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
Enumerators
Search
Oliver Legg
October 14, 2013
Programming
1
680
Enumerators
Oliver Legg
October 14, 2013
Tweet
Share
More Decks by Oliver Legg
See All by Oliver Legg
Ruby on Rails – A Primer
ollylegg
1
680
Presenters – Take II
ollylegg
1
460
Other Decks in Programming
See All in Programming
State of CSS 2025
benjaminkott
1
120
LLMOpsのパフォーマンスを支える技術と現場で実践した改善
po3rin
8
970
自作OSでDOOMを動かしてみた
zakki0925224
1
1.4k
【第4回】関東Kaggler会「Kaggleは執筆に役立つ」
mipypf
0
700
ワープロって実は計算機で
pepepper
2
1.4k
Flutterと Vibe Coding で個人開発!
hyshu
1
260
Constant integer division faster than compiler-generated code
herumi
2
690
オホーツクでコミュニティを立ち上げた理由―地方出身プログラマの挑戦 / TechRAMEN 2025 Conference
lemonade_37
2
490
実践!App Intents対応
yuukiw00w
1
340
Webinar: AI-Powered Development: Transformiere deinen Workflow mit Coding Tools und MCP Servern
danielsogl
0
160
実践 Dev Containers × Claude Code
touyu
1
240
CEDEC2025 長期運営ゲームをあと10年続けるための0から始める自動テスト ~4000項目を50%自動化し、月1→毎日実行にした3年間~
akatsukigames_tech
0
150
Featured
See All Featured
Designing for Performance
lara
610
69k
XXLCSS - How to scale CSS and keep your sanity
sugarenia
248
1.3M
How To Stay Up To Date on Web Technology
chriscoyier
790
250k
The Illustrated Children's Guide to Kubernetes
chrisshort
48
50k
How to Think Like a Performance Engineer
csswizardry
25
1.8k
Statistics for Hackers
jakevdp
799
220k
Why Our Code Smells
bkeepers
PRO
338
57k
Imperfection Machines: The Place of Print at Facebook
scottboms
268
13k
Let's Do A Bunch of Simple Stuff to Make Websites Faster
chriscoyier
507
140k
Building an army of robots
kneath
306
46k
What's in a price? How to price your products and services
michaelherold
246
12k
Side Projects
sachag
455
43k
Transcript
ENumerators
Enumerable #all? #any? #chunk #collect #collect_concat #count #cycle #detect #drop
#drop_while #each_cons #each_entry #each_slice #each_with_index #each_with_object #entries #find #find_all #find_index #first #flat_map #grep #group_by #include? #inject #lazy #map #max #max_by #min_by #minmax #minmax_by #none? #one? #partition #reduce #reject #reverse_each #select #slice_before #sort #sort_by #take #take_while #to_a #zip
Enumerator #each #feed #next #next_values #peek #peek_values #rewind #size #with_index
#with_object
enumerator = [1, 2, 3].each # => #<Enumerator: [1, 2,
3]:each> enumerator = [1, 2, 3].to_enum # => #<Enumerator: [1, 2, 3]:each> enumerator = [1, 2, 3].enum_for(:each) # => #<Enumerator: [1, 2, 3]:each>
def counter yield 1 yield 2 yield 3 end enumerator
= enum_for(:counter) enumerator.to_a # => [1, 2, 3]
with_object with_index
letters = ['a', 'a', 'a', 'b', 'b', 'c'] counts =
letters.inject({}) do |memo, letter| memo[letter] ||= 0 memo[letter] += 1 memo end # => {"a"=>3, "b"=>2, "c"=>1}
letters = ['a', 'a', 'a', 'b', 'b', 'c'] counts =
letters.each.with_object({}) do |letter, memo| memo[letter] ||= 0 memo[letter] += 1 end # => {"a"=>3, "b"=>2, "c"=>1}
range = (1..10) range.map.with_index {|n, i| n * i }
# => [0, 2, 6, 12, 20, 30, 42, 56, 72, 90] range.select.with_index {|_, i| i.even? } # => [1, 3, 5, 7, 9]
Iterator
enumerator = [1, 2, 3].each # => #<Enumerator: [1, 2,
3]:each> enumerator.next # => 1 enumerator.next # => 2 enumerator.next # => 3 enumerator.next # StopIteration: iteration reached an end
enumerator = [1, 2, 3].to_enum # => #<Enumerator: [1, 2,
3]:each> enumerator.peek # => 1 enumerator.peek # => 2 enumerator.peek # => 3 enumerator.next # => 1
loop do i = enumerator.next puts i # `loop` silently
rescues StopIteration end
Generator
fibonacci = Enumerator.new(Float::INFINITY) do |yielder| a, b = 0, 1
loop do yielder.yield a a, b = b, (a + b) end end
class SumOfNaturalNumbers < Enumerator def initialize super(Float::INFINITY) do |yielder| n
= 1 loop do yielder.yield (n * (n + 1)) / 2 n += 1 end end end end
def fibonacci a, b = 0, 1 loop do yield
a a, b = b, (a + b) end end enumerator = enum_for(:fibonacci) # => #<Enumerator: main:fibonacci>
LAZY
require 'prime' primes = Prime.instance primes .select {|i| i.to_s.end_with?('3') }
.take(10) # infinite loop
require 'prime' primes = Prime.instance primes .lazy .select {|i| i.to_s.end_with?('3')
} .take(10) .to_a # => [3, 13, 23, 43, 53, 73, 83, 103, 113, 163]
File.open('/usr/share/dict/words') .each_line .lazy .map(&:chomp) .take_while {|line| line.length < 10 }
.to_a
mine = ->(repository) { repository.owner == 'olly' } cutoff =
(Time.now - (365 * 24 * 60 * 60)).to_datetime year_old = ->(repository) { repository.commits.first.date > cutoff } client.repositories .lazy .select(&mine) .select(&year_old) .take(10) .each {|repository| puts repository.name }