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
570
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
710
The Value of Being Lazy
sferik
3
790
Ruby Trivia 2
sferik
0
760
Ruby Trivia
sferik
2
1.3k
💀 Symbols
sferik
5
1.9k
Content Negotiation for REST APIs
sferik
8
1k
Writing Fast Ruby
sferik
628
62k
Mutation Testing with Mutant
sferik
5
1.1k
Other Decks in Programming
See All in Programming
The state patternの実践 個人開発で培ったpractice集
miyanokomiya
0
140
Claude Code と OpenAI o3 で メタデータ情報を作る
laket
0
130
tool ディレクティブを導入してみた感想
sgash708
1
150
Understanding Ruby Grammar Through Conflicts
yui_knk
1
120
Introduction to Git & GitHub
latte72
0
120
実践!App Intents対応
yuukiw00w
1
320
Langfuseと歩む生成AI活用推進
licux
3
290
CEDEC 2025 『ゲームにおけるリアルタイム通信への QUIC導入事例の紹介』
segadevtech
3
940
AHC051解法紹介
eijirou
0
610
新しいモバイルアプリ勉強会(仮)について
uetyo
1
260
Constant integer division faster than compiler-generated code
herumi
2
680
自作OSでDOOMを動かしてみた
zakki0925224
1
1.4k
Featured
See All Featured
Fashionably flexible responsive web design (full day workshop)
malarkey
407
66k
Visualization
eitanlees
146
16k
Mobile First: as difficult as doing things right
swwweet
223
9.9k
Agile that works and the tools we love
rasmusluckow
329
21k
The Myth of the Modular Monolith - Day 2 Keynote - Rails World 2024
eileencodes
26
3k
Product Roadmaps are Hard
iamctodd
PRO
54
11k
A better future with KSS
kneath
239
17k
The Power of CSS Pseudo Elements
geoffreycrofte
77
5.9k
Done Done
chrislema
185
16k
The Cost Of JavaScript in 2023
addyosmani
53
8.8k
We Have a Design System, Now What?
morganepeng
53
7.7k
A designer walks into a library…
pauljervisheath
207
24k
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