swift-async

Composable asynchronous streams and isolation-preserving AsyncSequence operators for Swift, built around a concrete Async.Stream type that composes through reactive combinators without type erasure.

---

Key Features

• Concrete Async.Stream<Element> — a single Sendable AsyncSequence type that can be stored, passed around, and composed without any AsyncSequence erasure or generic type explosion.
• Reactive combinators — merge, zip, combine.latest, debounce, throttle, sample, scan, delay, and timeout over the concrete stream type.
• Multicast — share() and replay give multiple consumers a single upstream subscription instead of one per for await.
• Isolation-preserving sequence operators — map, filter, compactMap, and flatMap overloads that accept synchronous closures and run inline on the caller's actor rather than hopping to the cooperative pool.
• Nested-accessor API — variant transforms live under accessors (stream.map.compact, stream.map.flat.latest, stream.zip(other)) instead of compound method names.
• Stream constructors — build a stream from a sequence, an interval, a timer, or any existing AsyncSequence via .from, .interval, .just, .empty, and .never.

---

Quick Start

A stream assembled from an interval and a stream built from a literal sequence are the same concrete type — Async.Stream<String> — so merge composes them uniformly. Without a concrete stream type, combining heterogeneously-constructed async sequences forces any AsyncSequence erasure or a bespoke merging AsyncIteratorProtocol:

import Async

let ticks = Async.Stream.interval(.seconds(1))
    .map { "tick #\($0)" }                  // Async.Stream<String>

let messages = Async.Stream.from(["ping", "pong"])  // Async.Stream<String>

let merged = Async.Stream.merge(ticks, messages)    // Async.Stream<String>

for await line in merged {
    print(line)
}

---

Installation

dependencies: [
    .package(url: "https://github.com/swift-foundations/swift-async.git", branch: "main")
]

.target(
    name: "YourTarget",
    dependencies: [
        .product(name: "Async", package: "swift-async")
    ]
)

Requires Swift 6.3.1 and macOS 26 / iOS 26 / tvOS 26 / watchOS 26 / visionOS 26.

---

Architecture

The Async umbrella product re-exports the stream type, the sequence operators, and the underlying async coordination primitives. Narrower products are available when only one surface is needed.

Product	Import	When to import
Async	import Async	The umbrella — the concrete stream type, the AsyncSequence operators, and the coordination primitives in one import.
Async Sequence	import Async_Sequence	Only the isolation-preserving lazy operators (map / filter / compactMap / flatMap) over any AsyncSequence.
Async Stream	import Async_Stream	Only the concrete Async.Stream type and its reactive combinators.
Async Test Support	import Async_Test_Support	Test targets exercising async streams.

---

Community

Discussion thread will be created at first public release.

License

Apache 2.0. See LICENSE.