Implementation for ObservableObject with Mirror

Package.swift

@@ -23,15 +23,13 @@ let package = Package(
         .library(name: "OpenCombineDispatch", targets: ["OpenCombineDispatch"]),
         .library(name: "OpenCombineFoundation", targets: ["OpenCombineFoundation"]),
     ],
-    dependencies: [.package(url: "https://github.com/MaxDesiatov/Runtime.git", from: "2.1.2")],
     targets: [
         .target(name: "COpenCombineHelpers"),
         .target(
             name: "OpenCombine",
             dependencies: [
                 .target(name: "COpenCombineHelpers",
-                        condition: .when(platforms: supportedPlatforms.except([.wasi]))),
-                .product(name: "Runtime", package: "Runtime", condition: .when(platforms: [.wasi])),
+                        condition: .when(platforms: supportedPlatforms.except([.wasi])))
             ],
             exclude: [
                 "Publishers/Publishers.Encode.swift.gyb",

README.md

@@ -24,9 +24,14 @@ dependencies: [
     .package(url: "https://github.com/OpenCombine/OpenCombine.git", from: "0.11.0")
 ],
 targets: [
-    .target(name: "MyAwesomePackage", dependencies: ["OpenCombine",
-                                                     "OpenCombineDispatch",
-                                                     "OpenCombineFoundation"])
+    .target(
+        name: "MyAwesomePackage",
+        dependencies: [
+            "OpenCombine",
+            .product(name: "OpenCombineFoundation", package: "OpenCombine"),
+            .product(name: "OpenCombineDispatch", package: "OpenCombine")
+        ]
+    ),
 ]
 ```
 

Sources/OpenCombine/ObservableObject.swift

@@ -5,10 +5,6 @@
 //  Created by Sergej Jaskiewicz on 08/09/2019.
 //
 
-#if canImport(Runtime)
-import Runtime
-#endif
-
 /// A type of object with a publisher that emits before the object has changed.
 ///
 /// By default an `ObservableObject` synthesizes an `objectWillChange` publisher that
@@ -46,103 +42,58 @@ public protocol ObservableObject: AnyObject {
     var objectWillChange: ObjectWillChangePublisher { get }
 }
 
-#if swift(>=5.1) && canImport(Runtime)
 private protocol _ObservableObjectProperty {
-    var objectWillChange: ObservableObjectPublisher? { get set }
-}
-
-extension _ObservableObjectProperty {
-
-    fileprivate static func installPublisher(
-        _ publisher: ObservableObjectPublisher,
-        on publishedStorage: UnsafeMutableRawPointer
-    ) {
-        // It is safe to call assumingMemoryBound here because we know for sure
-        // that the actual type of the pointee is Self.
-        publishedStorage
-            .assumingMemoryBound(to: Self.self)
-            .pointee
-            .objectWillChange = publisher
-    }
-
-    fileprivate static func getPublisher(
-        from publishedStorage: UnsafeMutableRawPointer
-    ) -> ObservableObjectPublisher? {
-        // It is safe to call assumingMemoryBound here because we know for sure
-        // that the actual type of the pointee is Self.
-        return publishedStorage
-            .assumingMemoryBound(to: Self.self)
-            .pointee
-            .objectWillChange
-    }
+    var objectWillChange: ObservableObjectPublisher? { get nonmutating set }
 }
 
+#if swift(>=5.1)
 extension Published: _ObservableObjectProperty {}
-#endif
 
 extension ObservableObject where ObjectWillChangePublisher == ObservableObjectPublisher {
-    // swiftlint:disable let_var_whitespace
-#if swift(>=5.1)
+
     /// A publisher that emits before the object has changed.
-    #if canImport(Runtime)
     public var objectWillChange: ObservableObjectPublisher {
         var installedPublisher: ObservableObjectPublisher?
-        let info = try! typeInfo(of: Self.self)
-        for property in info.properties {
-            let storage = Unmanaged
-                .passUnretained(self)
-                .toOpaque()
-                .advanced(by: property.offset)
-
-            guard let fieldType = property.type as? _ObservableObjectProperty.Type else {
-                // Visit other fields until we meet a @Published field
-                continue
-            }
+        var reflection: Mirror? = Mirror(reflecting: self)
+        while let aClass = reflection {
+            for (_, property) in aClass.children {
+                guard let property = property as? _ObservableObjectProperty else {
+                    // Visit other fields until we meet a @Published field
+                    continue
+                }
 
-            // Now we know that the field is @Published.
-            if let alreadyInstalledPublisher = fieldType.getPublisher(from: storage) {
-                installedPublisher = alreadyInstalledPublisher
-                // Don't visit other fields, as all @Published fields
-                // already have a publisher installed.
-                break
-            }
+                // Now we know that the field is @Published.
+                if let alreadyInstalledPublisher = property.objectWillChange {
+                    installedPublisher = alreadyInstalledPublisher
+                    // Don't visit other fields, as all @Published fields
+                    // already have a publisher installed.
+                    break
+                }
 
-            // Okay, this field doesn't have a publisher installed.
-            // This means that other fields don't have it either
-            // (because we install it only once and fields can't be added at runtime).
-            var lazilyCreatedPublisher: ObjectWillChangePublisher {
-                if let publisher = installedPublisher {
+                // Okay, this field doesn't have a publisher installed.
+                // This means that other fields don't have it either
+                // (because we install it only once and fields can't be added at runtime).
+                var lazilyCreatedPublisher: ObjectWillChangePublisher {
+                    if let publisher = installedPublisher {
+                        return publisher
+                    }
+                    let publisher = ObservableObjectPublisher()
+                    installedPublisher = publisher
                     return publisher
                 }
-                let publisher = ObservableObjectPublisher()
-                installedPublisher = publisher
-                return publisher
-            }
 
-            fieldType.installPublisher(lazilyCreatedPublisher, on: storage)
+                property.objectWillChange = lazilyCreatedPublisher
 
-            // Continue visiting other fields.
+                // Continue visiting other fields.
+            }
+            reflection = aClass.superclassMirror
         }
         return installedPublisher ?? ObservableObjectPublisher()
     }
-    #else
-    @available(*, unavailable, message: """
-               The default implementation of objectWillChange is not available yet. \
-               It's being worked on in \
-               https://github.com/broadwaylamb/OpenCombine/pull/97
-               """)
-    public var objectWillChange: ObservableObjectPublisher {
-        fatalError("unimplemented")
-    }
-    #endif
-#else
-    public var objectWillChange: ObservableObjectPublisher {
-        return ObservableObjectPublisher()
-    }
-#endif
-    // swiftlint:enable let_var_whitespace
 }
 
+#endif
+
 /// A publisher that publishes changes from observable objects.
 public final class ObservableObjectPublisher: Publisher {
 

Sources/OpenCombine/Published.swift

@@ -107,8 +107,16 @@ public struct Published<Value> {
         case value(Value)
         case publisher(Publisher)
     }
+    @propertyWrapper
+    private class Box {
+        var wrappedValue: Storage
 
-    private var storage: Storage
+        init(wrappedValue: Storage) {
+            self.wrappedValue = wrappedValue
+        }
+    }
+
+    @Box private var storage: Storage
 
     internal var objectWillChange: ObservableObjectPublisher? {
         get {
@@ -119,7 +127,7 @@ public struct Published<Value> {
                 return publisher.subject.objectWillChange
             }
         }
-        set {
+        nonmutating set {
             projectedValue.subject.objectWillChange = newValue
         }
     }
@@ -145,14 +153,14 @@ public struct Published<Value> {
     ///
     /// - Parameter initialValue: The publisher's initial value.
     public init(wrappedValue: Value) {
-        storage = .value(wrappedValue)
+        _storage = Box(wrappedValue: .value(wrappedValue))
     }
 
     /// The property for which this instance exposes a publisher.
     ///
     /// The `projectedValue` is the property accessed with the `$` operator.
     public var projectedValue: Publisher {
-        mutating get {
+        get {
             switch storage {
             case .value(let value):
                 let publisher = Publisher(value)

Sources/OpenCombine/Publishers/Publishers.FlatMap.swift

@@ -157,17 +157,17 @@ extension Publishers {
         public func receive<Downstream: Subscriber>(subscriber: Downstream)
             where Child.Output == Downstream.Input, Upstream.Failure == Downstream.Failure
         {
-            let inner = Inner(downstream: subscriber,
+            let outer = Outer(downstream: subscriber,
                               maxPublishers: maxPublishers,
                               map: transform)
-            subscriber.receive(subscription: inner)
-            upstream.subscribe(inner)
+            subscriber.receive(subscription: outer)
+            upstream.subscribe(outer)
         }
     }
 }
 
 extension Publishers.FlatMap {
-    private final class Inner<Downstream: Subscriber>
+    private final class Outer<Downstream: Subscriber>
         : Subscriber,
           Subscription,
           CustomStringConvertible,
@@ -243,7 +243,7 @@ extension Publishers.FlatMap {
             subscription.request(maxPublishers)
         }
 
-        fileprivate func receive(_ input: Upstream.Output) -> Subscribers.Demand {
+        fileprivate func receive(_ input: Input) -> Subscribers.Demand {
             lock.lock()
             let cancelledOrCompleted = self.cancelledOrCompleted
             lock.unlock()
@@ -260,9 +260,9 @@ extension Publishers.FlatMap {
             return .none
         }
 
-        fileprivate func receive(completion: Subscribers.Completion<Child.Failure>) {
-            outerSubscription = nil
+        fileprivate func receive(completion: Subscribers.Completion<Failure>) {
             lock.lock()
+            outerSubscription = nil
             outerFinished = true
             switch completion {
             case .finished:
@@ -272,6 +272,8 @@ extension Publishers.FlatMap {
                 let wasAlreadyCancelledOrCompleted = cancelledOrCompleted
                 cancelledOrCompleted = true
                 for (_, subscription) in subscriptions {
+                    // Cancelling subscriptions with the lock acquired. Not good,
+                    // but that's what Combine does. This code path is tested.
                     subscription.cancel()
                 }
                 subscriptions = [:]
@@ -354,16 +356,21 @@ extension Publishers.FlatMap {
 
         fileprivate func cancel() {
             lock.lock()
+            if cancelledOrCompleted {
+                lock.unlock()
+                return
+            }
             cancelledOrCompleted = true
             let subscriptions = self.subscriptions
             self.subscriptions = [:]
+            let outerSubscription = self.outerSubscription
+            self.outerSubscription = nil
             lock.unlock()
             for (_, subscription) in subscriptions {
                 subscription.cancel()
             }
-            // Combine doesn't acquire the lock here. Weird.
+            // Combine doesn't acquire outerLock here. Weird.
             outerSubscription?.cancel()
-            outerSubscription = nil
         }
 
         // MARK: - Reflection
@@ -471,9 +478,9 @@ extension Publishers.FlatMap {
         private func releaseLockThenSendCompletionDownstreamIfNeeded(
             outerFinished: Bool
         ) -> Bool {
-            #if DEBUG
+#if DEBUG
             lock.assertOwner() // Sanity check
-            #endif
+#endif
             if !cancelledOrCompleted && outerFinished && buffer.isEmpty &&
                 subscriptions.count + pendingSubscriptions == 0 {
                 cancelledOrCompleted = true
@@ -495,10 +502,10 @@ extension Publishers.FlatMap {
                              CustomReflectable,
                              CustomPlaygroundDisplayConvertible {
             private let index: SubscriptionIndex
-            private let inner: Inner
+            private let inner: Outer
             fileprivate let combineIdentifier = CombineIdentifier()
 
-            fileprivate init(index: SubscriptionIndex, inner: Inner) {
+            fileprivate init(index: SubscriptionIndex, inner: Outer) {
                 self.index = index
                 self.inner = inner
             }

Tests/OpenCombineTests/Helpers/AssertCrashes.swift

@@ -84,4 +84,13 @@ extension XCTest {
         }
 #endif // !Xcode && !os(iOS) && !os(watchOS) && !os(tvOS) && !WASI
     }
+
+    @available(macOS 10.13, iOS 8.0, *)
+    func assertCrashesOnDarwin(within body: () -> Void) {
+#if canImport(Darwin) && OPENCOMBINE_COMPATIBILITY_TEST
+        assertCrashes(within: body)
+#else
+        body()
+#endif
+    }
 }