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Clean & fast code with Enumerators DENIS DEFREYNE RUG::B DECEMBER 7TH, 2017

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1. Simple HTTP client

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{ "books": [ { "id": "B98312", "title": "The Monkey's Raincoat", "author": "Oswaldo Berge" }, { "id": "B98318", "title": "The World, the Flesh and the Devil", "author": "Haleigh Thompson" } ] }

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def fetch_books(base_url) url = base_url + '/books' response = NetUVHTTP.get_response(URI.parse(url)) case response.code when '200' body = JSON.parse(response.body) body.fetch('books') else raise "Unexpected response code: #{response.code}" end end

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books = fetch_books('http://localhost:4567') books.each do |book| p book end

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2. Paginating HTTP client

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{ "books": [ { "id": "B98312", "title": "The Monkey's Raincoat", "author": "Oswaldo Berge" }, { "id": "B98318", "title": "The World, the Flesh and the Devil", "author": "Haleigh Thompson" } ], "cursor": "B98318" }

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def fetch_books(base_url) url = base_url + '/books' response = NetUVHTTP.get_response(URI.parse(url)) case response.code when '200' body = JSON.parse(response.body) body.fetch('books') else raise "Unexpected response code: #{response.code}" end end

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def fetch_books(base_url) books = [] loop do url = base_url + '/books' response = NetUVHTTP.get_response(URI.parse(url)) case response.code when '200' body = JSON.parse(response.body) books.concat(body.fetch('books')) break else raise "Unexpected response code: #{response.code}" end end books end

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def fetch_books(base_url) books = [] cursor = nil loop do url = base_url + '/books' url += "?cursor=#{cursor}" if cursor response = NetUVHTTP.get_response(URI.parse(url)) case response.code when '200' body = JSON.parse(response.body) books.concat(body.fetch('books')) cursor = body.fetch('cursor') break if cursor.nil? else raise "Unexpected response code: #{response.code}" end end books end

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def fetch_books(base_url) books = [] cursor = nil loop do url = base_url + '/books' url += "?cursor=#{cursor}" if cursor response = NetUVHTTP.get_response(URI.parse(url)) case response.code when '200' body = JSON.parse(response.body) books.concat(body.fetch('books')) cursor = body.fetch('cursor') break if cursor.nil? else raise "Unexpected response code: #{response.code}" end end books end

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books = fetch_books('http://localhost:4567') books.each do |book| p book end

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3. Refactoring

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def fetch_books(base_url) books = [] cursor = nil loop do url = base_url + '/books' url += "?cursor=#{cursor}" if cursor response = NetUVHTTP.get_response(URI.parse(url)) case response.code when '200' body = JSON.parse(response.body) books.concat(body.fetch('books')) cursor = body.fetch('cursor') break if cursor.nil? else raise "Unexpected response code: #{response.code}" end end books end

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def fetch_books(base_url)
 cursor = nil loop do url = base_url + '/books' url += "?cursor=#{cursor}" if cursor response = NetUVHTTP.get_response(URI.parse(url)) case response.code when '200' body = JSON.parse(response.body) body.fetch('books').each { |b| yield(b) } cursor = body.fetch('cursor') break if cursor.nil? else raise "Unexpected response code: #{response.code}" end end
 
 end

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fetch_books('http://localhost:4567') do |book| p book end

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4. More refactoring

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def fetch_books(base_url) cursor = nil loop do url = base_url + '/books' url += "?cursor=#{cursor}" if cursor response = NetUVHTTP.get_response(URI.parse(url)) case response.code when '200' body = JSON.parse(response.body) body.fetch('books').each { |b| yield(b) } cursor = body.fetch('cursor') break if cursor.nil? else raise "Unexpected response code: #{response.code}" end end end

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def fetch(base_url) cursor = nil loop do url = base_url url += "?cursor=#{cursor}" if cursor response = NetUVHTTP.get_response(URI.parse(url)) case response.code when '200' body = JSON.parse(response.body) yield(body) cursor = body.fetch('cursor') break if cursor.nil? else raise "Unexpected response code: #{response.code}" end end end

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fetch('http://localhost:4567/books') do |response| response.fetch('books').each do |book| p book end end

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responses = [] fetch('http://localhost:4567/books') do |response| responses << response end books = responses.map { |r| r.fetch('books') }.flatten books.each do |book| p book end

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responses = [] fetch('http://localhost:4567/books') do |response| responses << response end
 
 
 
 
 


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responses = to_enum(gfetch, 'http://localhost:4567/books')
 
 
 
 
 
 
 
 


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responses = to_enum(gfetch, 'http://localhost:4567/books')
 responses.each do |response| p response end
 
 
 
 


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responses = to_enum(gfetch, 'http://localhost:4567/books') books = responses.flat_map { |r| r.fetch('books') } 
 
 
 


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(1..3).map { |i| [i, 10+i] } # h> [[1, 11], [2, 12], [3, 13]] 


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(1..3).map { |i| [i, 10+i] } # h> [[1, 11], [2, 12], [3, 13]] (1..3).flat_map { |i| [i, 10+i] } # h> [1, 11, 2, 12, 3, 13]

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responses = to_enum(gfetch, 'http://localhost:4567/books') books = responses.flat_map { |r| r.fetch('books') } books.each do |book| p book end
 
 
 


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def fetch(base_url) return to_enum(__method__, base_url).lazy unless block_given? … end

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books = fetch('http://localhost:4567/books') .flat_map { |r| r.fetch('books') }

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def fetch(base_url) return to_enum(__method__, base_url).lazy unless block_given? cursor = nil loop do url = base_url url += "?cursor=#{cursor}" if cursor response = NetUVHTTP.get_response(URI.parse(url)) case response.code when '200' body = JSON.parse(response.body) yield(body) cursor = body.fetch('cursor') break if cursor.nil? else raise "Unexpected response code: #{response.code}" end end end

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5. Database

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db = Database.connect books = fetch('http://localhost:4567/books') .flat_map { |r| r.fetch('books') }
 
 books.each_slice(50) { |batch| db.store(batch) }

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Given ‣ 200 books ‣ HTTP response contains 50 books ‣ it takes 1s to fetch a batch of books ‣ it takes 1s to store a batch of books


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Given ‣ 200 books ‣ HTTP response contains 50 books ‣ it takes 1s to fetch a batch of books ‣ it takes 1s to store a batch of books
 Question How long does this code take to execute?
 
 3s 4s 5s 8s 16s

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Given ‣ 200 books ‣ HTTP response contains 50 books ‣ it takes 1s to fetch a batch of books ‣ it takes 1s to store a batch of books
 Question How long does this code take to execute?
 
 3s 4s 5s 8s 16s

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Fetch Store Fetch Store

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Fetch Store Fetch Store

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6. Buffer

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gem 'slow_enumerator_tools'

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db = Database.connect books = fetch('http://localhost:4567/books') .flat_map { |r| r.fetch('books') }
 
 
 books.each_slice(50) { |batch| db.store(batch) }

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db = Database.connect books = fetch('http://localhost:4567/books') .flat_map { |r| r.fetch('books') }
 books = SlowEnumeratorTools.buffer(books, 50)
 
 books.each_slice(50) { |batch| db.store(batch) }

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Given ‣ 200 books ‣ HTTP response contains 50 books ‣ it takes 1s to fetch a batch of books ‣ it takes 1s to store a batch of books


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Given ‣ 200 books ‣ HTTP response contains 50 books ‣ it takes 1s to fetch a batch of books ‣ it takes 1s to store a batch of books
 Question How long does this code take to execute?
 
 3s 4s 5s 8s 16s

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Given ‣ 200 books ‣ HTTP response contains 50 books ‣ it takes 1s to fetch a batch of books ‣ it takes 1s to store a batch of books
 Question How long does this code take to execute?
 
 3s 4s 5s 8s 16s

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Fetch Store

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7. Batches

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db = Database.connect books = fetch('http://localhost:4567/books') .flat_map { |r| r.fetch('books') }
 books = SlowEnumeratorTools.buffer(books, 50)
 
 
 books.each_slice(50) { |batch| db.store(batch) }

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db = Database.connect books = fetch('http://localhost:4567/books') .flat_map { |r| r.fetch('books') }
 books = SlowEnumeratorTools.buffer(books, 50)
 book_batches = SlowEnumeratorTools.batch(books)
 
 book_batches.each { |batch| db.store(batch) }

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events = MyEventStream.new('content') events.each do |_e| system('./rebuild.sh') end

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events = MyEventStream.new('content') event_batches = SlowEnumeratorTools.batch(events) event_batches.each do |_es| system('./rebuild.sh') end

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9. Merging

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content_events = MyEventStream.new('content') layout_events = MyEventStream.new('layouts')

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content_events = MyEventStream.new('content') layout_events = MyEventStream.new('layouts') events = SlowEnumeratorTools.merge( [content_events, layout_events])

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content_events = MyEventStream.new('content') layout_events = MyEventStream.new('layouts') events = SlowEnumeratorTools.merge( [content_events, layout_events]) event_batches = SlowEnumeratorTools.batch(events) event_batches.each do |es| system('./rebuild.sh') end

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10. Everything together

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db = MyDB.new api_a = MyAPI.new(MyHTTPClient.new('example.com')) api_b = MyAPI.new(MyHTTPClient.new('example.org'))

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db = MyDB.new api_a = MyAPI.new(MyHTTPClient.new('example.com')) api_b = MyAPI.new(MyHTTPClient.new('example.org')) articles = SlowEnumeratorTools.merge( [api_a.articles, api_b.articles])

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db = MyDB.new api_a = MyAPI.new(MyHTTPClient.new('example.com')) api_b = MyAPI.new(MyHTTPClient.new('example.org')) articles = SlowEnumeratorTools.merge( [api_a.articles, api_b.articles]) articles = SlowEnumeratorTools.buffer(articles, 200)

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db = MyDB.new api_a = MyAPI.new(MyHTTPClient.new('example.com')) api_b = MyAPI.new(MyHTTPClient.new('example.org')) articles = SlowEnumeratorTools.merge( [api_a.articles, api_b.articles]) articles = SlowEnumeratorTools.buffer(articles, 200) article_batches = SlowEnumeratorTools.batch(articles)

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db = MyDB.new api_a = MyAPI.new(MyHTTPClient.new('example.com')) api_b = MyAPI.new(MyHTTPClient.new('example.org')) articles = SlowEnumeratorTools.merge( [api_a.articles, api_b.articles]) articles = SlowEnumeratorTools.buffer(articles, 200) article_batches = SlowEnumeratorTools.batch(articles) article_batches.each { |as| db.store_multi(as) }

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SlowEnumeratorTools.buffer(enum, size) SlowEnumeratorTools.batch(enum) SlowEnumeratorTools.merge(enums) github.com/ddfreyne/slow_enumerator_tools

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Now your code is clean & fast, thanks to Enumerators.

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DENIS DEFREYNE @DDFREYNE Q&A

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