What's New in Swift

anyAppleOS Availability

Cross-platform APIs often repeat the same version gate five times. Swift 6.4 adds a shorthand for Apple platforms, which is especially useful in code shared across iOS, macOS, watchOS, tvOS, and visionOS.

@available(iOS 27, macOS 27, watchOS 27, tvOS 27, visionOS 27, *)
func showStatus() {
    // Same platform policy, older spelling.
}

@available(anyAppleOS 27, *)
func showStatus() {
    // Available on Apple's OS 27 family.
}

@available(anyAppleOS 27, *)
@available(tvOS, unavailable)
func launch() {
    // Same broad gate, with one platform exception.
}

The value is not just fewer characters. It makes the policy visible: this API belongs to the OS 27 family.

Sharper Diagnostics

Apple highlighted better Swift Concurrency diagnostics and a new @diagnose attribute for library authors who want more control over warnings. The theme is steady: move more mistakes from runtime review into compiler feedback.

Async Work in defer

Swift 6.4 supports asynchronous code in defer. That lets cleanup remain visually attached to the setup it balances, even when the cleanup itself needs suspension.

do {
    try await runOperation()
    await cleanup()
} catch {
    await cleanup()
    throw error
}

let landingTask = Task {
    try await lander.fly(to: moon)
}

defer {
    await orbiter.rendezvous(with: lander)
}

try await orbiter.wait(for: landingTask)

Expect this to show up around database transactions, file coordination, network teardown, and actor-owned resources.

Libraries: Testing, Subprocess, Foundation

The standard library and companion packages got quieter but meaningful polish. Swift Testing can be used more naturally from XCTest-based suites, which matters for projects that cannot migrate every test target at once. Subprocess reached a more mature 1.0 shape, including streamed output patterns.

final class RadioTests: XCTestCase {
    func testPingPacketTransmission() throws {
        let bytes = try checkedTransmitAndReceive(packet: .ping)
        #expect(bytes.count == 8)
    }
}

Foundation also keeps moving toward Swift-native implementations. Apple's Swift page calls out URL parsing gains of up to 4x, which is the kind of improvement server-side and data-heavy apps can feel without code changes.

Performance Without Leaving Swift

The performance story has two levels. First, Swift adds more explicit optimizer controls: @inline(always) for forced inlining and @specialized for important generic paths. Second, ownership features continue to reduce copies without falling back to unsafe pointers.

@inline(always)
func makeBuffer() -> [256 of Int] {
    InlineArray(repeating: 0)
}

@specialized(where Values == [UInt8])
func histogram<Values: Sequence>(of values: Values) -> [256 of Int]
where Values.Element == UInt8 {
    var buckets = makeBuffer()
    for value in values { buckets[Int(value)] += 1 }
    return buckets
}

Do not scatter these attributes everywhere. They are tools for measured hot paths where the compiler cannot see enough context on its own.

Beyond Apple Platforms

Swift's ecosystem work is increasingly visible. The WWDC session called out the first Swift SDK for Android in Swift 6.3, ongoing WebAssembly and JavaScriptKit improvements, Swift-Java work, Windows progress, and continued Embedded Swift investment.

For Apple app teams, the practical takeaway is shared domain code. Swift is no longer only a UI-app language for Apple clients; it is becoming a more credible cross-platform systems and application language.

Adoption Checklist