Declare DependencyKeys namespace

Example/Example.xcodeproj/project.pbxproj

@@ -7,6 +7,12 @@
 	objects = {
 
 /* Begin PBXBuildFile section */
+		E189A4AE2776179D0090EC9F /* GlobalSchedulersClient.swift in Sources */ = {isa = PBXBuildFile; fileRef = E189A4AD2776179D0090EC9F /* GlobalSchedulersClient.swift */; };
+		E189A4AF2776179D0090EC9F /* GlobalSchedulersClient.swift in Sources */ = {isa = PBXBuildFile; fileRef = E189A4AD2776179D0090EC9F /* GlobalSchedulersClient.swift */; };
+		E189A4B1277619040090EC9F /* NoOptionsScheduler.swift in Sources */ = {isa = PBXBuildFile; fileRef = E189A4B0277619040090EC9F /* NoOptionsScheduler.swift */; };
+		E189A4B2277619040090EC9F /* NoOptionsScheduler.swift in Sources */ = {isa = PBXBuildFile; fileRef = E189A4B0277619040090EC9F /* NoOptionsScheduler.swift */; };
+		E189A4B427761B9F0090EC9F /* Helpers.swift in Sources */ = {isa = PBXBuildFile; fileRef = E189A4B327761B9F0090EC9F /* Helpers.swift */; };
+		E189A4B527761B9F0090EC9F /* Helpers.swift in Sources */ = {isa = PBXBuildFile; fileRef = E189A4B327761B9F0090EC9F /* Helpers.swift */; };
 		E972F1FD26A2B74A00504D39 /* ExampleApp.swift in Sources */ = {isa = PBXBuildFile; fileRef = E972F1EA26A2B74A00504D39 /* ExampleApp.swift */; };
 		E972F1FE26A2B74B00504D39 /* ExampleApp.swift in Sources */ = {isa = PBXBuildFile; fileRef = E972F1EA26A2B74A00504D39 /* ExampleApp.swift */; };
 		E972F20126A2B74B00504D39 /* Assets.xcassets in Resources */ = {isa = PBXBuildFile; fileRef = E972F1EC26A2B74A00504D39 /* Assets.xcassets */; };
@@ -24,6 +30,9 @@
 /* End PBXBuildFile section */
 
 /* Begin PBXFileReference section */
+		E189A4AD2776179D0090EC9F /* GlobalSchedulersClient.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = GlobalSchedulersClient.swift; sourceTree = "<group>"; };
+		E189A4B0277619040090EC9F /* NoOptionsScheduler.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = NoOptionsScheduler.swift; sourceTree = "<group>"; };
+		E189A4B327761B9F0090EC9F /* Helpers.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Helpers.swift; sourceTree = "<group>"; };
 		E972F1EA26A2B74A00504D39 /* ExampleApp.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ExampleApp.swift; sourceTree = "<group>"; };
 		E972F1EC26A2B74A00504D39 /* Assets.xcassets */ = {isa = PBXFileReference; lastKnownFileType = folder.assetcatalog; path = Assets.xcassets; sourceTree = "<group>"; };
 		E972F1F126A2B74A00504D39 /* Example.app */ = {isa = PBXFileReference; explicitFileType = wrapper.application; includeInIndex = 0; path = Example.app; sourceTree = BUILT_PRODUCTS_DIR; };
@@ -75,6 +84,9 @@
 				E972F21B26A2B9B900504D39 /* Level1Feature.swift */,
 				E972F21E26A2BA8400504D39 /* Level2Feature.swift */,
 				E972F22126A2C72200504D39 /* SharedDependencies.swift */,
+				E189A4AD2776179D0090EC9F /* GlobalSchedulersClient.swift */,
+				E189A4B0277619040090EC9F /* NoOptionsScheduler.swift */,
+				E189A4B327761B9F0090EC9F /* Helpers.swift */,
 				E972F1EA26A2B74A00504D39 /* ExampleApp.swift */,
 				E972F1EC26A2B74A00504D39 /* Assets.xcassets */,
 			);
@@ -222,6 +234,9 @@
 				E972F21C26A2B9B900504D39 /* Level1Feature.swift in Sources */,
 				E972F21F26A2BA8400504D39 /* Level2Feature.swift in Sources */,
 				E972F21926A2B9A700504D39 /* Level0Feature.swift in Sources */,
+				E189A4B427761B9F0090EC9F /* Helpers.swift in Sources */,
+				E189A4B1277619040090EC9F /* NoOptionsScheduler.swift in Sources */,
+				E189A4AE2776179D0090EC9F /* GlobalSchedulersClient.swift in Sources */,
 				E972F22226A2C72200504D39 /* SharedDependencies.swift in Sources */,
 				E972F1FD26A2B74A00504D39 /* ExampleApp.swift in Sources */,
 			);
@@ -234,6 +249,9 @@
 				E972F21D26A2B9B900504D39 /* Level1Feature.swift in Sources */,
 				E972F22026A2BA8400504D39 /* Level2Feature.swift in Sources */,
 				E972F21A26A2B9A700504D39 /* Level0Feature.swift in Sources */,
+				E189A4B527761B9F0090EC9F /* Helpers.swift in Sources */,
+				E189A4B2277619040090EC9F /* NoOptionsScheduler.swift in Sources */,
+				E189A4AF2776179D0090EC9F /* GlobalSchedulersClient.swift in Sources */,
 				E972F22326A2C72200504D39 /* SharedDependencies.swift in Sources */,
 				E972F1FE26A2B74B00504D39 /* ExampleApp.swift in Sources */,
 			);

Example/Shared/ExampleApp.swift

@@ -2,21 +2,20 @@ import ComposableArchitecture
 import ComposableEnvironment
 import SwiftUI
 
-let store = Store<Level0State, Level0Action>(
-  initialState:
-  .init(level1: .init(
+let store = Store(
+  initialState: Level0State(level1: .init(
     first: .init(randomNumber: nil),
     second: .init(randomNumber: nil)
   )),
   reducer: level0Reducer,
-  environment: .init()
+  environment: Level0Environment()
 )
 
 @main
 struct ExampleApp: App {
   var body: some Scene {
     WindowGroup {
-      Level0View(store: store)
+      Level0View(store)
     }
   }
 }

Example/Shared/GlobalSchedulersClient.swift

@@ -0,0 +1,24 @@
+import Combine
+import Foundation
+
+public struct GlobalSchedulersClient {
+  public init(
+    _ scheduler: @escaping (DispatchQoS.QoSClass) -> NoOptionsSchedulerOf<DispatchQueue>
+  ) {
+    self.scheduler = scheduler
+  }
+
+  public var scheduler: (DispatchQoS.QoSClass) -> NoOptionsSchedulerOf<DispatchQueue>
+
+  public func callAsFunction(
+    qos: DispatchQoS.QoSClass = .default
+  ) -> NoOptionsSchedulerOf<DispatchQueue> {
+    return scheduler(qos)
+  }
+}
+
+extension GlobalSchedulersClient {
+  public static let live: GlobalSchedulersClient = .init { qos in
+    return DispatchQueue.global(qos: qos).ignoreOptions()
+  }
+}

Example/Shared/Helpers.swift

@@ -0,0 +1,6 @@
+// for some reason ReferenceWritableKeyPath is not converible to function via type-inference in pullback
+func get<Object: AnyObject, Value>(
+  _ keyPath: ReferenceWritableKeyPath<Object, Value>
+) -> (Object) -> Value {
+  return { $0[keyPath: keyPath] }
+}

Example/Shared/Level0Feature.swift

@@ -17,58 +17,83 @@ enum Level0Action {
 }
 
 class Level0Environment: ComposableEnvironment {
-  // Dependencies
-  @Dependency(\.mainQueue) var main
-  @Dependency(\.backgroundQueue) var background
-
-  // Derived Environments
-  @DerivedEnvironment<Level1Environment> var level1
+  // This style of using property-wrappers allows to
+  // find derived environment type a bit easier, then DerivedEnvironment<Type>
+  // and visual composition is a bit better, so we keep wrapper as a simple annotation
+  // and all of the information that is related to a property is on one line
+  @DerivedEnvironment
+  var schedulers: StoreSchedulers
+
+  @DerivedEnvironment
+  var level1: Level1Environment
 }
 
-let level0Reducer = Reducer<Level0State, Level0Action, Level0Environment>.combine(
-  level1Reducer.pullback(state: \.level1,
-                         action: /Level0Action.level1,
-                         environment: \.level1),
-  Reducer<Level0State, Level0Action, Level0Environment> {
-    state, action, environment in
+// You may prefer to define type explicitly to avoid using `get` helper
+//
+// let level0Reducer = Reducer<
+//   Level0State,
+//   Level0Action,
+//   Level0Environment
+// >.combine(
+//   level1Reducer.pullback(
+//     state: \.level1,
+//     action: /Level0Action.level1,
+//     environment: \.level1
+//   ),
+//   ...
+// )
+
+let level0Reducer = Reducer.combine(
+  level1Reducer.pullback(
+    state: \Level0State.level1,
+    action: /Level0Action.level1,
+    environment: get(\Level0Environment.level1)
+  ),
+  Reducer { state, action, environment in
     switch action {
     case .isReady:
       state.isReady = true
       return .none
+
     case .level1:
       return .none
+
     case .onAppear:
       return Effect(value: .isReady)
-        .delay(for: 1, scheduler: environment.background) // Simulate something lengthy…
-        .receive(on: environment.main)
+        .delay(for: 1, scheduler: environment.schedulers.background()) // Simulate something lengthy…
+        .receive(on: environment.schedulers.main)
         .eraseToEffect()
-
-      // Alternatively, we can directly tap into the environment's dependepencies using
-      // their global property name, meaning that we can even bypass declarations like
-      // `@Dependency(\.mainQueue) var main` in the environment to write:
-      //
-      //   return Effect(value: .isReady)
-      //     .delay(for: 1, scheduler: environment.backgroundQueue)
-      //     .receive(on: environment.mainQueue)
-      //     .eraseToEffect()
     }
   }
 )
 
+// Alternatively, we can directly tap into the environment's dependepencies using
+// their global property name, meaning that we can even bypass declarations like
+// `@Dependency(\.mainQueue) var main` in the environment to write:
+//
+//   return Effect(value: .isReady)
+//     .delay(for: 1, scheduler: environment.globalSchedulers(qos: .default))
+//     .receive(on: environment.mainQueue)
+//     .eraseToEffect()
+
 struct Level0View: View {
   let store: Store<Level0State, Level0Action>
-  init(store: Store<Level0State, Level0Action>) {
+
+  init(_ store: Store<Level0State, Level0Action>) {
     self.store = store
   }
-
+  
   var body: some View {
     WithViewStore(store) { viewStore in
       VStack {
         Text("Random numbers")
           .font(.title)
-        Level1View(store: store.scope(state: \.level1, action: Level0Action.level1))
-          .padding()
-          .disabled(!viewStore.isReady)
+        Level1View(store.scope(
+          state: \.level1,
+          action: Level0Action.level1
+        ))
+        .padding()
+        .disabled(!viewStore.isReady)
       }
       .onAppear { viewStore.send(.onAppear) }
       .fixedSize()
@@ -78,30 +103,28 @@ struct Level0View: View {
 
 struct Level0View_Preview: PreviewProvider {
   static var previews: some View {
-    Level0View(store:
-      .init(initialState:
-        .init(
-          level1: .init(
-            first: .init(randomNumber: 6),
-            second: .init(randomNumber: nil)
-          )
-        ),
-        reducer: level0Reducer,
-        environment: Level0Environment() // Swift ≥ 5.4 can use .init()
-          .with(\.mainQueue, .immediate)
-          .with(\.backgroundQueue, .immediate)
-          // We can set the value of `rng` even if Level0Environment doesn't have a `rng` property:
-          .with(\.rng) { 4 })
-    )
-    Level0View(store:
-      .init(initialState:
-        .init(level1: .init(
-          first: .init(randomNumber: nil),
+    Level0View(Store(
+      initialState: .init(
+        level1: .init(
+          first: .init(randomNumber: 6),
           second: .init(randomNumber: nil)
-        )),
-        reducer: level0Reducer,
-        // An environment default dependencies:
-        environment: .init())
-    )
+        )
+      ),
+      reducer: level0Reducer,
+      environment: Level0Environment() // Swift ≥ 5.4 can use .init()
+        .with(\.eventHandlingScheduler, AnyScheduler.immediate.ignoreOptions())
+        .with(\.globalSchedulers, .init { _ in AnyScheduler.immediate.ignoreOptions() })
+        // We can set the value of `rng` even if Level0Environment doesn't have a `rng` property:
+        .with(\.rng) { 4 }
+    ))
+    Level0View(Store(
+      initialState:.init(level1: .init(
+        first: .init(randomNumber: nil),
+        second: .init(randomNumber: nil)
+      )),
+      reducer: level0Reducer,
+      // An environment default dependencies:
+      environment: .init()
+    ))
   }
 }