refactor: DAG algorithm based state management

Examples/Packages/iOS/Sources/ExampleMovieDB/Atoms/MoviesAtoms.swift

@@ -15,8 +15,6 @@ final class MovieLoader: ObservableObject {
 
     func refresh() async {
         do {
-            pages = .suspending
-
             let page = try await api.getMovies(filter: filter, page: 1)
             pages = .success([page])
         }

Examples/Packages/iOS/Sources/ExampleMovieDB/Backend/APIClient.swift

@@ -12,7 +12,7 @@ protocol APIClientProtocol {
 }
 
 struct APIClient: APIClientProtocol {
-    private let session = URLSession.shared
+    private let session: URLSession = URLSession(configuration: .ephemeral)
     private let baseURL = URL(string: "https://api.themoviedb.org/3")!
     private let imageBaseURL = URL(string: "https://image.tmdb.org/t/p")!
     private let apiKey = "3de15b0402484d3d089399ea0b8d98f1"
@@ -30,8 +30,8 @@ struct APIClient: APIClientProtocol {
             imageBaseURL
             .appendingPathComponent(size.rawValue)
             .appendingPathComponent(path)
-
-        let (data, _) = try await session.data(from: url)
+        let request = URLRequest(url: url, cachePolicy: .returnCacheDataElseLoad, timeoutInterval: 10)
+        let (data, _) = try await session.data(for: request)
         return UIImage(data: data) ?? UIImage()
     }
 
@@ -63,7 +63,8 @@ struct APIClient: APIClientProtocol {
         Future { fulfill in
             Task {
                 do {
-                    let response: PagedResponse<Movie> = try await get(
+                    let response = try await get(
+                        PagedResponse<Movie>.self,
                         path: "search/movie",
                         parameters: ["query": query]
                     )
@@ -93,7 +94,7 @@ private extension APIClient {
 
         urlComponents.queryItems = queryItems
 
-        var urlRequest = URLRequest(url: urlComponents.url!)
+        var urlRequest = URLRequest(url: urlComponents.url!, cachePolicy: .reloadRevalidatingCacheData, timeoutInterval: 10)
         urlRequest.httpMethod = "GET"
 
         do {

Examples/Packages/iOS/Sources/ExampleMovieDB/Screens/MoviesScreen.swift

@@ -29,6 +29,12 @@ struct MoviesScreen: View {
                 FilterPicker()
 
                 switch loader.pages {
+                case .suspending:
+                    ProgressRow()
+
+                case .failure:
+                    CaveatRow(text: "Failed to get the data.")
+
                 case .success(let pages):
                     ForEach(pages, id: \.page) { response in
                         pageIndex(current: response.page, total: response.totalPages)
@@ -43,12 +49,6 @@ struct MoviesScreen: View {
                             await loader.loadNext()
                         }
                     }
-
-                case .failure:
-                    CaveatRow(text: "Failed to get the data.")
-
-                case .suspending:
-                    ProgressRow()
                 }
             }
         }
@@ -69,8 +69,11 @@ struct MoviesScreen: View {
         .task(id: loader.filter) {
             await loader.refresh()
         }
-        .refreshable { [loader] in
-            await loader.refresh()
+        .refreshable { [context] in
+            // NB: Implicitly capturing `self` causes memory leak with `refreshable`,
+            // and also capturing `loader` makes refresh doesn't work, so here reads
+            // `MovieLoader` via context.
+            await context.read(MovieLoaderAtom()).refresh()
         }
         .background {
             NavigationLink(

Examples/Packages/iOS/Sources/ExampleMovieDB/Views/CastList.swift

@@ -20,7 +20,7 @@ struct CastList: View {
             CaveatRow(text: "Failed to get casts data.")
 
         case .success(let casts) where casts.isEmpty:
-            CaveatRow(text: "There are no casts.")
+            CaveatRow(text: "No cast information is available.")
 
         case .success(let casts):
             ScrollView(.horizontal, showsIndicators: false) {

README.md

@@ -994,7 +994,7 @@ struct BooksView: View {
 
 Context available through the `@ViewContext` property wrapper when using atoms from a view. There is no specific API for this context.
 
-#### [AtomRelationContext](https://ra1028.github.io/swiftui-atom-properties/documentation/atoms/atomrelationcontext)
+#### [AtomTransactionContext](https://ra1028.github.io/swiftui-atom-properties/documentation/atoms/atomtransactioncontext)
 
 <details><summary><code>📖 Click to expand example code</code></summary>
 
@@ -1028,8 +1028,8 @@ Context passed as a parameter to the primary function of each atom type.
 
 |API|Use|
 |:--|:--|
-|[addTermination(_:)](https://ra1028.github.io/swiftui-atom-properties/documentation/atoms/atomrelationcontext/addtermination(_:))|Calls the passed closure when the atom is updated or is no longer used.|
-|[keepUntilTermination(_:)](https://ra1028.github.io/swiftui-atom-properties/documentation/atoms/atomrelationcontext/keepuntiltermination(_:))|Retains the given object instance until the atom is updated or is no longer used.|
+|[addTermination(_:)](https://ra1028.github.io/swiftui-atom-properties/documentation/atoms/atomtransactioncontext/addtermination(_:))|Calls the passed closure when the atom is updated or is no longer used.|
+|[keepUntilTermination(_:)](https://ra1028.github.io/swiftui-atom-properties/documentation/atoms/atomtransactioncontext/keepuntiltermination(_:))|Retains the given object instance until the atom is updated or is no longer used.|
 
 #### [AtomTestContext](https://ra1028.github.io/swiftui-atom-properties/documentation/atoms/atomtestcontext)
 

Sources/Atoms/Atom/AsyncSequenceAtom.swift

@@ -44,7 +44,7 @@
 /// }
 /// ```
 ///
-public protocol AsyncSequenceAtom: Atom where State == AsyncSequenceAtomState<Sequence> {
+public protocol AsyncSequenceAtom: Atom where Loader == AsyncSequenceAtomLoader<Sequence> {
     /// The type of asynchronous sequence that this atom manages.
     associatedtype Sequence: AsyncSequence
 
@@ -64,7 +64,7 @@ public protocol AsyncSequenceAtom: Atom where State == AsyncSequenceAtomState<Se
 
 public extension AsyncSequenceAtom {
     @MainActor
-    func makeState() -> State {
-        State(makeSequence: sequence)
+    var _loader: Loader {
+        Loader(makeSequence: sequence)
     }
 }

Sources/Atoms/Atom/Atom.swift

@@ -9,20 +9,19 @@ public protocol Atom {
     /// A type representing the stable identity of this atom.
     associatedtype Key: Hashable
 
-    /// A type of state that is an actual implementation of this atom.
-    associatedtype State: AtomState
+    /// A loader type that represents an actual implementation of the corresponding atom.
+    associatedtype Loader: AtomLoader
 
     /// A type of the context structure that to read, watch, and otherwise interacting
     /// with other atoms.
-    typealias Context = AtomRelationContext
+    typealias Context = AtomTransactionContext
 
     /// A boolean value indicating whether the atom value should be preserved even if
     /// no longer watched to.
     ///
     /// It's recommended to conform the ``KeepAlive`` to this atom, instead of overriding
     /// this property to return `true`.
     /// The default is `false`.
-    @MainActor
     static var shouldKeepAlive: Bool { get }
 
     /// A unique value used to identify the atom internally.
@@ -32,34 +31,12 @@ public protocol Atom {
     /// If this atom conforms to `Hashable`, it will adopt itself as the `key` by default.
     var key: Key { get }
 
-    /// Creates a new state that is an actual implementation of this atom.
-    ///
-    /// - Returns: A state object that handles internal process and a value.
-    @MainActor
-    func makeState() -> State
-
-    /// Returns a boolean value that determines whether it should notify the value update to
-    /// watchers with comparing the given old value and the new value.
-    ///
-    /// - Parameters:
-    ///   - newValue: The new value after update.
-    ///   - oldValue: The old value before update.
-    ///
-    /// - Returns: A boolean value that determines whether it should notify the value update
-    ///            to watchers.
-    @MainActor
-    func shouldNotifyUpdate(newValue: State.Value, oldValue: State.Value) -> Bool
-}
-
-public extension Atom {
+    /// A loader that represents an actual implementation of the corresponding atom.
     @MainActor
-    func shouldNotifyUpdate(newValue: State.Value, oldValue: State.Value) -> Bool {
-        true
-    }
+    var _loader: Loader { get }
 }
 
 public extension Atom {
-    @MainActor
     static var shouldKeepAlive: Bool {
         false
     }

Sources/Atoms/Atom/ModifiedAtom.swift

@@ -1,7 +1,7 @@
 /// An atom type that applies a modifier to an atom.
 ///
 /// Use ``Atom/modifier(_:)`` instead of using this atom directly.
-public struct ModifiedAtom<Node: Atom, Modifier: AtomModifier>: Atom where Node.State.Value == Modifier.Value {
+public struct ModifiedAtom<Node: Atom, Modifier: AtomModifier>: Atom where Node.Loader.Value == Modifier.Value {
     /// A type representing the stable identity of this atom.
     public struct Key: Hashable {
         private let atomKey: Node.Key
@@ -29,16 +29,8 @@ public struct ModifiedAtom<Node: Atom, Modifier: AtomModifier>: Atom where Node.
         Key(atomKey: atom.key, modifierKey: modifier.key)
     }
 
-    /// Creates a new state that is an actual implementation of this atom.
-    ///
-    /// - Returns: A state object that handles internal process and a value.
-    public func makeState() -> ModifiedAtomState<Node, Modifier> {
-        State(atom: atom, modifier: modifier)
-    }
-
-    /// Returns a boolean value that determines whether it should notify the value update to
-    /// watchers with comparing the given old value and the new value.
-    public func shouldNotifyUpdate(newValue: Modifier.ModifiedValue, oldValue: Modifier.ModifiedValue) -> Bool {
-        modifier.shouldNotifyUpdate(newValue: newValue, oldValue: oldValue)
+    /// A loader that represents an actual implementation of this atom.
+    public var _loader: ModifiedAtomLoader<Node, Modifier> {
+        Loader(atom: atom, modifier: modifier)
     }
 }

Sources/Atoms/Atom/ObservableObjectAtom.swift

@@ -48,7 +48,7 @@ import Combine
 /// }
 /// ```
 ///
-public protocol ObservableObjectAtom: Atom where State == ObservableObjectAtomState<ObjectType> {
+public protocol ObservableObjectAtom: Atom where Loader == ObservableObjectAtomLoader<ObjectType> {
     /// The type of observable object that this atom produces.
     associatedtype ObjectType: ObservableObject
 
@@ -67,7 +67,7 @@ public protocol ObservableObjectAtom: Atom where State == ObservableObjectAtomSt
 
 public extension ObservableObjectAtom {
     @MainActor
-    func makeState() -> State {
-        State(makeObject: object)
+    var _loader: Loader {
+        Loader(makeObject: object)
     }
 }

Sources/Atoms/Atom/PublisherAtom.swift

@@ -37,7 +37,7 @@ import Combine
 /// }
 /// ```
 ///
-public protocol PublisherAtom: Atom where State == PublisherAtomState<Publisher> {
+public protocol PublisherAtom: Atom where Loader == PublisherAtomLoader<Publisher> {
     /// The type of publisher that this atom manages.
     associatedtype Publisher: Combine.Publisher
 
@@ -57,7 +57,7 @@ public protocol PublisherAtom: Atom where State == PublisherAtomState<Publisher>
 
 public extension PublisherAtom {
     @MainActor
-    func makeState() -> State {
-        State(makePublisher: publisher)
+    var _loader: Loader {
+        Loader(makePublisher: publisher)
     }
 }

Sources/Atoms/Atom/StateAtom.swift

@@ -36,7 +36,7 @@
 /// }
 /// ```
 ///
-public protocol StateAtom: Atom where State == StateAtomState<Value> {
+public protocol StateAtom: Atom where Loader == ValueAtomLoader<Value> {
     /// The type of state value that this atom produces.
     associatedtype Value
 
@@ -77,8 +77,8 @@ public protocol StateAtom: Atom where State == StateAtomState<Value> {
 
 public extension StateAtom {
     @MainActor
-    func makeState() -> State {
-        State(getDefaultValue: defaultValue)
+    var _loader: Loader {
+        Loader(getValue: defaultValue)
     }
 
     @MainActor

Sources/Atoms/Atom/TaskAtom.swift

@@ -34,7 +34,7 @@
 /// }
 /// ```
 ///
-public protocol TaskAtom: Atom where State == TaskAtomState<Value> {
+public protocol TaskAtom: Atom where Loader == TaskAtomLoader<Value> {
     /// The type of value that this atom produces.
     associatedtype Value
 
@@ -53,7 +53,7 @@ public protocol TaskAtom: Atom where State == TaskAtomState<Value> {
 
 public extension TaskAtom {
     @MainActor
-    func makeState() -> State {
-        State(getValue: value)
+    var _loader: Loader {
+        Loader(getValue: value)
     }
 }

Sources/Atoms/Atom/ThrowingTaskAtom.swift

@@ -36,7 +36,7 @@
 /// }
 /// ```
 ///
-public protocol ThrowingTaskAtom: Atom where State == ThrowingTaskState<Value> {
+public protocol ThrowingTaskAtom: Atom where Loader == ThrowingTaskAtomLoader<Value> {
     /// The type of value that this atom produces.
     associatedtype Value
 
@@ -57,7 +57,7 @@ public protocol ThrowingTaskAtom: Atom where State == ThrowingTaskState<Value> {
 
 public extension ThrowingTaskAtom {
     @MainActor
-    func makeState() -> State {
-        State(getValue: value)
+    var _loader: Loader {
+        Loader(getValue: value)
     }
 }

Sources/Atoms/Atom/ValueAtom.swift

@@ -29,7 +29,7 @@
 /// }
 /// ```
 ///
-public protocol ValueAtom: Atom where State == ValueAtomState<Value> {
+public protocol ValueAtom: Atom where Loader == ValueAtomLoader<Value> {
     /// The type of value that this atom produces.
     associatedtype Value
 
@@ -48,7 +48,7 @@ public protocol ValueAtom: Atom where State == ValueAtomState<Value> {
 
 public extension ValueAtom {
     @MainActor
-    func makeState() -> State {
-        State(getValue: value)
+    var _loader: Loader {
+        Loader(getValue: value)
     }
 }

Sources/Atoms/AtomRelay.swift

@@ -39,7 +39,7 @@ public struct AtomRelay<Content: View>: View {
     private let content: Content
     private var observers = [AtomObserver]()
 
-    @Environment(\.atomStore)
+    @Environment(\.store)
     private var inheritedStore
 
     /// Creates an atom relay with the specified content that will be allowed to use atoms by
@@ -60,11 +60,8 @@ public struct AtomRelay<Content: View>: View {
     /// The content and behavior of the view.
     public var body: some View {
         content.environment(
-            \.atomStore,
-            Store(
-                parent: context?._store ?? inheritedStore,
-                observers: observers
-            )
+            \.store,
+            (context?._store ?? inheritedStore).relay(observers: observers)
         )
     }