[RFC] [DNM] SideEffect as Type

swift/Samples/SampleApp/Sources/DemoWorkflow.swift

@@ -30,7 +30,6 @@ struct DemoWorkflow: Workflow {
 
 extension DemoWorkflow {
     struct State {
-        fileprivate var signal: TimerSignal
         var colorState: ColorState
         var loadingState: LoadingState
         var subscriptionState: SubscriptionState
@@ -54,7 +53,6 @@ extension DemoWorkflow {
 
     func makeInitialState() -> DemoWorkflow.State {
         return State(
-            signal: TimerSignal(),
             colorState: .red,
             loadingState: .idle(title: "Not Loaded"),
             subscriptionState: .not
@@ -172,10 +170,16 @@ extension DemoWorkflow {
         case .not:
             subscribeTitle = "Subscribe"
         case .subscribing:
-            // Subscribe to the timer signal, simulating the title being tapped.
-            context.awaitResult(for: state.signal.signal.asWorker(key: "Timer")) { _ -> Action in
-                .titleButtonTapped
+            context.run(SideEffectPerformer<Action>(key: "Timer") { sink, lifetime in
+                let timer = Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { timer in
+                    sink.send(.titleButtonTapped)
+                }
+
+                lifetime.onEnded {
+                    timer.invalidate()
+                }
             }
+            )
             subscribeTitle = "Stop"
         }
 
@@ -200,21 +204,3 @@ extension DemoWorkflow {
         )
     }
 }
-
-private class TimerSignal {
-    let signal: Signal<Void, Never>
-    let observer: Signal<Void, Never>.Observer
-    let timer: Timer
-
-    init() {
-        let (signal, observer) = Signal<Void, Never>.pipe()
-
-        let timer = Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { [weak observer] _ in
-            observer?.send(value: ())
-        }
-
-        self.signal = signal
-        self.observer = observer
-        self.timer = timer
-    }
-}

swift/Samples/TicTacToe/Sources/Authentication/AuthenticationWorkflow.swift

@@ -218,15 +218,17 @@ extension AuthenticationWorkflow {
                     authenticationService: authenticationService,
                     intermediateToken: intermediateSession,
                     twoFactorCode: twoFactorCode
-                ))
+                )
+            )
 
             backStackItems.append(twoFactorScreen(error: nil, intermediateSession: intermediateSession, sink: sink))
             modals.append(ModalContainerScreenModal(screen: AnyScreen(LoadingScreen()), style: .fullScreen, key: "", animated: false))
         }
         return AlertContainerScreen(
             baseScreen: ModalContainerScreen(
                 baseScreen: BackStackScreen(
-                    items: backStackItems),
+                    items: backStackItems
+                ),
                 modals: modals
             ),
             alert: alert
@@ -259,7 +261,8 @@ extension AuthenticationWorkflow {
                     handler: {
                         sink.send(.back)
                     }
-                ))))
+                ))
+            ))
         )
     }
 }

swift/Workflow/Sources/Lifetime.swift

@@ -17,6 +17,10 @@
 import Foundation
 
 public final class Lifetime {
+    public init(action: @escaping () -> Void) {
+        onEnded(action)
+    }
+
     public func onEnded(_ action: @escaping () -> Void) {
         assert(!hasEnded, "Lifetime used after being ended.")
         onEndedActions.append(action)

swift/Workflow/Sources/RenderContext.swift

@@ -75,7 +75,7 @@ public class RenderContext<WorkflowType: Workflow>: RenderContextType {
         fatalError()
     }
 
-    public func runSideEffect(key: AnyHashable, action: (Lifetime) -> Void) {
+    public func run<S: SideEffect>(_ sideEffect: S) {
         fatalError()
     }
 
@@ -107,9 +107,9 @@ public class RenderContext<WorkflowType: Workflow>: RenderContextType {
             return implementation.makeSink(of: actionType)
         }
 
-        override func runSideEffect(key: AnyHashable, action: (_ lifetime: Lifetime) -> Void) {
+        override func run<S: SideEffect>(_ sideEffect: S) where S.Action.WorkflowType == WorkflowType {
             assertStillValid()
-            implementation.runSideEffect(key: key, action: action)
+            implementation.run(sideEffect)
         }
 
         override func awaitResult<W, Action>(for worker: W, outputMap: @escaping (W.Output) -> Action) where W: Worker, Action: WorkflowAction, WorkflowType == Action.WorkflowType {
@@ -132,7 +132,7 @@ internal protocol RenderContextType: AnyObject {
 
     func awaitResult<W, Action>(for worker: W, outputMap: @escaping (W.Output) -> Action) where W: Worker, Action: WorkflowAction, Action.WorkflowType == WorkflowType
 
-    func runSideEffect(key: AnyHashable, action: (_ lifetime: Lifetime) -> Void)
+    func run<S: SideEffect>(_ sideEffect: S) where S.Action.WorkflowType == WorkflowType
 }
 
 extension RenderContext {

swift/Workflow/Sources/SideEffect.swift

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2020 Square Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+public protocol SideEffect: Hashable {
+    associatedtype Action: WorkflowAction
+
+    func run(sink: Sink<Action>) -> Lifetime
+}

swift/Workflow/Sources/SideEffectPerformer.swift

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2020 Square Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import Foundation
+
+public struct SideEffectPerformer<Action: WorkflowAction>: SideEffect {
+    let key: AnyHashable
+    let action: (Sink<Action>, Lifetime) -> Void
+
+    public init(key: AnyHashable, action: @escaping (Sink<Action>, Lifetime) -> Void) {
+        self.key = key
+        self.action = action
+    }
+
+    public func run(sink: Sink<Action>) -> Lifetime {
+        let lifetime = Lifetime {}
+        action(sink, lifetime)
+        return lifetime
+    }
+
+    public static func == (lhs: SideEffectPerformer, rhs: SideEffectPerformer) -> Bool {
+        lhs.key == rhs.key
+    }
+
+    public func hash(into hasher: inout Hasher) {
+        hasher.combine(key)
+    }
+}

swift/Workflow/Sources/SubtreeManager.swift

@@ -247,13 +247,13 @@ extension WorkflowNode.SubtreeManager {
             }
         }
 
-        func runSideEffect(key: AnyHashable, action: (Lifetime) -> Void) {
-            if let existingSideEffect = originalSideEffectLifetimes[key] {
-                usedSideEffectLifetimes[key] = existingSideEffect
+        func run<S: SideEffect>(_ sideEffect: S) where S.Action.WorkflowType == WorkflowType {
+            let sink = makeSink(of: S.Action.self)
+            if let existingSideEffect = originalSideEffectLifetimes[sideEffect] {
+                usedSideEffectLifetimes[sideEffect] = existingSideEffect
             } else {
-                let sideEffectLifetime = SideEffectLifetime()
-                action(sideEffectLifetime.lifetime)
-                usedSideEffectLifetimes[key] = sideEffectLifetime
+                let lifetime = sideEffect.run(sink: sink)
+                usedSideEffectLifetimes[sideEffect] = SideEffectLifetime(lifetime: lifetime)
             }
         }
     }
@@ -553,7 +553,11 @@ extension WorkflowNode.SubtreeManager {
         fileprivate let lifetime: Lifetime
 
         fileprivate init() {
-            self.lifetime = Lifetime()
+            self.lifetime = Lifetime {}
+        }
+
+        fileprivate init(lifetime: Lifetime) {
+            self.lifetime = lifetime
         }
 
         deinit {

swift/Workflow/Tests/SubtreeManagerTests.swift

@@ -15,6 +15,7 @@
  */
 
 import ReactiveSwift
+import class Workflow.Lifetime
 import XCTest
 @testable import Workflow
 
@@ -304,7 +305,7 @@ final class SubtreeManagerTests: XCTestCase {
         XCTAssertTrue(manager.sideEffectLifetimes.isEmpty)
 
         _ = manager.render { context -> TestViewModel in
-            context.runSideEffect(key: "helloWorld") { _ in }
+            context.run(TestSideEffect(lifetime: Lifetime()))
             return context.render(
                 workflow: TestWorkflow(),
                 key: "",
@@ -316,7 +317,7 @@ final class SubtreeManagerTests: XCTestCase {
         let sideEffectKey = manager.sideEffectLifetimes.values.first!
 
         _ = manager.render { context -> TestViewModel in
-            context.runSideEffect(key: "helloWorld") { _ in }
+            context.run(TestSideEffect(lifetime: Lifetime()))
             return context.render(
                 workflow: TestWorkflow(),
                 key: "",
@@ -334,13 +335,13 @@ final class SubtreeManagerTests: XCTestCase {
 
         let lifetimeEndedExpectation = expectation(description: "Lifetime Ended Expectations")
         _ = manager.render { context -> TestViewModel in
-            context.runSideEffect(key: "helloWorld") { lifetime in
-                lifetime.onEnded {
-                    // Capturing `lifetime` to make sure a retain-cycle will still trigger the `onEnded` block
-                    print("\(lifetime)")
-                    lifetimeEndedExpectation.fulfill()
-                }
+            let lifetime = Lifetime()
+            lifetime.onEnded {
+                // Capturing `lifetime` to make sure a retain-cycle will still trigger the `onEnded` block
+                print("\(lifetime)")
+                lifetimeEndedExpectation.fulfill()
             }
+            context.run(TestSideEffect(lifetime: lifetime))
             return context.render(
                 workflow: TestWorkflow(),
                 key: "",
@@ -363,6 +364,20 @@ final class SubtreeManagerTests: XCTestCase {
     }
 }
 
+private struct TestSideEffect: SideEffect, Hashable {
+    let key: String = "Test Side Effect"
+    let lifetime: Lifetime
+    func run() -> Lifetime {
+        lifetime
+    }
+
+    static func == (lhs: TestSideEffect, rhs: TestSideEffect) -> Bool {
+        true
+    }
+
+    func hash(into hasher: inout Hasher) {}
+}
+
 private struct TestViewModel {
     var onTap: () -> Void
     var onToggle: () -> Void

swift/WorkflowTesting/Sources/RenderExpectations.swift

@@ -102,11 +102,11 @@ public struct ExpectedWorker {
     }
 }
 
-public struct ExpectedSideEffect {
-    let key: AnyHashable
+public struct ExpectedSideEffect: Equatable {
+    private let key: AnyHashable
 
-    public init(key: AnyHashable) {
-        self.key = key
+    public init<S: SideEffect>(sideEffect: S) {
+        self.key = sideEffect
     }
 }
 

swift/WorkflowTesting/Sources/WorkflowRenderTester.swift

@@ -290,11 +290,10 @@
             }
         }
 
-        func runSideEffect(key: AnyHashable, action: (Lifetime) -> Void) {
-            guard let sideEffectIndex = expectations.expectedSideEffects.firstIndex(where: { (expectedSideEffect) -> Bool in
-                expectedSideEffect.key == key
-            }) else {
-                XCTFail("Unexpected side-effect during render \(key)", file: file, line: line)
+        func run<S>(_ sideEffect: S) where S: SideEffect {
+            guard let sideEffectIndex = expectations.expectedSideEffects.firstIndex(of: ExpectedSideEffect(sideEffect: sideEffect))
+            else {
+                XCTFail("Unexpected side-effect during render \(sideEffect)", file: file, line: line)
                 return
             }
 
@@ -344,7 +343,7 @@
 
             if !expectations.expectedSideEffects.isEmpty {
                 for expectedSideEffect in expectations.expectedSideEffects {
-                    XCTFail("Expected side-effect with key: \(expectedSideEffect.key)", file: file, line: line)
+                    XCTFail("Expected side-effect with key: \(expectedSideEffect)", file: file, line: line)
                 }
             }
         }

swift/WorkflowTesting/Tests/WorkflowRenderTesterTests.swift

@@ -16,6 +16,7 @@
 
 import ReactiveSwift
 import Workflow
+import class Workflow.Lifetime
 import WorkflowTesting
 import XCTest
 
@@ -85,7 +86,7 @@ final class WorkflowRenderTesterTests: XCTestCase {
 
         renderTester.render(
             with: RenderExpectations(expectedSideEffects: [
-                ExpectedSideEffect(key: TestSideEffectKey()),
+                ExpectedSideEffect(sideEffect: TestSideEffect()),
             ]),
             assertions: { _ in }
         )
@@ -324,8 +325,11 @@ private struct OutputWorkflow: Workflow {
     }
 }
 
-private struct TestSideEffectKey: Hashable {
+struct TestSideEffect: SideEffect {
     let key: String = "Test Side Effect"
+    func run() -> Lifetime {
+        Lifetime {}
+    }
 }
 
 private struct SideEffectWorkflow: Workflow {
@@ -334,7 +338,7 @@ private struct SideEffectWorkflow: Workflow {
     typealias Rendering = TestScreen
 
     func render(state: State, context: RenderContext<SideEffectWorkflow>) -> TestScreen {
-        context.runSideEffect(key: TestSideEffectKey()) { _ in }
+        context.run(sideEffect: TestSideEffect())
 
         return TestScreen(text: "value", tapped: {})
     }