先取り！ Swift 6 の async/await

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ઌऔΓʂSwi$ 6 ͷ async/await Yuta Koshizawa @koher

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SE-0296: Async/await4 4 h$ps:/ /github.com/apple/swi6-evolu9on/blob/main/proposals/0296-async-await.md

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Swi$ ͷඇಉظॲཧʢ͜Ε·Ͱʣ func download(from url: URL, completion: @escaping (Data) -> Void) download(from: url) { data in // ͜͜Ͱඇಉظʹड͚औͬͨ data Λ࢖͏ }

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Swi$ ͷඇಉظॲཧʢ͜Ε͔Βʣ func download(from url: URL) async -> Data let data = await download(from: url) // ͜͜Ͱඇಉظʹड͚औͬͨ data Λ࢖͏

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throws/try func foo() throws {} func bar() { try foo() // ⛔ }

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throws/try func foo() throws {} func bar() throws { try foo() // ✅ }

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async/await func foo() async {} func bar() { await foo() // ⛔ }

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async/await func foo() async {} func bar() async { await foo() // ✅ }

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Poten&al Suspension Point func download(from url: URL) async -> Data func downloadImage(from url: URL) async -> UIImage { // Potential Suspension Point let data = await download(from: url) // (A) let image = UIImage(data: data)! // (B) return image }

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RPG ͷྫͱϒϩοΩϯά

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RPG ͷྫͱϒϩοΩϯά func performTurn(of character: Character) { ... switch action { ... case .spell: // (1) ຐ๏Λબ୒ let spell = selectSpell(of: character) // (2) ຐ๏Λ͔͚Δ૬खΛબ୒ let target = selectTarget(of: spell) // (3) ຐ๏Λ࣮ߦ perform(spell, on: target) } }

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RPG ͷྫͱϒϩοΩϯά func performTurn(of character: Character) async { ... switch action { ... case .spell: // (1) ຐ๏Λબ୒ let spell = await selectSpell(of: character) // (2) ຐ๏Λ͔͚Δ૬खΛબ୒ let target = await selectTarget(of: spell) // (3) ຐ๏Λ࣮ߦ await perform(spell, on: target) } }

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ίʔϧόοΫ஍ࠈ foo { a in bar(a) { b in baz(b) { c in qux(c) { d in self.x = d } } } }

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async/await ͳΒ let a = await foo() let b = await bar(a) let c = await baz(b) let d = await qux(c) self.x = d

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Future ͩͱ foo().flatMap { a in bar(a) }.flatMap { b in baz(b) }.flatMap { c in qux(c) }.sink { d in self.x = d }.store(in: &cancellables)

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੍ޚߏ଄ͱͷ૊Έ߹Θͤ let x = await foo() var sum = 0 while x > 0 { sum += x x = await bar(x) if x.isMultiple(of: 2) { return nil } } return sum

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࿅श໰୊

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໰୊ 01A h"ps:/ /swi)ﬁddle.com/m7nn4xoim62xdk7p5htbxmmau ໰୊ 01B h"ps:/ /swi)ﬁddle.com/zvnt3mp5tvgbbkd5mq5n3fvynm

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Τϥʔ͕ى͜ΓಘΔ৔߹ʢίʔϧόοΫʣ func download(from url: URL, completion: @escaping (Result) -> Void) download(from: url) { result in do { let data: Data = try result.get() // ͜͜Ͱ data Λ࢖͏ } catch { // ͜͜ͰΤϥʔॲཧΛߦ͏ } }

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Τϥʔ͕ى͜ΓಘΔ৔߹ʢ async/await ʣ func download(from url: URL) async throws -> Data do { let data = try await download(from: url) // ͜͜Ͱ data Λ࢖͏ } catch { // ͜͜ͰΤϥʔॲཧΛߦ͏ }

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໰୊ 02A h"ps:/ /swi)ﬁddle.com/g7gvhfdug5hurbre2nzhifshaa ໰୊ 02B h"ps:/ /swi)ﬁddle.com/2si365hypvbd7pw27mp7hhibkm

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໰୊ 03A h"ps:/ /swi)ﬁddle.com/5wnkjwkrzvhptlvhy7iukkfue4 ໰୊ 03B h"ps:/ /swi)ﬁddle.com/nbdwkt4yjzb23b33236wr5oj?

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ฒߦॲཧʁ let a = await foo() let b = await bar() print(a + b)

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ฒߦॲཧ async let a = foo() async let b = bar() print(await a + b)

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ฒߦॲཧʢ JS ʣʁ const a = await foo(); // number const b = await bar(); // number console.log(a + b);

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ฒߦॲཧʢ JS ʣ const a = foo(); // Promise const b = bar(); // Promise console.log(await a + await b);

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ฒߦॲཧʢ Swi% ʣ async let a = foo() // Int async let b = bar() // Int print(await a + b)

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inout func foo(_ x: inout Int) -> () -> Int { let bar: () -> Int = { return x + 1 } // return bar } var a = 42 let bar = foo(&a) a += 1 print(bar())

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Structured concurrency5 The concept was formulated in 2016 by Mar7n Sústrik ..., and then further reﬁned in 2018 by Nathaniel J. Smith, ... Meanwhile, Roman Elizarov independently came upon the same ideas while developing an experimental corou7ne library for the Kotlin language. In 2019, the loom project from OpenJDK is adop8ng structured concurrency ... In 2020, Swi? is men8oning adop8on of structured concurrency in their concurrency roadmap. 5 h$ps:/ /en.wikipedia.org/wiki/Structured_concurrency

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SE-NNNN: Structured concurrency6 6 h$ps:/ /github.com/DougGregor/swi7-evolu;on/blob/structured-concurrency/proposals/nnnn-structured- concurrency.md

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໰୊ 04 h"ps:/ /swi)ﬁddle.com/dgvmmmc4fax8yu6474p37ke

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async ͷࠜͬ͜ func foo() async {} func bar() { await foo() // ⛔ }

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async ͷࠜͬ͜ • τοϓϨϕϧ • @main • @asyncHandler • Task.runDetached • ( runAsyncAndBlock )

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τοϓϨϕϧ await foo() await bar() await baz()

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runAsyncAndBlock runAsyncAndBlock { await foo() await bar() await baz() }

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@asyncHandler func foo() async {} @asyncHandler func bar() { await foo() }

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@asyncHandler @asyncHandler func bar() { print(2) await foo1() print(4) await foo2() print(5) } print(1) bar() print(3)

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async // @asyncHandler func bar() async { print(2) await foo1() print(3) await foo2() print(4) } print(1) await bar() print(5)

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໰୊ 05 h"ps:/ /swi)ﬁddle.com/rhtpvch3rreovbcgw757c3keem

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@asyncHandler func foo() async {} @asyncHandler func bar() { await foo() }

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Task.runDetached func foo() async {} func bar() { Task.runDetached { await foo() } }

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Task.runDetached func foo() async {} func bar() { let handle = Task.runDetached { await foo() } handle.cancel() }

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Task func foo() async { // Thread A await bar() // Thread B await baz() // Threac C }

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Task func foo() async { // Task A await bar() // Task A await baz() // Task A }

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Child Task func foo() async -> Int { // Task A async let a = bar() // Task A async let b = baz() // Task A return await a + b }

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Child Task func bar() async -> Int { // Task A' ... } func bar() async -> Int { // Task A'' ... }

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Child Task func foo() async -> Int { // Task A async let a = bar() // Task A async let b = baz() // Task A return await a + b }

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Task Tree શମͷΩϟϯηϧ func foo() async { // ෳࡶͳ Task Tree Λ࣋ͭඇಉظॲཧ } func bar() { let handle = Task.runDetached { await foo() } handle.cancel() }

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໰୊ 06 h"ps:/ /swi)ﬁddle.com/mwjiy2f768ztaagrfrqs6lxhy

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ίʔϧόοΫ → async func foo(completion: @escaping (Int) -> Void) { ... } func foo() async -> Int { // ίʔϧόοΫ൛ͷ foo Λ࢖ͬͯͲ͏΍࣮ͬͯ૷͢Δʁ }

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ίʔϧόοΫ → async ʢ JS ʣ function fooCallback(completion) { ... } function fooAsync() { return new Promise((resolve) => { fooCallback(value => { resolve(value); }); }); }

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ίʔϧόοΫ → async ʢ Swi& ʣ func foo(completion: @escaping (Int) -> Void) { ... } func foo() async -> Int { await withUnsafeContinuation { continuation in foo { value in continuation.resume(returning: value) } } }

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SE-0300: Con+nua+ons for interfacing async tasks with synchronous code7 7 h$ps:/ /github.com/apple/swi6-evolu9on/blob/main/proposals/0300-con9nua9on.md

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Con$nua$on • UnsafeContinuation • UnsafeThrowingContinuation • CheckedContinuation • CheckedThrowingContinuation

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UnsafeContinuation withUnsafeContinuation Ͱड͚औΔɻ struct UnsafeContinuation { func resume(returning: T) }

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UnsafeThrowingContinuation withUnsafeThrowingContinuation Ͱड͚औΔɻ struct UnsafeThrowingContinuation { func resume(returning: T) func resume(throwing: Error) func resume(with result: Result) }

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໰୊ 07 h"ps:/ /swi)ﬁddle.com/tuu5w2k37jdu5:k6gv5>hcni

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·ͱΊ • async/await (Accepted) • async let • @asyncHandler • Task.Handle • Con&nua&on (Ac)ve review)