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
Decimal、正しく使ってる? / Are you using Decimal correc...
Search
Elvis Shi
December 15, 2021
Programming
4
730
Decimal、正しく使ってる? / Are you using Decimal correctly?
Elvis Shi
December 15, 2021
Tweet
Share
More Decks by Elvis Shi
See All by Elvis Shi
個人アプリを2年ぶりにアプデしたから褒めて / I just updated my personal app, praise me!
lovee
0
370
How did I build an Open-Source SwiftUI Toast Library
lovee
1
76
SwiftUIで使いやすいToastの作り方 / How to build a Toast system which is easy to use in SwiftUI
lovee
3
840
SwiftUIで二重スクロール作ってみた / When I tried to make a dual-scroll-ish view in SwiftUI
lovee
1
290
Observation のあれこれ / A brief introduction about Observation
lovee
3
360
ChatGPT 時代の勉強 / Learning under ChatGPT era
lovee
27
8.7k
属人化しない為の勉強会作り / To make tech meetups with less personal dependencies
lovee
0
310
偏見と妄想で語るスクリプト言語としての Swift / Swift as a Scripting Language
lovee
2
840
danger-swift-kantoku
lovee
1
530
Other Decks in Programming
See All in Programming
SwiftUI移行のためのインプレッショントラッキング基盤の構築
kokihirokawa
0
220
Accelerate your key learnings of scaling modern Android apps
aldefy
0
190
Functional APIから再考するLangGraphを使う理由
os1ma
4
570
Your Architecture as a Crime Scene:Forensic Analysis @bastacon 2025 in Frankfurt
manfredsteyer
PRO
0
150
15分で学ぶDuckDBの可愛い使い方 DuckDBの最近の更新
notrogue
3
910
AIレビュー導入によるCIツールとの共存と最適化
kamo26sima
1
1.4k
The Price of Micro Frontends… and Your Alternatives @bastacon 2025 in Frankfurt
manfredsteyer
PRO
0
360
イベントソーシングによってインピーダンスミスマッチから解放された話
tkawae
1
130
보일러플레이트 코드가 진짜 나쁜 건가요?
gaeun5744
0
310
フロントエンドオブザーバビリティ on Google Cloud
yunosukey
0
140
エンジニアに許された特別な時間の終わり
watany
83
70k
PEPCは何を変えようとしていたのか
ken7253
3
340
Featured
See All Featured
No one is an island. Learnings from fostering a developers community.
thoeni
21
3.2k
Let's Do A Bunch of Simple Stuff to Make Websites Faster
chriscoyier
507
140k
Agile that works and the tools we love
rasmusluckow
328
21k
Being A Developer After 40
akosma
89
590k
The Myth of the Modular Monolith - Day 2 Keynote - Rails World 2024
eileencodes
22
2.5k
Large-scale JavaScript Application Architecture
addyosmani
511
110k
Distributed Sagas: A Protocol for Coordinating Microservices
caitiem20
330
21k
RailsConf & Balkan Ruby 2019: The Past, Present, and Future of Rails at GitHub
eileencodes
134
33k
How to Create Impact in a Changing Tech Landscape [PerfNow 2023]
tammyeverts
50
2.3k
Why You Should Never Use an ORM
jnunemaker
PRO
55
9.2k
Keith and Marios Guide to Fast Websites
keithpitt
411
22k
How To Stay Up To Date on Web Technology
chriscoyier
790
250k
Transcript
%FDJNBMɺਖ਼ͬͯ͘͠Δʁ forJ1IPOF%FW4BQQPSPGFBU)","5"TXJGU
} var employedBy = "YUMEMI Inc." var job = "iOS
Tech Lead" var favoriteLanguage = "Swift" var twitter = "@lovee" var qiita = "lovee" var github = "el-hoshino" var additionalInfo = """ M1 Max MacBook Proࠓಧ͍ͨʂ """ final class Me: Developable, Talkable {
ʲใʳΏΊΈɺ҉߸௨՟Λൃߦʂ ˞ӕͰ͢ɻ
ͱ͍͏Θ͚Ͱ ΏΊΈͷڅ༩:VNF$PJOͰࢧڅʹ ˞ӕͰ͢ɻ
// ࠓ݄ͷڅ༩ var myYumeCoin = 0.2 // ࠓ݄ͷϘʔφε myYumeCoin +=
0.1 // ϘʔφεΛͬͯങ͍ʂ myYumeCoin -= 0.1 // ߴ֬ೝ print(myYumeCoin) // 0.20000000000000004 ??????
ͳͥ͜Μͳ͜ͱ͕ى͜Δͷ͔ w 4XJGUͰখΛѻ͏ͱ͖ɺσϑΥϧτͰDouble͕ ΘΕΔ w Doubleʮഒਫ਼ුಈখʯͳͷͰɺਫ਼ͷ Ͱͦͦਖ਼֬ʹදͤͳ͍ࣈ͕ͨ͘͞Μ͋Δ w େͷ߹ͦͷؙΊΒΕͨࣈͰʹͳΒͳ͍ ͕ɺۚ༥ܥͳͲͷ߹ਖ਼֬ʹѻ͏ඞཁ͕͋Δ
Decimal
Decimalܕ w ුಈখΛेਐϕʔεͰѻ͏ͨΊͷܕ w ༗ޮܻ͕ܻ w ༗ޮܻൣғͰ͋Εेਐදهͷޡ͕ࠩͳ͍
// ࠓ݄ͷڅ༩ var myYumeCoin = 0.2 // ࠓ݄ͷϘʔφε myYumeCoin +=
0.1 // ϘʔφεΛͬͯങ͍ʂ myYumeCoin -= 0.1 // ߴ֬ೝ print(myYumeCoin) // 0.20000000000000004 ??????
import Foundation // ࠓ݄ͷڅ༩ var myYumeCoin: Decimal = 0.2 //
ࠓ݄ͷϘʔφε myYumeCoin += 0.1 // ϘʔφεΛͬͯങ͍ʂ myYumeCoin -= 0.1 // ߴ֬ೝ print(myYumeCoin) // 0.2 🎉 'PVOEBUJPO͕ඞཁ ܕΛ໌ࣔతʹ%FDJNBMʹࢦఆ
DecimalɺŜƃŤƄƃŬžŜŘŢŦ
DecimalɺŜƃŤƄƃŬžŜŘŢŦ ͱɺࢥͬͨʁ
import Foundation // ࠓ݄ͷڅ༩ var myYumeCoin: Decimal = 0.2 //
ࠓ݄ͷϘʔφε myYumeCoin += 0.1 // ϘʔφεΛͬͯങ͍ʂ myYumeCoin -= 0.1 // ߴ֬ೝ print(myYumeCoin) // 0.2 🎉
import Foundation // ࠓ݄ͷڅ༩ var myYumeCoin: Decimal = 0.2 //
ࠓ݄ͷϘʔφε myYumeCoin += 0.1 // ϘʔφεΛͬͯങ͍ʂ myYumeCoin -= 0.1 // Decimal Λͬͯਖ਼֬ͳڅ༩ܭࢉ͕Ͱ͖͔ͨΒ͍͑Ϙʔφεʂ myYumeCoin += 123.456 // ߴ֬ೝ print(myYumeCoin) // 123.65599999999997952 !!!?????
DecimalɺūŬŹƂŜŽūŘ
DecimalͷϦςϥϧೖ w খϦςϥϧͰDecimalΛೖͰ͖Δͷɺ ExpressibleByFloatLiteralΛར༻ͨ݁͠Ռ w ࣮init(floatLiteral value: Double) w DecimalΛ࡞ΔલʹͦͦઌʹҰճDoubleΛ
࡞ͬͯͦͷ݁ՌΛೖ͍ͯ͠Δ͚ͩʂ
খϦςϥϧͰ DecimalΛೖ͠ͳ͍Ͱʂ
%FDJNBMΛखܰʢʁʣʹѻ͏ͨΊͷ ΠχγϟϥΠβʔ • init(_ value: String, format: Decimal.FormatStyle, lenient:
Bool = true) throws // iOS 15+ • init?(string: String, locale: Locale? = nil) // iOS 7+ • // etc…
import Foundation // ࠓ݄ͷڅ༩ var myYumeCoin: Decimal = 0.2 //
ࠓ݄ͷϘʔφε myYumeCoin += 0.1 // ϘʔφεΛͬͯങ͍ʂ myYumeCoin -= 0.1 // Decimal Λͬͯਖ਼֬ͳڅ༩ܭࢉ͕Ͱ͖͔ͨΒ͍͑Ϙʔφεʂ myYumeCoin += 123.456 // ߴ֬ೝ print(myYumeCoin) // 123.65599999999997952 !!!?????
import Foundation // … // Decimal Λͬͯਖ਼֬ͳڅ༩ܭࢉ͕Ͱ͖͔ͨΒ͍͑Ϙʔφεʂ //myYumeCoin += 123.456
// ࠓͦ͜ʂ myYumeCoin += try! .init("123.456", format: .number) // ߴ֬ೝ print(myYumeCoin) // 123.656 🎉
DecimalɺͪΐͬͱͰ͖͔ͨͳ
ʲࢀߟʳ
IUUQTGPSVNTTXJGUPSHUIPXUPJOJUJBMJ[FEFDJNBM
IUUQTJEFBMSFBMJUZDPNQSPHSBNJOHTXJGUEFDJNBMTUSJOH
ʲએʳ
IUUQTZVNFNJDPOOQBTTDPNFWFOU
IUUQTXXXZVNFNJDPKQDBUFHPSZSFDSVJU