在Swift 5.5中组成同步和异步功能

发布于 2025-02-14 00:30:22 字数 322 浏览 1 评论 0原文

考虑以下（愚蠢的）示例：

func u () async -> UInt32 {
    let r =  UInt32(Int.random(in: 1...10))
    sleep(r)
    return r
}

func v(_ x: UInt32) -> UInt32 {
    x
}

Task.init{
    print(v(await u()))
    print(await v(u()))
    await print(v(u()))
}

任务中的所有三行似乎都起作用。它们是等效的，还是我应该知道任何陷阱？谢谢。

原文

Consider the following (silly) example:

func u () async -> UInt32 {
    let r =  UInt32(Int.random(in: 1...10))
    sleep(r)
    return r
}

func v(_ x: UInt32) -> UInt32 {
    x
}

Task.init{
    print(v(await u()))
    print(await v(u()))
    await print(v(u()))
}

All three lines in the task appear to work. Are they equivalent, or are there any pitfalls I should be aware of? Thanks.

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格子衫的從容 2025-02-21 00:30:22

喜欢尝试，Swift允许您将等待关键字放在表达式的任何部分，其中包含async方法：

func ƒ<T>(_ v: T) -> T { v }


// All equivalent:
func somethingThatThrows() throws {}
print(ƒ(try somethingThatThrows()))
print(try ƒ(somethingThatThrows()))
try print(ƒ(somethingThatThrows()))


// All equivalent:
func someAsyncFunc() async {}
Task {
    print(ƒ(await someAsyncFunc()))
    print(await ƒ(someAsyncFunc()))
    await print(ƒ(someAsyncFunc()))
}

// await applies to both function calls
sum = await someAsyncFunction() + anotherAsyncFunction()

// await applies to both function calls
sum = await (someAsyncFunction() + anotherAsyncFunction())

// Error: await applies only to the first function call
sum = (await someAsyncFunction()) + anotherAsyncFunction()

Like try, Swift allows you to place the await keyword on any part of an expression that contains an async method:

func ƒ<T>(_ v: T) -> T { v }


// All equivalent:
func somethingThatThrows() throws {}
print(ƒ(try somethingThatThrows()))
print(try ƒ(somethingThatThrows()))
try print(ƒ(somethingThatThrows()))


// All equivalent:
func someAsyncFunc() async {}
Task {
    print(ƒ(await someAsyncFunc()))
    print(await ƒ(someAsyncFunc()))
    await print(ƒ(someAsyncFunc()))
}

The Swift grammar reference for the await keyword does have an example for where placement of await does matter (awaiting only a subexpression of a whole expression that needs to be awaited), but it's not quite relevant here:

// await applies to both function calls
sum = await someAsyncFunction() + anotherAsyncFunction()

// await applies to both function calls
sum = await (someAsyncFunction() + anotherAsyncFunction())

// Error: await applies only to the first function call
sum = (await someAsyncFunction()) + anotherAsyncFunction()

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