { |i| i * i } three.select(&:odd?) three.max three.first three.reduce(&:+)

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Recap so far:

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Recap so far: Enumerable is cool.

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Recap so far: Enumerable is cool. You can have your own Enumerables; just implement #each.

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Enumerator: an easy way to implement #each

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Also, no need to include Enumerable

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Fact 1. It takes a block which is not called but stored

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Fact 1. It takes a block which is not called but stored my_enum = Enumerator.new { raise '' } # nothing happens

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Fact 2. It implements #each, includes Enumerable

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Fact 2. It implements #each, includes Enumerable my_enum.respond_to?(:each) # true

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Fact 2. It implements #each, includes Enumerable my_enum.respond_to?(:each) # true my_enum.is_a?(Enumerable) # true

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And what does #each do?

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Well, it calls the block (that’s fact 3)

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Well, it calls the block (that’s fact 3) my_enum.each {} # example.rb:6:in `block in ': (RuntimeError) # from examples/facts.rb:16:in `each' # from examples/facts.rb:16:in `each' # from examples/facts.rb:16:in `'

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my_enum = Enumerator.new do |e| e << 'hello!' end my_enum.each do |item| p item end # "hello!"

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my_enum = [].tap do |a| a << 'hello!' end my_enum.each do |item| p item end # "hello!"

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No content

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No content

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Bonus Track: Enumerator::Lazy

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Bonus Track: Enumerator::Lazy my_enum.map(&:upcase).class # Array

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Bonus Track: Enumerator::Lazy my_enum.map(&:upcase).class # Array my_enum.lazy.map(&:upcase).class # Enumerator::Lazy

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Chaining! Even on infinite streams! Fibonacci.numbers.select { |i| i % 5 == 0 }. take_while { |i| i < 10 ** 6 }

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Chaining! Even on infinite streams! Fibonacci.numbers.select { |i| i % 5 == 0 }. take_while { |i| i < 10 ** 6 } # [0, 5, 55, 610, 6765, 75025, 832040]

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No content

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No content

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class Clock def self.seconds Enumerator.new do |e| loop do e << Time.now.to_i sleep 1 end end.lazy end end

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class Clock def self.seconds Enumerator.new do |e| loop do e << Time.now.to_i sleep 1 end end.lazy end end Clock.seconds.select(&:odd?).take(5).each do |time| p time end

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class Clock def self.seconds Enumerator.new do |e| loop do e << Time.now.to_i sleep 1 end end.lazy end end Clock.seconds.select(&:odd?).take(5).each do |time| p time end # 1435648191 # 1435648193 # 1435648195 # 1435648197 # 1435648199

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class Clock ... def self.minutes seconds.select { |t| t % 60 == 0 } end end

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No content

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CLOUDSOUND

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{ "tracks": [ { "id": 1, "duration": 37, "title": "Tools", "artist": "Tess Goyette Jr." }, ..., { "id": 11, "duration": 153, "title": "Grocery", "artist": "Geovanni McKenzie" } ], "meta": { "next": "http://localhost:4567/tracks?after=11" } } GET /tracks

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{ "tracks": [ { "id": 12, "duration": 153, "title": "Jewelery", "artist": "Berniece Hayes" }, ... { "id": 21, "duration": 161, "title": "Grocery & Beauty", "artist": "Adah Kozey" } ], "meta": { "next": "http://localhost:4567/tracks?after=21" } } GET /tracks?after=11

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class Api def initialize(url) @url = url end def tracks url = "#{@url}/tracks" Enumerator.new do |e| loop do data = get(url) data['tracks'].each do |track| e << track end url = data['meta']['next'] end end.lazy end end

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> api = Api.new('http://localhost:4567') =>

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> api = Api.new('http://localhost:4567') => > api.tracks => :each>>

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> api = Api.new('http://localhost:4567') => > api.tracks => :each>> > api.tracks.first => {"id"=>1, "duration"=>37, "title"=>"Tools", "artist"=>"Tess Goyette Jr."}

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> api = Api.new('http://localhost:4567') => > api.tracks => :each>> > api.tracks.first => {"id"=>1, "duration"=>37, "title"=>"Tools", "artist"=>"Tess Goyette Jr."} > api.tracks.drop(15).first => {"id"=>16, "duration"=>192, "title"=>"Clothing & Books", "artist"=>"Vicente Dickens"}

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> api = Api.new('http://localhost:4567') => > api.tracks => :each>> > api.tracks.first => {"id"=>1, "duration"=>37, "title"=>"Tools", "artist"=>"Tess Goyette Jr."} > api.tracks.drop(15).first => {"id"=>16, "duration"=>192, "title"=>"Clothing & Books", "artist"=>"Vicente Dickens"} > api.tracks.detect { |t| t['duration'] == 180 } => {"id"=>157, "duration"=>180, "title"=>"Health & Games", "artist"=>"Kareem Tillman DDS"}

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> total_duration = 0 => 0

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> total_duration = 0 => 0

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> total_duration = 0 => 0 > api.tracks.select { |track| track['duration'] > 120 }.take_while { |track| (total_duration += track['duration']) < 90 * 60 }.to_a

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> total_duration = 0 => 0 > api.tracks.select { |track| track['duration'] > 120 }.take_while { |track| (total_duration += track['duration']) < 90 * 60 }.to_a

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> total_duration = 0 => 0 > api.tracks.select { |track| track['duration'] > 120 }.take_while { |track| (total_duration += track['duration']) < 90 * 60 }.to_a => [{"id"=>2, "duration"=>144, "title"=>"Toys & Garden", "artist"=>"Rossie Senger"}, {"id"=>4, "duration"=>234, "title"=>"Baby", "artist"=>"Scottie Kling"}, {"id"=>5, "duration"=>215, "title"=>"Jewelery & Books", "artist"=>"Marge Simonis"}, {"id"=>7, "duration"=>216, "title"=>"Outdoors & Clothing", "artist"=>"Cortez Windler"}, {"id"=>11, "duration"=>153, "title"=>"Grocery", "artist"=>"Geovanni McKenzie"}, {"id"=>11, "duration"=>153, "title"=>"Jewelery", "artist"=>"Berniece Hayes"}, {"id"=>13, "duration"=>132, "title"=>"Toys, Movies & Health", "artist"=>"Joel Kuhlman"}, {"id"=>14, "duration"=>212, "title"=>"Jewelery & Games", "artist"=>"Jalyn Langosh"}, {"id"=>15, "duration"=>192, "title"=>"Clothing & Books", "artist"=>"Vicente Dickens"}, {"id"=>17, "duration"=>223, "title"=>"Industrial & Garden", "artist"=>"Archibald

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> total_duration = 0 => 0 > api.tracks.select { |track| track['duration'] > 120 }.take_while { |track| (total_duration += track['duration']) < 90 * 60 }.to_a => [{"id"=>2, "duration"=>144, "title"=>"Toys & Garden", "artist"=>"Rossie Senger"}, {"id"=>4, "duration"=>234, "title"=>"Baby", "artist"=>"Scottie Kling"}, {"id"=>5, "duration"=>215, "title"=>"Jewelery & Books", "artist"=>"Marge Simonis"}, {"id"=>7, "duration"=>216, "title"=>"Outdoors & Clothing", "artist"=>"Cortez Windler"}, {"id"=>11, "duration"=>153, "title"=>"Grocery", "artist"=>"Geovanni McKenzie"}, {"id"=>11, "duration"=>153, "title"=>"Jewelery", "artist"=>"Berniece Hayes"}, {"id"=>13, "duration"=>132, "title"=>"Toys, Movies & Health", "artist"=>"Joel Kuhlman"}, {"id"=>14, "duration"=>212, "title"=>"Jewelery & Games", "artist"=>"Jalyn Langosh"}, {"id"=>15, "duration"=>192, "title"=>"Clothing & Books", "artist"=>"Vicente Dickens"}, {"id"=>17, "duration"=>223, "title"=>"Industrial & Garden", "artist"=>"Archibald

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$ ruby examples/mixtape/mixtape.rb 45

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$ ruby examples/mixtape/mixtape.rb 45 14 tracks (44:17) Rossie Senger - Toys & Garden (2:24) Scottie Kling - Baby (3:54) Marge Simonis - Jewelery & Books (3:35) Cortez Windler - Outdoors & Clothing (3:36) Geovanni McKenzie - Grocery (2:33) Berniece Hayes - Jewelery (2:33) Joel Kuhlman - Toys, Movies & Health (2:12) Jalyn Langosh - Jewelery & Games (3:32) Vicente Dickens - Clothing & Books (3:12) Archibald Huels - Industrial & Garden (3:43) Adah Kozey - Grocery & Beauty (2:41) Mr. Geo Torp - Electronics (3:21) Doug Lesch - Jewelery, Health & Tools (3:08) Esta Daugherty - Shoes & Baby (3:53)

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Recap:

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Recap: Enumerable: do magic with lists.

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Recap: Enumerable: do magic with lists. Enumerator: do lists with everything.

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Thanks! Sergio Gil iamserg.io / @porras RUG::B July 2015 https://github.com/porras/enumerator-talk

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Thanks! Sergio Gil iamserg.io / @porras RUG::B July 2015 https://github.com/porras/enumerator-talk

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Thanks! Questions? Sergio Gil iamserg.io / @porras RUG::B July 2015 https://github.com/porras/enumerator-talk

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This talk’s little dirty secret

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Like on a koan,

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when the student finally understands Enumerator

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they’ll notice that

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they don’t need Enumerator

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there is no Enumerator

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Enumerator is #each

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Enumerator is #each #each is Enumerator

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class Api def initialize(url) @url = url end def tracks url = "#{@url}/tracks" Enumerator.new do |e| loop do data = get(url) data['tracks'].each do |track| e << track end url = data['meta']['next'] end end.lazy end end

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class Api def initialize(url) @url = url end def tracks Tracks.new("#{@url}/tracks").lazy end class Tracks def initialize(url) @url = url end def each url = @url loop do data = get(url) data['tracks'].each do |track| yield track end url = data['meta']['next'] end end include Enumerable end end https://github.com/porras/enumerator-talk/tree/no-enumerator

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and the student will be enlightened