Possible to return an AsyncSequence<T> for iOS 17 when building against iOS 18?

[vanvoorden (Rick van Voorden)]

How to use `AsyncSequence` on macOS 14.5 in Xcode 16 beta? Need help with availability check since `Failure` is unavailb.e

This seems to compile from 6.0 and deploys (runs) on macOS 14. public protocol EmitterProtocol<Element, Failure> { associatedtype Element where Self.Sequence.Element == Element @available(macOS 15.0, *) associatedtype Failure : Error = any Error where Self.Sequence.Failure == Failure associatedtype Sequence : AsyncSequence func notifications() -> Sequence } public final class Emitter : EmitterProtocol { let (stream, continuation) = AsyncStream<Int>.makeStream() public func no…

I'm still using this for a workaround. Instead of returning an opaque (or erased) AsyncSequence… my idea here is to box a concrete AsyncSequence in an opaque Container. The extra layer of indirection seems to help keep the compiler happy.