Solution using presents

Demo.xcodeproj/project.pbxproj

@@ -11,9 +11,11 @@
 		3136F93A24B4D0D400A17C89 /* SceneDelegate.swift in Sources */ = {isa = PBXBuildFile; fileRef = 3136F93924B4D0D400A17C89 /* SceneDelegate.swift */; };
 		3136F93C24B4D0D400A17C89 /* App.swift in Sources */ = {isa = PBXBuildFile; fileRef = 3136F93B24B4D0D400A17C89 /* App.swift */; };
 		3136F93E24B4D0D600A17C89 /* Assets.xcassets in Resources */ = {isa = PBXBuildFile; fileRef = 3136F93D24B4D0D600A17C89 /* Assets.xcassets */; };
-		3136F94424B4D0D600A17C89 /* LaunchScreen.storyboard in Resources */ = {isa = PBXBuildFile; fileRef = 3136F94224B4D0D600A17C89 /* LaunchScreen.storyboard */; };
 		3136F94D24B4D25F00A17C89 /* ComposableArchitecture in Frameworks */ = {isa = PBXBuildFile; productRef = 3136F94C24B4D25F00A17C89 /* ComposableArchitecture */; };
+		31CBF90424B5143500968607 /* Lifecycle.swift in Sources */ = {isa = PBXBuildFile; fileRef = 31CBF90324B5143500968607 /* Lifecycle.swift */; };
 		31F1C4F124B4D3CC0028825C /* Detail.swift in Sources */ = {isa = PBXBuildFile; fileRef = 31F1C4F024B4D3CC0028825C /* Detail.swift */; };
+		A3458DDB257F759A00C909BB /* Avatar.swift in Sources */ = {isa = PBXBuildFile; fileRef = A3458DDA257F759A00C909BB /* Avatar.swift */; };
+		A362BEE025A753D600B183C9 /* Cancellation.swift in Sources */ = {isa = PBXBuildFile; fileRef = A362BEDF25A753D600B183C9 /* Cancellation.swift */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXFileReference section */
@@ -22,9 +24,11 @@
 		3136F93924B4D0D400A17C89 /* SceneDelegate.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SceneDelegate.swift; sourceTree = "<group>"; };
 		3136F93B24B4D0D400A17C89 /* App.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = App.swift; sourceTree = "<group>"; };
 		3136F93D24B4D0D600A17C89 /* Assets.xcassets */ = {isa = PBXFileReference; lastKnownFileType = folder.assetcatalog; path = Assets.xcassets; sourceTree = "<group>"; };
-		3136F94324B4D0D600A17C89 /* Base */ = {isa = PBXFileReference; lastKnownFileType = file.storyboard; name = Base; path = Base.lproj/LaunchScreen.storyboard; sourceTree = "<group>"; };
 		3136F94524B4D0D600A17C89 /* Info.plist */ = {isa = PBXFileReference; lastKnownFileType = text.plist.xml; path = Info.plist; sourceTree = "<group>"; };
+		31CBF90324B5143500968607 /* Lifecycle.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Lifecycle.swift; sourceTree = "<group>"; };
 		31F1C4F024B4D3CC0028825C /* Detail.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Detail.swift; sourceTree = "<group>"; };
+		A3458DDA257F759A00C909BB /* Avatar.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Avatar.swift; sourceTree = "<group>"; };
+		A362BEDF25A753D600B183C9 /* Cancellation.swift */ = {isa = PBXFileReference; indentWidth = 2; lastKnownFileType = sourcecode.swift; path = Cancellation.swift; sourceTree = "<group>"; tabWidth = 2; };
 /* End PBXFileReference section */
 
 /* Begin PBXFrameworksBuildPhase section */
@@ -62,9 +66,11 @@
 				3136F93724B4D0D400A17C89 /* AppDelegate.swift */,
 				3136F93D24B4D0D600A17C89 /* Assets.xcassets */,
 				31F1C4F024B4D3CC0028825C /* Detail.swift */,
+				A3458DDA257F759A00C909BB /* Avatar.swift */,
 				3136F94524B4D0D600A17C89 /* Info.plist */,
-				3136F94224B4D0D600A17C89 /* LaunchScreen.storyboard */,
+				31CBF90324B5143500968607 /* Lifecycle.swift */,
 				3136F93924B4D0D400A17C89 /* SceneDelegate.swift */,
+				A362BEDF25A753D600B183C9 /* Cancellation.swift */,
 			);
 			path = Demo;
 			sourceTree = "<group>";
@@ -133,7 +139,6 @@
 			isa = PBXResourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
-				3136F94424B4D0D600A17C89 /* LaunchScreen.storyboard in Resources */,
 				3136F93E24B4D0D600A17C89 /* Assets.xcassets in Resources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
@@ -145,26 +150,18 @@
 			isa = PBXSourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				A3458DDB257F759A00C909BB /* Avatar.swift in Sources */,
 				3136F93824B4D0D400A17C89 /* AppDelegate.swift in Sources */,
 				3136F93A24B4D0D400A17C89 /* SceneDelegate.swift in Sources */,
 				31F1C4F124B4D3CC0028825C /* Detail.swift in Sources */,
+				31CBF90424B5143500968607 /* Lifecycle.swift in Sources */,
 				3136F93C24B4D0D400A17C89 /* App.swift in Sources */,
+				A362BEE025A753D600B183C9 /* Cancellation.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
 /* End PBXSourcesBuildPhase section */
 
-/* Begin PBXVariantGroup section */
-		3136F94224B4D0D600A17C89 /* LaunchScreen.storyboard */ = {
-			isa = PBXVariantGroup;
-			children = (
-				3136F94324B4D0D600A17C89 /* Base */,
-			);
-			name = LaunchScreen.storyboard;
-			sourceTree = "<group>";
-		};
-/* End PBXVariantGroup section */
-
 /* Begin XCBuildConfiguration section */
 		3136F94624B4D0D600A17C89 /* Debug */ = {
 			isa = XCBuildConfiguration;

Demo/App.swift

@@ -2,36 +2,59 @@ import ComposableArchitecture
 import SwiftUI
 
 struct AppState: Equatable {
-    var detail: DetailState?
+    var detail1: DetailState?
+    var detail2: DetailState? = DetailState()
 }
 
 enum AppAction {
-    case presentDetail
-    case dismissDetail
-    case detail(DetailAction)
+    case presentDetail1
+    case dismissDetail1
+    case detail1(DetailAction)
+    case detail2(DetailAction)
 }
 
-let appReducer = Reducer<AppState, AppAction, Void>.combine(
-    detailReducer.optional.pullback(
-        state: \.detail,
-        action: /AppAction.detail,
-        environment: { _ in () }
-    ),
-    Reducer { state, action, _ in
+struct AppEnvironment {
+    let cancellationId: AnyHashable
+}
+
+let appReducer = Reducer<AppState, AppAction, AppEnvironment>.combine(
+    Reducer { state, action, env in
         switch action {
-        case .presentDetail:
-            state.detail = .init()
+        case .presentDetail1:
+            state.detail1 = .init()
             return .none
 
-        case .dismissDetail:
-            state.detail = nil
-
+        case .dismissDetail1:
+            state.detail1 = nil
+            return .none
+
+        case .detail1(.onDisappear):
+            state.detail1 = nil
             return .none
 
-        case .detail(_):
+        case .detail1(_):
+            return .none
+
+        case .detail2(_):
             return .none
         }
-    }
+    }.presents(
+        detailReducer,
+        cancelEffectsOnDismiss: true,
+        state: \.detail1,
+        action: /AppAction.detail1,
+        environment: { env in
+            DetailEnvironment(cancellationId: [env.cancellationId, 1])
+        }
+    ).presents(
+        detailReducer,
+        cancelEffectsOnDismiss: true,
+        state: \.detail2,
+        action: /AppAction.detail2,
+        environment: { env in
+            DetailEnvironment(cancellationId: [env.cancellationId, 2])
+        }
+    )
 )
 
 struct AppView: View {
@@ -41,21 +64,30 @@ struct AppView: View {
         WithViewStore(store) { viewStore in
             VStack(spacing: 16) {
                 Text("App").font(.title).padding(.top, 100)
-                if viewStore.state.detail != nil {
-                    Button(action: { viewStore.send(.dismissDetail) }) {
+                if viewStore.state.detail1 != nil {
+                    Button(action: { viewStore.send(.dismissDetail1) }) {
                         Text("Dismiss Detail")
                     }
                 } else {
-                    Button(action: { viewStore.send(.presentDetail) }) {
+                    Button(action: { viewStore.send(.presentDetail1) }) {
                         Text("Present Detail")
                     }
                 }
+
+                IfLetStore(self.store.scope(
+                    state: \.detail1,
+                    action: AppAction.detail1
+                )) { detailStore in
+                    DetailView(store: detailStore)
+                }
+
                 IfLetStore(self.store.scope(
-                    state: \.detail,
-                    action: AppAction.detail
+                    state: \.detail2,
+                    action: AppAction.detail2
                 )) { detailStore in
                     DetailView(store: detailStore)
                 }
+
                 Spacer()
             }
         }

Demo/Avatar.swift

@@ -0,0 +1,98 @@
+import ComposableArchitecture
+import Combine
+import SwiftUI
+
+struct AvatarState: Equatable {
+    var image: UIImage?
+    var error: AvatarError?
+}
+
+enum AvatarAction: Equatable {
+    case onAppear
+    case onDisappear
+    case load
+    case loaded(String)
+    case failed(AvatarError)
+}
+
+enum AvatarError: Error, Equatable {
+    case network
+}
+
+struct AvatarEnvironment {
+    var cancellationId: AnyHashable
+}
+
+let avatarReducer = Reducer<AvatarState, AvatarAction, AvatarEnvironment> { state, action, env in
+
+    switch action {
+
+    case .load:
+        return Just("faceid")
+            .map { AvatarAction.loaded($0) }
+            .replaceError(with: AvatarAction.failed(.network))
+            .delay(for: .seconds(1), scheduler: DispatchQueue.main)
+            .handleEvents(receiveSubscription: { (sub) in
+                print("receiveSubscription avatar")
+            }, receiveOutput: { (output) in
+                print("receiveOutput avatar")
+            }, receiveCompletion: { (completion) in
+                print("receiveCompletion avatar")
+            }, receiveCancel: {
+                print("receiveCancel avatar")
+            }, receiveRequest: { (demand) in
+                print("receiveRequest avatar")
+            })
+            .eraseToEffect()
+            .cancellable(id: env.cancellationId)
+
+    case .loaded(let name):
+        state.image = UIImage(systemName: name)
+        return .none
+
+    case .failed(let error):
+        state.error = error
+        return .none
+
+    case .onAppear:
+        return .init(value: .load)
+
+    case .onDisappear:
+        return .cancel(id: env.cancellationId)
+    }
+}
+
+struct AvatarView: View {
+    var store: Store<AvatarState, AvatarAction>
+
+    var body: some View {
+        WithViewStore(store) { viewStore in
+            VStack(spacing: 16) {
+                if let _ = viewStore.error {
+                    Image(systemName: "person.crop.circle.badge.xmark")
+                } else if let image = viewStore.image {
+                    Image(uiImage: image)
+                } else {
+                    Image(systemName: "clock")
+                }
+            }.onAppear {
+                viewStore.send(.onAppear)
+            }
+            .onDisappear {
+                viewStore.send(.onDisappear)
+            }
+        }
+    }
+}
+
+#if DEBUG
+struct AvatarView_Previews: PreviewProvider {
+    static var previews: some View {
+        DetailView(store: Store(
+            initialState: .init(),
+            reducer: .empty,
+            environment: ()
+        ))
+    }
+}
+#endif

Demo/Cancellation.swift

@@ -0,0 +1,44 @@
+import ComposableArchitecture
+
+extension Reducer {
+
+  fileprivate func nonCrashingOptional(_ file: StaticString = #file, _ line: UInt = #line) -> Reducer<
+    State?, Action, Environment
+  > {
+    .init { state, action, environment in
+      guard state != nil else {
+        return .none
+      }
+      return self.run(&state!, action, environment)
+    }
+  }
+
+  public func presents<LocalState, LocalAction, LocalEnvironment>(
+    _ localReducer: Reducer<LocalState, LocalAction, LocalEnvironment>,
+    cancelEffectsOnDismiss: Bool,
+    state toLocalState: WritableKeyPath<State, LocalState?>,
+    action toLocalAction: CasePath<Action, LocalAction>,
+    environment toLocalEnvironment: @escaping (Environment) -> LocalEnvironment
+  ) -> Self {
+    let id = UUID()
+    return Self { state, action, environment in
+      let hadLocalState = state[keyPath: toLocalState] != nil
+      let localEffects = localReducer
+        .nonCrashingOptional()
+        .pullback(state: toLocalState, action: toLocalAction, environment: toLocalEnvironment)
+        .run(&state, action, environment)
+        .cancellable(id: id)
+      let globalEffects = self.run(&state, action, environment)
+      let hasLocalState = state[keyPath: toLocalState] != nil
+      print("Presents with cancellation id \(id)")
+      if cancelEffectsOnDismiss && hadLocalState && !hasLocalState {
+        print("Cancels cancellation id \(id)")
+      }
+      return .merge(
+        localEffects,
+        globalEffects,
+        cancelEffectsOnDismiss && hadLocalState && !hasLocalState ? .cancel(id: id) : .none
+      )
+    }
+  }
+}