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Decimal、正しく使ってる? / Are you using Decimal correctly?
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Elvis Shi
December 15, 2021
Programming
4
590
Decimal、正しく使ってる? / Are you using Decimal correctly?
Elvis Shi
December 15, 2021
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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