init(_:bufferingPolicy:_:)

Declaration

init(_ elementType: Element.Type = Element.self, bufferingPolicy limit: AsyncStream<Element>.Continuation.BufferingPolicy = .unbounded, _ build: (AsyncStream<Element>.Continuation) -> Void)

Parameters

• elementType:

  The type of element the AsyncStream produces.

• limit:

  A Continuation.BufferingPolicy value to set the stream’s buffering behavior. By default, the stream buffers an unlimited number of elements. You can also set the policy to buffer a specified number of oldest or newest elements.

• build:

  A custom closure that yields values to the AsyncStream. This closure receives an AsyncStream.Continuation instance that it uses to provide elements to the stream and terminate the stream when finished.

Discussion

The AsyncStream.Continuation received by the build closure is appropriate for use in concurrent contexts. It is thread safe to send and finish; all calls to the continuation are serialized. However, calling this from multiple concurrent contexts could result in out-of-order delivery.

The following example shows an AsyncStream created with this initializer that produces 100 random numbers on a one-second interval, calling yield(_:) to deliver each element to the awaiting call point. When the for loop exits, the stream finishes by calling the continuation’s finish() method.

let stream = AsyncStream<Int>(Int.self,
                              bufferingPolicy: .bufferingNewest(5)) { continuation in
    Task.detached {
        for _ in 0..<100 {
            await Task.sleep(1 * 1_000_000_000)
            continuation.yield(Int.random(in: 1...10))
        }
        continuation.finish()
    }
}

// Call point:
for await random in stream {
    print(random)
}

See Also

Creating a Continuation-Based Stream

• AsyncStream.Continuation.BufferingPolicy
• AsyncStream.Continuation