ObservationKit

A small library that aims to make it possible for me to adopt the Observation framework now, instead of years in the future.

ObservationShim

This is a copy of SwiftLang's Observations.swift with some small tweaks to enable iOS 17+ compatibility. There are endless online discussions and dozens of projects that aim to enable the use of AsyncSequence and modern concurrency based streaming tools in favor of Combine. This one clicked thanks to this Swift Forums post iOS 18 support for the Observations struct is being dropped before release?.

Important

This is not aimed at replacing Observations. It's simply a shim you can use to start making real use of the Apple Observations framework in favor of a bunch of bridges to other data sources like Combine

This example shows how you'd effectively erase the official and shimmed backport into an AsyncStream to use outside of SwiftUI. Note Pointfree Co's ConcurrencyExtras was used to allow erasure into a clean AsyncStream<Element>.

func observableStream(
    _ emit: @escaping @isolated(any) @Sendable () -> Element
) -> AsyncStream<Element> {
    if #available(iOS 26.0, *) {
        let official = Observations(emit)
        return AsyncStream(official)
    } else {
        let backport = ObservationsShim(emit)
        return AsyncStream(backport)
    }
}

References

• @vanvoorden iOS 18 support for the Observations struct is being dropped before release?
• @phausler iOS 18 support for the Observations struct is being dropped before release?
• Observations.swift

ObservationTesting

Swift Testing introduced a new paradigm for async confirmation in Testing asyncronous code. The swift tools are totally acceptable, but can be quite verbose and a bit tricky, especially testing outputs from AsyncSequences. The ObservationTesting library enables concise unit tests for AsyncSequences. This also works really well with Observations and ObservationsShim.

This includes verifying Equatable elements over time.

@Test("A value is emitted from the stream")
func basic() async throws {
    let stream = AsyncStream { continuation in
        continuation.yield("cats")
        continuation.yield("dogs")
        continuation.yield("lizards")
    }
    
    try await stream.fulfillment(of: "cats", "dogs", "lizards")
}

Or complex conditions that can't easily be represented as expected value(s).

@Test("A condition is verified on the stream")
func conditionMet() async throws {
    let stream = AsyncStream { continuation in
        continuation.yield("cats")
    }
    
    try await stream.fulfillment { value in
        value == "cats"
    }
}