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
1
390
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
560
The Value of Being Lazy
sferik
3
590
Ruby Trivia 2
sferik
0
610
Ruby Trivia
sferik
2
1.1k
💀 Symbols
sferik
5
1.6k
Content Negotiation for REST APIs
sferik
8
820
Writing Fast Ruby
sferik
622
60k
Mutation Testing with Mutant
sferik
5
990
Other Decks in Programming
See All in Programming
Git Lint
bkuhlmann
4
760
dbtのドメイン分割による データ基盤の改善とDigdagとの連携
sakama
0
470
The Cutting Edge Of Versioning (LambdaConf 2024)
chriskrycho
0
180
GitHub Copilotのススメ
marcy731
1
240
Documentation for users with AsciiDoc and Antora
ahus1
0
370
新宿ダンジョンを可視化してみた
satoshi7190
3
410
効率化に挑戦してみたらモバイル開発が少し快適になった話
ryunakayama
0
140
Komplexe Oberflächen mit SVG und der Web Animation API
joergneumann
0
680
業務ツールとして使うPostman
msys75
0
110
障害対応を起点としたもっといい開発と運用のサイクル作りのためにできること / Hatena Enginner Seminar #29
polamjag
0
410
MetricKitで予期せぬ終了を検知する話 / Detect unexpected termination with MetricKit
nekowen
1
200
デフォルトにして至高、RubyMineの大好きな所
ruzia
0
980
Featured
See All Featured
"I'm Feeling Lucky" - Building Great Search Experiences for Today's Users (#IAC19)
danielanewman
221
21k
How STYLIGHT went responsive
nonsquared
92
4.8k
Being A Developer After 40
akosma
67
580k
Side Projects
sachag
451
41k
Java REST API Framework Comparison - PWX 2021
mraible
PRO
18
6.9k
Understanding Cognitive Biases in Performance Measurement
bluesmoon
12
1k
StorybookのUI Testing Handbookを読んだ
zakiyama
13
4.6k
Responsive Adventures: Dirty Tricks From The Dark Corners of Front-End
smashingmag
245
20k
Become a Pro
speakerdeck
PRO
13
4.6k
The Art of Programming - Codeland 2020
erikaheidi
43
12k
KATA
mclloyd
16
12k
What the flash - Photography Introduction
edds
64
11k
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