I need to store the AsyncIterator of a ThrowingTaskGroup for later use. I’m creating this iterator inside of an async function inside of an actor. However, as the resulting iterator is a value type, I cannot store and later access it outside of the scope of the current function.
Is there something inherently wrong with my approach?

Here’s some code to illustrate the issue:

actor Foo {
    private var iterator: ThrowingTaskGroup<String, any Error>.Iterator?

    func bar() async throws {
        let workItems = ["A", "B", "C", "D"]

        try await withThrowingTaskGroup(of: String.self) { group in
            workItems.forEach { item in
                group.addTask { [unowned self] in
                    return try await doWork(on: item)
                }
            }

            iterator = group.makeAsyncIterator()

            guard let firstItem = try await iterator?.next() else { // Cannot call mutating async function 'next()' on actor-isolated property 'iterator'
                throw "An error"
            }

            // do some work based on first item
        }
    }

    private func atALaterPointInTime() async throws {
        while let item = try await iterator?.next() { // Cannot call mutating async function 'next()' on
            await doMoreWork(on: item)
        }
    }

    private func doWork(on item: String) async throws -> String {
        return item
    }

    private func doMoreWork(on item: String) async {
        // ...
    }
}