SE-0388 adds a new makeStream()
method to both AsyncStream
and AsyncThrowingStream
that sends back both the stream itself alongside its continuation.
So, rather than writing code like this:
var _continuation: AsyncStream<String>.Continuation!
let stream = AsyncStream<String> { continuation = $0 }
let continuation = _continuation!
We can now get both at the same time:
let (stream, continuation) = AsyncStream.makeStream(of: String.self)
This is going to be particularly welcome in places where you need to access the continuation outside of the current context, such as in a different method. For example, previously we might have written a simple number generator like this one, which needs to store the continuation as its own property in order to be able to call it from the queueWork()
method:
struct OldNumberGenerator {
private var continuation: AsyncStream<Int>.Continuation!
var stream: AsyncStream<Int>!
init() {
stream = AsyncStream(Int.self) { continuation in
self.continuation = continuation
}
}
func queueWork() {
Task {
for i in 1...10 {
try await Task.sleep(for: .seconds(1))
continuation.yield(i)
}
continuation.finish()
}
}
}
With the new makeStream(of:)
method this code becomes much simpler:
struct NewNumberGenerator {
let (stream, continuation) = AsyncStream.makeStream(of: Int.self)
func queueWork() {
Task {
for i in 1...10 {
try await Task.sleep(for: .seconds(1))
continuation.yield(i)
}
continuation.finish()
}
}
}
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