withThrowingTaskGroup - No calls to throwing functions occur within 'try' expression

Hi,

Problem:

I have the following function which shows a warning No calls to throwing functions occur within 'try' expression

Questions:

  • Why is this warning shown? (The code inside the task throws an error)
  • What should I do to propagate the error to the caller of f1?

Code:

func f1() async throws {
    try await withThrowingTaskGroup(of: Int.self) { group in //No calls to throwing functions occur within 'try' expression
        group.addTask(priority: .high) {
            throw NSError()
        }
    }
}

No, the code inside the closure passed to group.addTask throws. The closure passed to withThrowingTaskGroup does not throw, so calling withThrowingTaskGroup with the try keyword produces a warning.

2 Likes

Thanks @Peter-Schorn so is calling try await group.waitForAll() as shown below the right way to escalate the error to f1?

func f1() async throws {
    try await withThrowingTaskGroup(of: Int.self) { group in
        group.addTask(priority: .high) {
            throw NSError(domain: "testing error", code: 21, userInfo: nil)
        }
        
        try await group.waitForAll()
    }
}

Yes, that will cause the error to be thrown to the caller of f1

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