ControlNotificationStream.flatMap(_:)

Use this method to receive a single-level asynchronous sequence when your transformation produces an asynchronous sequence for each element.

In this example, an asynchronous sequence called Counter produces Int values from 1 to 5. The transforming closure takes the received Int and returns a new Counter that counts that high. For example, when the transform receives 3 from the base sequence, it creates a new Counter that produces the values 1, 2, and 3. The flatMap(_:) method "flattens" the resulting sequence-of-sequences into a single AsyncSequence. However, when the closure receives 4, it throws an error, terminating the sequence.

do { let stream = Counter(howHigh: 5) .flatMap { (value) -> Counter in if value == 4 { throw MyError() } return Counter(howHigh: value) } for try await number in stream { print(number, terminator: " ") } } catch { print(error) } // Prints "1 1 2 1 2 3 MyError() "

• Parameter transform: An error-throwing mapping closure. transform accepts an element of this sequence as its parameter and returns an AsyncSequence. If transform throws an error, the sequence ends.
• Returns: A single, flattened asynchronous sequence that contains all elements in all the asynchronous sequences produced by transform. The sequence ends either when the last sequence created from the last element from base sequence ends, or when transform throws an error.