Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
Enumerator::Lazy
Search
Erik Berlin
August 02, 2016
Programming
2
550
Enumerator::Lazy
Presented at SF.rb on August 2, 2016.
Erik Berlin
August 02, 2016
Tweet
Share
More Decks by Erik Berlin
See All by Erik Berlin
Ruby Trivia 3
sferik
0
690
The Value of Being Lazy
sferik
3
760
Ruby Trivia 2
sferik
0
730
Ruby Trivia
sferik
2
1.3k
💀 Symbols
sferik
5
1.9k
Content Negotiation for REST APIs
sferik
8
970
Writing Fast Ruby
sferik
628
61k
Mutation Testing with Mutant
sferik
5
1.1k
Other Decks in Programming
See All in Programming
2025-04-25 GitHub Copilot Agent ライブデモ(スクリプト)
goataka
0
120
読書シェア会 vol.4 『ダイナミックリチーミング 第2版』
kotaro666
0
120
Embracing Ruby magic
vinistock
2
270
音声プラットフォームのアーキテクチャ変遷から学ぶ、クラウドネイティブなバッチ処理 (20250422_CNDS2025_Batch_Architecture)
thousanda
0
430
カウシェで Four Keys の改善を試みた理由
ike002jp
1
140
データと事例で振り返るDevin導入の"リアル" / The Realities of Devin Reflected in Data and Case Studies
rkaga
3
2.6k
今話題のMCPサーバーをFastAPIでサッと作ってみた
yuukis
0
140
オープンソースコントリビュート入門
_katsuma
0
140
個人開発の学生アプリが企業譲渡されるまで
akidon0000
2
1.2k
監視 やばい
syossan27
12
10k
20250429 - CNTUG Meetup #67 / DevOps Taiwan Meetup #69 - Deep Dive into Tetragon: Building Runtime Security and Observability with eBPF
tico88612
0
190
私のRubyKaigi 2025 Kaigi Effect / My RubyKaigi 2025 Kaigi Effect
chobishiba
1
160
Featured
See All Featured
Build your cross-platform service in a week with App Engine
jlugia
231
18k
Making Projects Easy
brettharned
116
6.2k
Faster Mobile Websites
deanohume
307
31k
What's in a price? How to price your products and services
michaelherold
245
12k
Exploring the Power of Turbo Streams & Action Cable | RailsConf2023
kevinliebholz
32
5.8k
Evolution of real-time – Irina Nazarova, EuRuKo, 2024
irinanazarova
8
710
Principles of Awesome APIs and How to Build Them.
keavy
126
17k
The Myth of the Modular Monolith - Day 2 Keynote - Rails World 2024
eileencodes
24
2.7k
Building an army of robots
kneath
305
45k
Done Done
chrislema
184
16k
How to Ace a Technical Interview
jacobian
276
23k
Navigating Team Friction
lara
185
15k
Transcript
Enumerator::Lazy Erik Michaels-Ober @sferik
Imperative languages do iteration like this: int sum = 0;
for(i = 1; i < 10; i = i + 1) { sum = sum + i; }
Functional languages do iteration like this: rec_sum [] = 0
rec_sum (x:xs) = x + rec_sum xs rec_sum [1..9]
Object oriented languages (should) do iteration like this: sum =
0 (1..9).each do |i| sum += i end
Object oriented languages (should) do iteration like this: sum =
(1..9).inject(&:+)
Iterators Introduced in CLU by Barbara Liskov (1975) Copied in
Ruby by Yukihiro Matsumoto (1995)
Ruby’s iterator is called Enumerator
enum = Enumerator.new do |yielder| yielder.yield("sf") yielder.yield("dot") yielder.yield("rb") end
["sf", "dot", "rb"].each ["sf", "dot", "rb"].to_enum Enumerator.new(["sf", "dot", "rb"])
enum = Enumerator.new do |yielder| n = 0 loop do
yielder.yield(n) n += 1 end end
fib = Enumerator.new do |yielder| a = b = 1
loop do yielder.yield(a) a, b = b, a + b end end
module Enumerable def lazy_map(&block) Enumerator.new do |yielder| return to_enum(__method__) unless
block_given? each do |n| yielder.yield(block.call(n)) end end end end
module Enumerable def lazy_select(&block) Enumerator.new do |yielder| return to_enum(__method__) unless
block_given? each do |n| yielder.yield(n) if block.call(n) end end end end
Ruby 2.0 introduced Enumerator::Lazy
What are the first five even perfect squares over a
thousand?
lazy_integers = (1..Float::INFINITY).lazy lazy_integers.collect { |x| x ** 2 }.
select { |x| x.even? }. reject { |x| x < 1000 }. first(5) #=> [1024, 1156, 1296, 1444, 1600]
What are the first five twin primes?
require "prime" lazy_primes = Prime.lazy lazy_primes.select { |x| (x -
2).prime? }. collect { |x| [x - 2, x] }. first(5) #=> [[3, 5], [5, 7], [11, 13], [17, 19], [29, 31]]
module Enumerable def repeat_after_first return to_enum(__method__) unless block_given? each.with_index do
|*val, index| index.zero? ? yield(*val) : 2.times { yield(*val) } end end end
require "prime" lazy_primes = Prime.lazy lazy_primes.repeat_after_first. each_slice(2). select { |x,
y| x + 2 == y }. first(5) #=> [[3, 5], [5, 7], [11, 13], [17, 19], [29, 31]]
When are the next five Friday the 13ths?
require "date" lazy_dates = (Date.today..Date.new(9999)).lazy lazy_dates.select { |d| d.day ==
13 }. select { |d| d.friday? }. first(10)
Detect whether a text file contains a string? (without reading
the entire file into memory)
lazy_file = File.readlines("/path/to/file").lazy lazy_file.detect { |x| x =~ /regexp/ }
Being lazy is efficient.
Being lazy is elegant.
None
Thank you