swift - Running 3 functions serially each running when the previous function completes - Stack Overflow

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I'm trying to run 3 functions serially having each function complete before the next one starts. The below code works fine but I get three warnings on the try await [one, two, three] line:

1. No calls to throwing functions occur within try expression
2. No async operations occur within await expression
3. Expression of type [()] is unused.

Any suggestions on the proper way to code this and not get these warnings?

Task {
    let one: () = await func1()
    let two: ()  = await func2()
    let three: ()  = await func3()
    try await [one, two, three]
}

func func1() async { ... }
func func2() async { ... }
func func3() async { ... }

The functions essentially decode JSON data from separate external sources and then calculations are done on the results so its important each decoding happens before the next one starts.

I'm trying to run 3 functions serially having each function complete before the next one starts. The below code works fine but I get three warnings on the try await [one, two, three] line:

1. No calls to throwing functions occur within try expression
2. No async operations occur within await expression
3. Expression of type [()] is unused.

Any suggestions on the proper way to code this and not get these warnings?

Task {
    let one: () = await func1()
    let two: ()  = await func2()
    let three: ()  = await func3()
    try await [one, two, three]
}

func func1() async { ... }
func func2() async { ... }
func func3() async { ... }

The functions essentially decode JSON data from separate external sources and then calculations are done on the results so its important each decoding happens before the next one starts.

• swift
• async-await
• concurrency

Share Improve this question Follow edited Nov 16, 2024 at 18:44 Alexander 63.5k1313 gold badges105105 silver badges168168 bronze badges asked Nov 16, 2024 at 2:55 user1233894user1233894 1,77611 gold badge1212 silver badges1111 bronze badges 1

• These 3 functions are suspicious: if it's important that they run in a specific order, why is it that none of them take input, or return a result? Most people would expect to see something like let one = await func1(), let two = await func2(one), let three = await func3(two). That would make the dependency obvious, and impossible to get wrong. – Alexander Commented Nov 16, 2024 at 18:46

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1 Answer 1

Sorted by: Reset to default 1

It is simply:

Task {
    await func1()
    await func2()
    await func3()
}

That will run them consecutively. Just be wary of introducing additional unstructured concurrency (Task {…}) in those functions.

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