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Swiftのstructとイミュータビリティ
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Yuta Koshizawa
January 12, 2025
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Swiftのstructとイミュータビリティ
Yuta Koshizawa
January 12, 2025
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Transcript
Swi$ͷ struct ͱ ΠϛϡʔλϏϦςΟ @koher
ࣗݾհ • @koher • ΤϯδχΞʢQonceptʣ • ΧϯϑΝϨϯεొஃ • try! Swi0
Tokyo: 2016 • iOSDC Japan: 2017, 2018, 2019, 2020, 2021, 2022, 2024 • Swi0 Zoomin' ओ࠵ • Heart of Swi0 ࣥච
࣭ struct Foo { var value: Int } ͜ͷ struct
ϛϡʔλϒϧͰ͔͢ʁΠϛϡʔλϒϧͰ͔͢ʁ
struct ϛϡʔλϒϧͰ ຊ࣭తʹΠϛϡʔλϒϧΫϥεͱಉ͡
var ϓϩύςΟΛ࣋ͭ struct struct Foo { var value: Int }
var ϓϩύςΟΛ࣋ͭ struct struct Foo { var value: Int }
extension Foo { mutating func increment() { value += 1 } }
var ϓϩύςΟΛ࣋ͭ struct var foo: Foo = .init(value: 0) foo.increment()
print(foo.value) // 1
let ϓϩύςΟΛ࣋ͭ struct struct Foo { let value: Int }
let ϓϩύςΟΛ࣋ͭ struct struct Foo { let value: Int }
extension Foo { mutating func increment() { value += 1 // ⛔ ίϯύΠϧΤϥʔ } }
let ϓϩύςΟΛ࣋ͭ struct struct Foo { let value: Int }
extension Foo { mutating func increment() { self = Foo(value: value + 1) // ͜ΕͳΒOK } }
ϝιουͱ // ϝιουͷ߹ extension Foo { // ҉ͷୈ1Ҿ self Λ࣋ͭ
func bar() -> Int { self.value * self.value } }
ϝιουͱ // ϝιουͷ߹ extension Foo { // ҉ͷୈ1Ҿ self Λ࣋ͭ
func bar() -> Int { self.value * self.value } } let foo: Foo = .init(value: 3) print(foo.bar()) // 9
ϝιουͱ // ؔͷ߹ // ໌ࣔతୈ1Ҿ self Λ࣋ͭ func bar(_ self:
Foo) -> Int { self.value * self.value } let foo: Foo = .init(value: 3) print(bar(foo)) // 9
mutating ͱ struct Foo { var value: Int } extension
Foo { mutating func increment() { self.value += 1 // ✅ } }
mutating ͱ struct Foo { var value: Int } extension
Foo { func increment() { self.value += 1 // ⛔ } }
mutating ͱ struct Foo { var value: Int } func
increment(_ self: Foo) { self.value += 1 // ⛔ }
mutating ͱ struct Foo { var value: Int } func
increment(_ self: inout Foo) { self.value += 1 // ✅ }
mutating ͱ struct Foo { var value: Int } extension
Foo { mutating func increment() { self.value += 1 // ✅ } }
let ϓϩύςΟΛ࣋ͭ struct struct Foo { let value: Int }
extension Foo { mutating func increment() { self = Foo(value: self.value + 1) // } }
let ϓϩύςΟΛ࣋ͭ struct struct Foo { let value: Int }
func increment(_ self: inout Foo) { self = Foo(value: self.value + 1) // }
let ϓϩύςΟΛ࣋ͭ struct struct Foo { let value: Int }
extension Foo { mutating func increment() { self = Foo(value: self.value + 1) // } }
let ϓϩύςΟΛ࣋ͭ struct var foo: Foo = .init(value: 0) foo.increment()
// ✅ Foo.value ͕ let Ͱ OK print(foo.value) // 1
ϓϩύςΟͷએݴ͕ var ͔ let ͔ struct ͷϛϡʔλϏϦςΟΛܾΊͳ͍
มʢఆʣએݴͷ var / let ͕ struct ͷϛϡʔλϏϦςΟΛܾΊΔ
มʢఆʣએݴͱϛϡʔλϏϦςΟ var foo: Foo = .init(value: 0) foo.increment() // ✅
print(foo.value)
มʢఆʣએݴͱϛϡʔλϏϦςΟ let foo: Foo = .init(value: 0) foo.increment() // ⛔
print(foo.value)
ܕͷϛϡʔλϏϦςΟΛ ࢀরܕͱಉ͡Α͏ʹߟ͍͚͑ͯͳ͍
ܕͷΠϯελϯε มͷͨΊʹ֬อ͞ΕͨϝϞϦྖҬͱҰମ
ΠϛϡʔλϒϧΫϥε final class Foo { let value: Int }
ΠϛϡʔλϒϧΫϥε final class Foo { let value: Int } extension
Foo { // ⛔ ೦ͳ͕Β͜ΕSwiftͷߏจͷͰͰ͖ͳ͍ mutating func increment() { self = Foo(value: self.value + 1) } }
ΠϛϡʔλϒϧΫϥε final class Foo { let value: Int } //
✅ ͜ΕͳΒOK func increment(_ self: inout Foo) { self = Foo(value: self.value + 1) }
ΠϛϡʔλϒϧΫϥε var foo: Foo = .init(value: 0) increment(&foo) // ✅
͜ΕͳΒ foo ΛมߋՄ print(foo.value) // 1
struct ͱΠϛϡʔλϒϧΫϥε ຊ࣭తʹಉ͜͡ͱ͕Ͱ͖Δ
ΠϛϡʔλϒϧΫϥεΠϯελϯεͷ ϝϞϦྖҬΛมߋͰ͖ͳ͍
ࢀরܕͰͳ͘ܕͷ ʢมଆͷʣϛϡʔλϏϦςΟͰߟ͑Ε ΠϛϡʔλϒϧΫϥε struct ͱಉ͡
ϛϡʔλϒϧΫϥε final class Foo { var value: Int }
ϛϡʔλϒϧΫϥε final class Foo { var value: Int } extension
Foo { func increment() { value += 1 } }
ϛϡʔλϒϧΫϥε let foo: Foo = .init(value: 0) foo.increment() print(foo.value) //
1
ϛϡʔλϒϧΫϥε let foo: Foo = .init(value: 0) foo.increment() print(foo.value) //
1
ϛϡʔλϒϧΫϥε let foo: Foo = .init(value: 0) let foo2 =
foo foo.increment() print(foo.value) // 1
ϛϡʔλϒϧΫϥε let foo: Foo = .init(value: 0) let foo2 =
foo foo.increment() print(foo.value) // 1 print(foo2.value) // 1
struct var foo: Foo = .init(value: 0) var foo2 =
foo foo.increment() print(foo.value) // 1 print(foo2.value) // 0
ΠϛϡʔλϒϧΫϥε var foo: Foo = .init(value: 0) var foo2 =
foo increment(&foo) print(foo.value) // 1 print(foo2.value) // 0
struct ͱΠϛϡʔλϒϧΫϥε shared mutable stateΛ࣋ͨͳ͍
Sendable ४ڌ final class User: Sendable { // var name:
String } final class User: Sendable { // let name: String } struct User: Sendable { // ✅ var name: String }
struct Λ͑ϛϡʔλϒϧͰ ΠϛϡʔλϒϧΫϥεಉ༷ͷརӹΛڗडՄೳ
·ͱΊ • struct ຊ࣭తʹΠϛϡʔλϒϧΫϥεͱಉ͡ • struct Λ͑ϛϡʔλϒϧͰΠϛϡʔλϒϧΫϥεͱಉ ͡རӹΛڗडͰ͖Δ