# next(isolation:) The next value from the asynchronous stream. ``` mutating func next(isolation actor: isolated (any Actor)?) async -> Element? ``` ## Discussion When `next()` returns `nil`, this signifies the end of the `AsyncStream`. It is a programmer error to invoke `next()` from a concurrent context that contends with another such call, which results in a call to `fatalError()`. If you cancel the task this iterator is running in while `next()` is awaiting a value, the `AsyncStream` terminates. In this case, `next()` might return `nil` immediately, or return `nil` on subsequent calls. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)