Flesh out the readme and add more tests

Readme.md

@@ -12,6 +12,87 @@ It uses a Swift `Task` to ensure that all resources are properly cleaned up when
 
 That's it. It's pretty trivial. I just got tired of writing it over and over, mainly for notifications. You still have to map your `Notification`s to something sendable.
 
+## Usage
+
+The simplest example uses a closure that receives the notification. The closure is async so you can await in there if you need to.
+
+```swift
+import AsyncMonitor
+
+class SimplestVersion {
+    let cancellable = NotificationCenter.default
+        .notifications(named: .NSCalendarDayChanged)
+        .map(\.name)
+        .monitor { _ in
+            print("The date is now \(Date.now)")
+        }
+}
+```
+
+This example uses the context parameter to avoid reference cycles with `self`.
+
+```swift
+class WithContext {
+    var cancellables = Set<AnyAsyncCancellable>()
+
+    init() {
+        NotificationCenter.default
+            .notifications(named: .NSCalendarDayChanged)
+            .map(\.name)
+            .monitor(context: self) { _self, _ in
+                _self.dayChanged()
+            }.store(in: &cancellables)
+    }
+
+    func dayChanged() {
+        print("The date is now \(Date.now)")
+    }
+}
+```
+
+### Combine
+
+Working with Combine publishers is trivial thanks to [`AnyPublisher.values`][values].
+
+```swift
+import Combine
+
+class CombineExample {
+    var cancellables = Set<AnyAsyncCancellable>()
+
+    init() {
+        Timer.publish(every: 1.0, on: .main, in: .common)
+            .autoconnect()
+            .values
+            .monitor { date in
+                print("Timer fired at \(date)")
+            }
+            .store(in: &cancellables)
+    }
+}
+```
+
+[values]: https://developer.apple.com/documentation/combine/anypublisher/values-3s2uy
+
+### Key-Value Observing (KVO) extension
+
+When you need to observe an object that uses [KVO][] there's an extension method you can use to monitor it:
+
+```swift
+class KVOExample {
+    var cancellables = Set<AnyAsyncCancellable>()
+
+    init() {
+        let progress = Progress(totalUnitCount: 42)
+        progress.values(for: \.fractionCompleted) { fraction in
+            print("Progress is \(fraction.formatted(.percent))%")
+        }.store(in: &cancellables)
+    }
+}
+```
+
+[KVO]: https://developer.apple.com/library/archive/documentation/General/Conceptual/DevPedia-CocoaCore/KVO.html
+
 ## Installation
 
 The only way to install this package is with Swift Package Manager (SPM). Please [file a new issue][] or submit a pull-request if you want to use something else.
@@ -36,46 +117,6 @@ When you're integrating this using SPM on its own then add this to the list of d
 
 and then add `"AsyncMonitor"` to the list of dependencies in your target as well.
 
-## Usage
-
-The simplest example uses a closure that receives the notification:
-
-```swift
-import AsyncMonitor
-
-class SimplestVersion {
-    let cancellable = NotificationCenter.default
-        .notifications(named: .NSCalendarDayChanged).map(\.name)
-        .monitor { _ in
-            print("The date is now \(Date.now)")
-        }
-}
-```
-
-This example uses the context parameter to avoid reference cycles with `self`:
-
-```swift
-import AsyncMonitor
-
-class WithContext {
-    var cancellables = Set<AnyAsyncCancellable>()
-
-    init() {
-        NotificationCenter.default
-            .notifications(named: .NSCalendarDayChanged).map(\.name)
-            .monitor(context: self) { _self, _ in
-                _self.dayChanged()
-            }.store(in: &cancellables)
-    }
-
-    func dayChanged() {
-        print("The date is now \(Date.now)")
-    }
-}
-```
-
-The closure is async so you can await in there if you need to.
-
 ## License
 
 Copyright © 2025 [Sami Samhuri](https://samhuri.net) <sami@samhuri.net>. Released under the terms of the [MIT License][MIT].

Sources/AsyncMonitor/AnyAsyncCancellable.swift

@@ -1,6 +1,8 @@
 /// Type-erasing wrapper for ``AsyncCancellable`` that ties its instance lifetime to cancellation. In other words, when you release
 /// an instance of ``AnyAsyncCancellable`` and it's deallocated then it automatically cancels its given ``AsyncCancellable``.
 public class AnyAsyncCancellable: AsyncCancellable {
+    lazy var id = ObjectIdentifier(self)
+
     let canceller: () -> Void
 
     public init<AC: AsyncCancellable>(cancellable: AC) {
@@ -16,4 +18,14 @@ public class AnyAsyncCancellable: AsyncCancellable {
     public func cancel() {
         canceller()
     }
+
+    // MARK: Hashable conformance
+
+    public static func == (lhs: AnyAsyncCancellable, rhs: AnyAsyncCancellable) -> Bool {
+        lhs.id == rhs.id
+    }
+
+    public func hash(into hasher: inout Hasher) {
+        hasher.combine(id)
+    }
 }

Sources/AsyncMonitor/AsyncCancellable.swift

@@ -15,15 +15,3 @@ public extension AsyncCancellable {
         set.insert(AnyAsyncCancellable(cancellable: self))
     }
 }
-
-// MARK: Hashable conformance
-
-public extension AsyncCancellable {
-    static func == (lhs: Self, rhs: Self) -> Bool {
-        ObjectIdentifier(lhs) == ObjectIdentifier(rhs)
-    }
-
-    func hash(into hasher: inout Hasher) {
-        hasher.combine(ObjectIdentifier(self))
-    }
-}

Sources/AsyncMonitor/AsyncMonitor.swift

@@ -5,7 +5,8 @@
 ///
 /// ```
 /// NotificationCenter.default
-///     .notifications(named: .NSCalendarDayChanged).map(\.name)
+///     .notifications(named: .NSCalendarDayChanged)
+///     .map(\.name)
 ///     .monitor { _ in whatever() }
 ///     .store(in: &cancellables)
 /// ```
@@ -43,4 +44,14 @@ public final class AsyncMonitor: Hashable, AsyncCancellable {
     public func cancel() {
         task.cancel()
     }
+
+    // MARK: Hashable conformance
+
+    public static func == (lhs: AsyncMonitor, rhs: AsyncMonitor) -> Bool {
+        lhs.task == rhs.task
+    }
+
+    public func hash(into hasher: inout Hasher) {
+        hasher.combine(task)
+    }
 }

Sources/AsyncMonitor/NSObject+AsyncKVO.swift

@@ -18,8 +18,12 @@ public extension NSObjectProtocol where Self: NSObject {
         let token = self.observe(keyPath, options: options) { object, _ in
             continuation.yield(object[keyPath: keyPath])
         }
+        let locker = TokenLocker(token: token)
+        continuation.onTermination = { _ in
+            locker.clear()
+        }
         return stream.monitor { value in
-            _ = token // keep this alive
+            _ = locker // keep this alive
             changeHandler(value)
         }
     }

Sources/AsyncMonitor/TokenLocker.swift

@@ -0,0 +1,16 @@
+import Foundation
+
+final class TokenLocker: @unchecked Sendable {
+    private let lock = NSLock()
+    private var unsafeToken: NSKeyValueObservation?
+
+    init(token: NSKeyValueObservation) {
+        unsafeToken = token
+    }
+
+    func clear() {
+        lock.withLock {
+            unsafeToken = nil
+        }
+    }
+}

Tests/AsyncMonitorTests/AnyAsyncCancellableTests.swift

@@ -0,0 +1,22 @@
+@testable import AsyncMonitor
+import Testing
+
+@MainActor class AnyAsyncCancellableTests {
+    var subject: AnyAsyncCancellable!
+
+    @Test func cancelsWhenReleased() {
+        let cancellable = TestCancellable()
+        subject = AnyAsyncCancellable(cancellable: cancellable)
+        #expect(!cancellable.isCancelled)
+        subject = nil
+        #expect(cancellable.isCancelled)
+    }
+
+    @Test func cancelsWhenCancelled() {
+        let cancellable = TestCancellable()
+        subject = AnyAsyncCancellable(cancellable: cancellable)
+        #expect(!cancellable.isCancelled)
+        subject.cancel()
+        #expect(cancellable.isCancelled)
+    }
+}

Tests/AsyncMonitorTests/AsyncCancellableTests.swift

@@ -0,0 +1,17 @@
+@testable import AsyncMonitor
+import Testing
+
+@MainActor class AsyncCancellableTests {
+    var cancellables = Set<AnyAsyncCancellable>()
+
+    @Test func storeInsertsIntoSetAndKeepsSubjectAlive() throws {
+        var subject: TestCancellable? = TestCancellable()
+        weak var weakSubject: TestCancellable? = subject
+        try #require(subject).store(in: &cancellables)
+        #expect(cancellables.count == 1)
+        subject = nil
+        #expect(weakSubject != nil)
+        cancellables.removeAll()
+        #expect(weakSubject == nil)
+    }
+}

Tests/AsyncMonitorTests/AsyncMonitorTests.swift

@@ -10,10 +10,12 @@ class AsyncMonitorTests {
 
     @Test func callsBlockWhenNotificationsArePosted() async throws {
         await withCheckedContinuation { [center, name] continuation in
-            subject = center.notifications(named: name).map(\.name).monitor { receivedName in
-                #expect(name == receivedName)
-                continuation.resume()
-            }
+            subject = center.notifications(named: name)
+                .map(\.name)
+                .monitor { receivedName in
+                    #expect(name == receivedName)
+                    continuation.resume()
+                }
             Task {
                 center.post(name: name, object: nil)
             }
@@ -21,9 +23,11 @@ class AsyncMonitorTests {
     }
 
     @Test func doesNotCallBlockWhenOtherNotificationsArePosted() async throws {
-        subject = center.notifications(named: name).map(\.name).monitor { receivedName in
-            Issue.record("Called for irrelevant notification \(receivedName)")
-        }
+        subject = center.notifications(named: name)
+            .map(\.name)
+            .monitor { receivedName in
+                Issue.record("Called for irrelevant notification \(receivedName)")
+            }
         Task { [center] in
             center.post(name: Notification.Name("something else"), object: nil)
         }
@@ -31,9 +35,11 @@ class AsyncMonitorTests {
     }
 
     @Test @MainActor func stopsCallingBlockWhenDeallocated() async throws {
-        subject = center.notifications(named: name).map(\.name).monitor { _ in
-            Issue.record("Called after deallocation")
-        }
+        subject = center.notifications(named: name)
+            .map(\.name)
+            .monitor { _ in
+                Issue.record("Called after deallocation")
+            }
 
         Task { @MainActor in
             subject = nil
@@ -51,7 +57,8 @@ class AsyncMonitorTests {
         init(center: NotificationCenter, deinitHook: @escaping () -> Void) {
             self.deinitHook = deinitHook
             let name = Notification.Name("irrelevant name")
-            cancellable = center.notifications(named: name).map(\.name)
+            cancellable = center.notifications(named: name)
+                .map(\.name)
                 .monitor(context: self) { _, _ in }
         }
 
@@ -73,7 +80,8 @@ class AsyncMonitorTests {
 
     @Test func stopsCallingBlockWhenContextIsDeallocated() async throws {
         var context: NSObject? = NSObject()
-        subject = center.notifications(named: name).map(\.name)
+        subject = center.notifications(named: name)
+            .map(\.name)
             .monitor(context: context!) { context, receivedName in
                 Issue.record("Called after context was deallocated")
             }
@@ -83,4 +91,21 @@ class AsyncMonitorTests {
         }
         try await Task.sleep(for: .milliseconds(10))
     }
+
+    @Test func equatable() throws {
+        let subject = AsyncMonitor(sequence: AsyncStream.just(42)) { _ in }
+        #expect(subject == subject)
+        #expect(subject != AsyncMonitor(sequence: AsyncStream.just(42)) { _ in })
+    }
+
+    @Test func hashable() throws {
+        let subjects = (1...100).map { _ in
+            AsyncMonitor(sequence: AsyncStream.just(42)) { _ in }
+        }
+        var hashValues: Set<Int> = []
+        for subject in subjects {
+            hashValues.insert(subject.hashValue)
+        }
+        #expect(hashValues.count == subjects.count)
+    }
 }

Tests/AsyncMonitorTests/AsyncSequence+Just.swift

@@ -0,0 +1,9 @@
+import Foundation
+
+extension AsyncSequence where Element: Sendable {
+    static func just(_ value: Element) -> AsyncStream<Element> {
+        AsyncStream { continuation in
+            continuation.yield(value)
+        }
+    }
+}

Tests/AsyncMonitorTests/NSObject+AsyncKVOTests.swift

@@ -0,0 +1,21 @@
+@testable import AsyncMonitor
+import Foundation
+import Testing
+
+class AsyncKVOTests {
+    var subject: Progress? = Progress(totalUnitCount: 42)
+    var cancellable: (any AsyncCancellable)?
+
+    @Test func yieldsChanges() async throws {
+        let subject = try #require(subject)
+        var values = [Double]()
+        cancellable = subject.values(for: \.fractionCompleted) { progress in
+            values.append(progress)
+        }
+        for _ in 1...3 {
+            subject.completedUnitCount += 1
+            await Task.yield()
+        }
+        #expect(values.count == 3)
+    }
+}

Tests/AsyncMonitorTests/ReadmeExamples.swift

@@ -1,9 +1,12 @@
 import Foundation
 @testable import AsyncMonitor
 
+// MARK: Basics
+
 class SimplestVersion {
     let cancellable = NotificationCenter.default
-        .notifications(named: .NSCalendarDayChanged).map(\.name)
+        .notifications(named: .NSCalendarDayChanged)
+        .map(\.name)
         .monitor { _ in
             print("The date is now \(Date.now)")
         }
@@ -14,7 +17,8 @@ class WithContext {
 
     init() {
         NotificationCenter.default
-            .notifications(named: .NSCalendarDayChanged).map(\.name)
+            .notifications(named: .NSCalendarDayChanged)
+            .map(\.name)
             .monitor(context: self) { _self, _ in
                 _self.dayChanged()
             }.store(in: &cancellables)
@@ -24,3 +28,34 @@ class WithContext {
         print("The date is now \(Date.now)")
     }
 }
+
+// MARK: - Combine
+
+import Combine
+
+class CombineExample {
+    var cancellables = Set<AnyAsyncCancellable>()
+
+    init() {
+        Timer.publish(every: 1.0, on: .main, in: .common)
+            .autoconnect()
+            .values
+            .monitor { date in
+                print("Timer fired at \(date)")
+            }
+            .store(in: &cancellables)
+    }
+}
+
+// MARK: - KVO
+
+class KVOExample {
+    var cancellables = Set<AnyAsyncCancellable>()
+
+    init() {
+        let progress = Progress(totalUnitCount: 42)
+        progress.values(for: \.fractionCompleted) { fraction in
+            print("Progress is \(fraction.formatted(.percent))%")
+        }.store(in: &cancellables)
+    }
+}

Tests/AsyncMonitorTests/TestCancellable.swift

@@ -0,0 +1,20 @@
+import AsyncMonitor
+
+class TestCancellable: AsyncCancellable {
+    lazy var id = ObjectIdentifier(self)
+    var isCancelled = false
+
+    func cancel() {
+        isCancelled = true
+    }
+
+    // MARK: Hashable conformance
+
+    public static func == (lhs: TestCancellable, rhs: TestCancellable) -> Bool {
+        lhs.id == rhs.id
+    }
+
+    public func hash(into hasher: inout Hasher) {
+        hasher.combine(id)
+    }
+}