Decimal、正しく使ってる？ / Are you using Decimal correctly?

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%FDJNBMɺਖ਼͘͠࢖ͬͯΔʁ forJ1IPOF%FW4BQQPSPGFBU)","5"TXJGU

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} 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 Proࠓ೔ಧ͍ͨʂ """ final class Me: Developable, Talkable {

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ʲ଎ใʳΏΊΈɺ҉߸௨՟Λൃߦʂ ˞ӕͰ͢ɻ

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ͱ͍͏Θ͚Ͱ   ΏΊΈͷڅ༩͸:VNF$PJOͰࢧڅʹ ˞ӕͰ͢ɻ

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// ࠓ݄ͷڅ༩ var myYumeCoin = 0.2 // ࠓ݄ͷϘʔφε myYumeCoin += 0.1 // ϘʔφεΛ࢖ͬͯങ͍෺ʂ myYumeCoin -= 0.1 // ࢒ߴ֬ೝ print(myYumeCoin) // 0.20000000000000004 ??????

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ͳͥ͜Μͳ͜ͱ͕ى͜Δͷ͔ w 4XJGUͰখ਺Λѻ͏ͱ͖ɺσϑΥϧτͰ͸Double͕ ࢖ΘΕΔ w Double͸ʮഒਫ਼౓ුಈখ਺఺਺ʯͳͷͰɺਫ਼౓ͷ໰ ୊Ͱͦ΋ͦ΋ਖ਼֬ʹදͤͳ͍਺ࣈ͕ͨ͘͞Μ͋Δ w େ఍ͷ৔߹͸ͦͷؙΊΒΕͨ਺ࣈͰ΋໰୊ʹͳΒͳ͍ ͕ɺۚ༥ܥͳͲͷ৔߹͸ਖ਼֬ʹѻ͏ඞཁ͕͋Δ

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Decimal

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Decimalܕ w ුಈখ਺఺਺Λेਐ਺ϕʔεͰѻ͏ͨΊͷܕ w ༗ޮܻ਺͕ܻ w ༗ޮܻ਺ൣғ಺Ͱ͋Ε͹ेਐ਺දهͷޡ͕ࠩͳ͍

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// ࠓ݄ͷڅ༩ var myYumeCoin = 0.2 // ࠓ݄ͷϘʔφε myYumeCoin += 0.1 // ϘʔφεΛ࢖ͬͯങ͍෺ʂ myYumeCoin -= 0.1 // ࢒ߴ֬ೝ print(myYumeCoin) // 0.20000000000000004 ??????

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import Foundation // ࠓ݄ͷڅ༩ var myYumeCoin: Decimal = 0.2 // ࠓ݄ͷϘʔφε myYumeCoin += 0.1 // ϘʔφεΛ࢖ͬͯങ͍෺ʂ myYumeCoin -= 0.1 // ࢒ߴ֬ೝ print(myYumeCoin) // 0.2 🎉 'PVOEBUJPO͕ඞཁ ܕΛ໌ࣔతʹ%FDJNBMʹࢦఆ

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DecimalɺŜƃŤƄƃŬžŜŘŢŦ

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DecimalɺŜƃŤƄƃŬžŜŘŢŦ ͱɺࢥͬͨʁ

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import Foundation // ࠓ݄ͷڅ༩ var myYumeCoin: Decimal = 0.2 // ࠓ݄ͷϘʔφε myYumeCoin += 0.1 // ϘʔφεΛ࢖ͬͯങ͍෺ʂ myYumeCoin -= 0.1 // ࢒ߴ֬ೝ print(myYumeCoin) // 0.2 🎉

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import Foundation // ࠓ݄ͷڅ༩ var myYumeCoin: Decimal = 0.2 // ࠓ݄ͷϘʔφε myYumeCoin += 0.1 // ϘʔφεΛ࢖ͬͯങ͍෺ʂ myYumeCoin -= 0.1 // Decimal Λ࢖ͬͯਖ਼֬ͳڅ༩ܭࢉ͕Ͱ͖͔ͨΒ͍͑΍Ϙʔφεʂ myYumeCoin += 123.456 // ࢒ߴ֬ೝ print(myYumeCoin) // 123.65599999999997952 !!!?????

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DecimalɺūŬŹƂŜŽūŘ

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DecimalͷϦςϥϧ୅ೖ w খ਺ϦςϥϧͰDecimalΛ୅ೖͰ͖Δͷ͸ɺ ExpressibleByFloatLiteralΛར༻ͨ݁͠Ռ w ࣮૷͸init(floatLiteral value: Double) w DecimalΛ࡞Δલʹͦ΋ͦ΋ઌʹҰճDoubleΛ ࡞ͬͯͦͷ݁ՌΛ୅ೖ͍ͯ͠Δ͚ͩʂ

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খ਺ϦςϥϧͰ   DecimalΛ୅ೖ͠ͳ͍Ͱʂ

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%FDJNBMΛखܰʢʁʣʹѻ͏ͨΊͷ   ΠχγϟϥΠβʔ • init(_ value: String, format: Decimal.FormatStyle, lenient: Bool = true) throws // iOS 15+ • init?(string: String, locale: Locale? = nil) // iOS 7+ • // etc…

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import Foundation // … // Decimal Λ࢖ͬͯਖ਼֬ͳڅ༩ܭࢉ͕Ͱ͖͔ͨΒ͍͑΍Ϙʔφεʂ //myYumeCoin += 123.456 // ࠓ౓ͦ͜ʂ myYumeCoin += try! .init("123.456", format: .number) // ࢒ߴ֬ೝ print(myYumeCoin) // 123.656 🎉