# \[Returned for revision\] SE-0314 "AsyncStream and AsyncThrowingStream"

**URL:** <https://forums.swift.org/t/returned-for-revision-se-0314-asyncstream-and-asyncthrowingstream/49718>\
**Category:** Announcements\
**Created:** [June 17, 2021, 7:27pm UTC](https://forums.swift.org/t/returned-for-revision-se-0314-asyncstream-and-asyncthrowingstream/49718 "2021-06-17T19:27:10Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Douglas\_Gregor](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/douglas_gregor/32/1362_2.png) [@Douglas\_Gregor](https://forums.swift.org/u/Douglas_Gregor)\
**Post date:** [June 17, 2021, 7:27pm UTC](https://forums.swift.org/t/returned-for-revision-se-0314-asyncstream-and-asyncthrowingstream/49718/1 "2021-06-17T19:27:10Z")

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Hello Swift community,

The [review](https://forums.swift.org/t/se-0314-asyncstream-and-asyncthrowingstream/48198) of [SE-0314 "AsyncStream and AsyncThrowingStream"](https://github.com/apple/swift-evolution/blob/main/proposals/0314-async-stream.md) has concluded. The Core Team has decided to **return the proposal for revision** to address some concerns brought up in the review:

- Lack of support for back pressure. The `AsyncStream`/`AsyncThrowingStream` types themselves don't support back pressure.
- Unlimited buffer size by default: `Async(Throwing)Stream` default to having an unlimited buffer, although one can set a fixed buffer size (such that the oldest values will be dropped if the limit is hit) on creation.
- `AsyncThrowingStream` doesn't support typed errors: the other concurrency-related types we've introduced (task handles, task groups) have followed the precedent set by `Result` in having a typed error, even though the language `throws` mechanism doesn't support it. `AsyncThrowingStream` doesn't have a type for the error.

Because Juneteenth weekend is starting tomorrow, June 18, for many U.S. developers, I will schedule the next review to begin next Monday, June 21. The authors have already [provided an update](https://github.com/apple/swift-evolution/pull/1389) for the second review.

Thanks to everyone who participated in the review!

Doug