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.

let stream = Counter(howHigh: 5)
    .flatMap { Counter(howHigh: $0) }
for await number in stream {
    print(number, terminator: " ")
}
// Prints "1 1 2 1 2 3 1 2 3 4 1 2 3 4 5 "