Turn ValueObservationScheduler into a protocol

groue · groue · commit 0dd17a9a168f · 2022-12-29T12:38:06.000+01:00
diff --git a/GRDB/Core/DatabasePool.swift b/GRDB/Core/DatabasePool.swift
@@ -644,7 +644,7 @@ extension DatabasePool: DatabaseReader {
     
     public func _add<Reducer: ValueReducer>(
         observation: ValueObservation<Reducer>,
-        scheduling scheduler: ValueObservationScheduler,
+        scheduling scheduler: some ValueObservationScheduler,
         onChange: @escaping (Reducer.Value) -> Void)
     -> AnyDatabaseCancellable
     {
@@ -675,7 +675,7 @@ extension DatabasePool: DatabaseReader {
     /// the writer.
     private func _addConcurrent<Reducer: ValueReducer>(
         observation: ValueObservation<Reducer>,
-        scheduling scheduler: ValueObservationScheduler,
+        scheduling scheduler: some ValueObservationScheduler,
         onChange: @escaping (Reducer.Value) -> Void)
     -> AnyDatabaseCancellable
     {
diff --git a/GRDB/Core/DatabaseQueue.swift b/GRDB/Core/DatabaseQueue.swift
@@ -294,7 +294,7 @@ extension DatabaseQueue: DatabaseReader {
     
     public func _add<Reducer: ValueReducer>(
         observation: ValueObservation<Reducer>,
-        scheduling scheduler: ValueObservationScheduler,
+        scheduling scheduler: some ValueObservationScheduler,
         onChange: @escaping (Reducer.Value) -> Void)
     -> AnyDatabaseCancellable
     {
diff --git a/GRDB/Core/DatabaseReader.swift b/GRDB/Core/DatabaseReader.swift
@@ -325,7 +325,7 @@ public protocol DatabaseReader: AnyObject, Sendable {
     /// - returns: A DatabaseCancellable that can stop the observation.
     func _add<Reducer: ValueReducer>(
         observation: ValueObservation<Reducer>,
-        scheduling scheduler: ValueObservationScheduler,
+        scheduling scheduler: some ValueObservationScheduler,
         onChange: @escaping (Reducer.Value) -> Void)
     -> AnyDatabaseCancellable
 }
@@ -584,7 +584,7 @@ extension DatabaseReader {
     /// initial value.
     func _addReadOnly<Reducer: ValueReducer>(
         observation: ValueObservation<Reducer>,
-        scheduling scheduler: ValueObservationScheduler,
+        scheduling scheduler: some ValueObservationScheduler,
         onChange: @escaping (Reducer.Value) -> Void)
     -> AnyDatabaseCancellable
     {
@@ -676,7 +676,7 @@ extension AnyDatabaseReader: DatabaseReader {
     
     public func _add<Reducer: ValueReducer>(
         observation: ValueObservation<Reducer>,
-        scheduling scheduler: ValueObservationScheduler,
+        scheduling scheduler: some ValueObservationScheduler,
         onChange: @escaping (Reducer.Value) -> Void)
     -> AnyDatabaseCancellable
     {
diff --git a/GRDB/Core/DatabaseSnapshot.swift b/GRDB/Core/DatabaseSnapshot.swift
@@ -170,7 +170,7 @@ extension DatabaseSnapshot: DatabaseSnapshotReader {
     
     public func _add<Reducer: ValueReducer>(
         observation: ValueObservation<Reducer>,
-        scheduling scheduler: ValueObservationScheduler,
+        scheduling scheduler: some ValueObservationScheduler,
         onChange: @escaping (Reducer.Value) -> Void)
     -> AnyDatabaseCancellable
     {
diff --git a/GRDB/Core/DatabaseSnapshotPool.swift b/GRDB/Core/DatabaseSnapshotPool.swift
@@ -329,7 +329,7 @@ extension DatabaseSnapshotPool: DatabaseSnapshotReader {
     
     public func _add<Reducer>(
         observation: ValueObservation<Reducer>,
-        scheduling scheduler: ValueObservationScheduler,
+        scheduling scheduler: some ValueObservationScheduler,
         onChange: @escaping (Reducer.Value) -> Void)
     -> AnyDatabaseCancellable where Reducer: ValueReducer
     {
diff --git a/GRDB/Core/DatabaseWriter.swift b/GRDB/Core/DatabaseWriter.swift
@@ -531,7 +531,7 @@ extension DatabaseWriter {
     /// was modified.
     func _addWriteOnly<Reducer: ValueReducer>(
         observation: ValueObservation<Reducer>,
-        scheduling scheduler: ValueObservationScheduler,
+        scheduling scheduler: some ValueObservationScheduler,
         onChange: @escaping (Reducer.Value) -> Void)
     -> AnyDatabaseCancellable
     {
@@ -993,7 +993,7 @@ extension AnyDatabaseWriter: DatabaseReader {
     
     public func _add<Reducer: ValueReducer>(
         observation: ValueObservation<Reducer>,
-        scheduling scheduler: ValueObservationScheduler,
+        scheduling scheduler: some ValueObservationScheduler,
         onChange: @escaping (Reducer.Value) -> Void)
     -> AnyDatabaseCancellable
     {
diff --git a/GRDB/ValueObservation/Observers/ValueConcurrentObserver.swift b/GRDB/ValueObservation/Observers/ValueConcurrentObserver.swift
@@ -18,13 +18,13 @@ import Foundation
 /// reducing stage.
 ///
 /// **Notify** is calling user callbacks, in case of database change or error.
-final class ValueConcurrentObserver<Reducer: ValueReducer> {
+final class ValueConcurrentObserver<Reducer: ValueReducer, Scheduler: ValueObservationScheduler> {
     // MARK: - Configuration
     //
     // Configuration is not mutable.
     
     /// How to schedule observed values and errors.
-    private let scheduler: ValueObservationScheduler
+    private let scheduler: Scheduler
     
     /// Configures the tracked database region.
     private let trackingMode: ValueObservationTrackingMode
@@ -141,7 +141,7 @@ final class ValueConcurrentObserver<Reducer: ValueReducer> {
     
     init(
         dbPool: DatabasePool,
-        scheduler: ValueObservationScheduler,
+        scheduler: Scheduler,
         trackingMode: ValueObservationTrackingMode,
         reducer: Reducer,
         events: ValueObservationEvents,
diff --git a/GRDB/ValueObservation/Observers/ValueWriteOnlyObserver.swift b/GRDB/ValueObservation/Observers/ValueWriteOnlyObserver.swift
@@ -18,13 +18,13 @@ import Foundation
 /// reducing stage.
 ///
 /// **Notify** is calling user callbacks, in case of database change or error.
-final class ValueWriteOnlyObserver<Writer: DatabaseWriter, Reducer: ValueReducer> {
+final class ValueWriteOnlyObserver<Writer: DatabaseWriter, Reducer: ValueReducer, Scheduler: ValueObservationScheduler> {
     // MARK: - Configuration
     //
     // Configuration is not mutable.
     
     /// How to schedule observed values and errors.
-    private let scheduler: ValueObservationScheduler
+    private let scheduler: Scheduler
     
     /// Configures the tracked database region.
     private let trackingMode: ValueObservationTrackingMode
@@ -141,7 +141,7 @@ final class ValueWriteOnlyObserver<Writer: DatabaseWriter, Reducer: ValueReducer
     
     init(
         writer: Writer,
-        scheduler: ValueObservationScheduler,
+        scheduler: Scheduler,
         readOnly: Bool,
         trackingMode: ValueObservationTrackingMode,
         reducer: Reducer,
diff --git a/GRDB/ValueObservation/SharedValueObservation.swift b/GRDB/ValueObservation/SharedValueObservation.swift
@@ -121,7 +121,7 @@ extension ValueObservation {
     /// - returns: A `SharedValueObservation`
     public func shared(
         in reader: some DatabaseReader,
-        scheduling scheduler: ValueObservationScheduler = .async(onQueue: .main),
+        scheduling scheduler: some ValueObservationScheduler = .async(onQueue: .main),
         extent: SharedValueObservationExtent = .whileObserved)
     -> SharedValueObservation<Reducer.Value>
     where Reducer: ValueReducer
@@ -168,7 +168,7 @@ extension ValueObservation {
 /// let cancellable2 = ValueObservation.tracking { db in ... }.shared(in: dbQueue).start(...)
 /// ```
 public final class SharedValueObservation<Element> {
-    private let scheduler: ValueObservationScheduler
+    private let scheduler: any ValueObservationScheduler
     private let extent: SharedValueObservationExtent
     private let startObservation: ValueObservationStart<Element>
     private let lock = NSRecursiveLock() // support synchronous observation events
@@ -190,7 +190,7 @@ public final class SharedValueObservation<Element> {
     }
     
     fileprivate init(
-        scheduling scheduler: ValueObservationScheduler,
+        scheduling scheduler: some ValueObservationScheduler,
         extent: SharedValueObservationExtent,
         startObservation: @escaping ValueObservationStart<Element>)
     {
diff --git a/GRDB/ValueObservation/ValueObservation.swift b/GRDB/ValueObservation/ValueObservation.swift
@@ -475,7 +475,7 @@ extension ValueObservation: Refinable {
     /// - returns: A DatabaseCancellable that can stop the observation.
     public func start(
         in reader: some DatabaseReader,
-        scheduling scheduler: ValueObservationScheduler = .async(onQueue: .main),
+        scheduling scheduler: some ValueObservationScheduler = .async(onQueue: .main),
         onError: @escaping (Error) -> Void,
         onChange: @escaping (Reducer.Value) -> Void)
     -> AnyDatabaseCancellable
@@ -637,7 +637,7 @@ extension ValueObservation {
     @available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
     public func values(
         in reader: some DatabaseReader,
-        scheduling scheduler: ValueObservationScheduler = .async(onQueue: .main),
+        scheduling scheduler: some ValueObservationScheduler = .async(onQueue: .main),
         bufferingPolicy: AsyncValueObservation<Reducer.Value>.BufferingPolicy = .unbounded)
     -> AsyncValueObservation<Reducer.Value>
     where Reducer: ValueReducer
@@ -774,7 +774,7 @@ extension ValueObservation {
     @available(OSX 10.15, iOS 13, tvOS 13, watchOS 6, *)
     public func publisher(
         in reader: some DatabaseReader,
-        scheduling scheduler: ValueObservationScheduler = .async(onQueue: .main))
+        scheduling scheduler: some ValueObservationScheduler = .async(onQueue: .main))
     -> DatabasePublishers.Value<Reducer.Value>
     where Reducer: ValueReducer
     {
diff --git a/GRDB/ValueObservation/ValueObservationScheduler.swift b/GRDB/ValueObservation/ValueObservationScheduler.swift
@@ -1,68 +1,26 @@
 import Dispatch
 import Foundation
 
-/// ValueObservationScheduler determines how `ValueObservation` notifies its
-/// fresh values.
-public class ValueObservationScheduler {
-    private let impl: any ValueObservationSchedulerImpl
-    
-    private init(impl: any ValueObservationSchedulerImpl) {
-        self.impl = impl
-    }
-    
-    func schedule(_ action: @escaping () -> Void) {
-        impl.schedule(action)
-    }
-    
+/// A type that determines when `ValueObservation` notifies its fresh values.
+///
+/// ## Topics
+///
+/// ### Built-In Schedulers
+///
+/// - ``async(onQueue:)``
+/// - ``immediate``
+/// - ``AsyncValueObservationScheduler``
+/// - ``ImmediateValueObservationScheduler``
+public protocol ValueObservationScheduler {
     /// Returns whether the initial value should be immediately notified.
     ///
-    /// If true, then this method was called on the main thread.
-    func immediateInitialValue() -> Bool {
-        impl.immediateInitialValue()
-    }
-    
-    /// A scheduler which asynchronously notifies fresh value of the
-    /// given DispatchQueue.
-    ///
-    /// For example:
-    ///
-    ///     let observation = ValueObservation.tracking { db in
-    ///         try Player.fetchAll(db)
-    ///     }
-    ///
-    ///     let cancellable = try observation.start(
-    ///         in: dbQueue,
-    ///         scheduling: .async(onQueue: .main),
-    ///         onError: { error in ... },
-    ///         onChange: { (players: [Player]) in
-    ///             print("fresh players: \(players)")
-    ///         })
-    public static func async(onQueue queue: DispatchQueue) -> ValueObservationScheduler {
-        ValueObservationScheduler(impl: queue)
-    }
-    
-    /// A scheduler which notifies all values on the main queue. The first one
-    /// is immediately notified when the start() method is called.
-    ///
-    /// For example:
-    ///
-    ///     let observation = ValueObservation.tracking { db in
-    ///         try Player.fetchAll(db)
-    ///     }
-    ///
-    ///     let cancellable = try observation.start(
-    ///         in: dbQueue,
-    ///         scheduling: .immediate,
-    ///         onError: { error in ... },
-    ///         onChange: { (players: [Player]) in
-    ///             print("fresh players: \(players)")
-    ///         })
-    ///     // <- here "fresh players" is already printed.
-    ///
-    /// - important: this scheduler requires that the observation is started
-    ///  from the main queue. A fatal error is raised otherwise.
-    public static let immediate = ValueObservationScheduler(impl: ImmediateImpl())
+    /// If the result is true, then this method was called on the main thread.
+    func immediateInitialValue() -> Bool
     
+    func schedule(_ action: @escaping () -> Void)
+}
+
+extension ValueObservationScheduler {
     func scheduleInitial(_ action: @escaping () -> Void) {
         if immediateInitialValue() {
             action()
@@ -72,34 +30,92 @@ public class ValueObservationScheduler {
     }
 }
 
-private protocol ValueObservationSchedulerImpl {
-    func schedule(_ action: @escaping () -> Void)
+// MARK: - AsyncValueObservationScheduler
+
+/// A scheduler that asynchronously notifies fresh value of a `DispatchQueue`.
+public struct AsyncValueObservationScheduler: ValueObservationScheduler {
+    var queue: DispatchQueue
     
-    /// Returns whether the initial value should be immediately notified.
-    ///
-    /// If true, then this method was called on the main thread.
-    func immediateInitialValue() -> Bool
+    public init(queue: DispatchQueue) {
+        self.queue = queue
+    }
+    
+    public func immediateInitialValue() -> Bool { false }
+    
+    public func schedule(_ action: @escaping () -> Void) {
+        queue.async(execute: action)
+    }
 }
 
-private struct ImmediateImpl: ValueObservationSchedulerImpl {
-    func schedule(_ action: @escaping () -> Void) {
-        DispatchQueue.main.async(execute: action)
+extension ValueObservationScheduler where Self == AsyncValueObservationScheduler {
+    /// A scheduler that asynchronously notifies fresh value of the
+    /// given `DispatchQueue`.
+    ///
+    /// For example:
+    ///
+    /// ```swift
+    /// let observation = ValueObservation.tracking { db in
+    ///     try Player.fetchAll(db)
+    /// }
+    ///
+    /// let cancellable = try observation.start(
+    ///     in: dbQueue,
+    ///     scheduling: .async(onQueue: .main),
+    ///     onError: { error in ... },
+    ///     onChange: { (players: [Player]) in
+    ///         print("fresh players: \(players)")
+    ///     })
+    /// ```
+    public static func async(onQueue queue: DispatchQueue) -> AsyncValueObservationScheduler {
+        AsyncValueObservationScheduler(queue: queue)
     }
+}
+
+// MARK: - ImmediateValueObservationScheduler
+
+/// A scheduler that notifies all values on the main `DispatchQueue`. The
+/// first value is immediately notified when the `ValueObservation`
+/// is started.
+public struct ImmediateValueObservationScheduler: ValueObservationScheduler {
+    public init() { }
     
-    func immediateInitialValue() -> Bool {
+    public func immediateInitialValue() -> Bool {
         GRDBPrecondition(
             Thread.isMainThread,
             "ValueObservation must be started from the main thread.")
         return true
     }
+    
+    public func schedule(_ action: @escaping () -> Void) {
+        DispatchQueue.main.async(execute: action)
+    }
 }
 
-extension DispatchQueue: ValueObservationSchedulerImpl {
-    func schedule(_ action: @escaping () -> Void) {
-        async(execute: action)
-    }
-    
-    func immediateInitialValue() -> Bool {
-        false
+extension ValueObservationScheduler where Self == ImmediateValueObservationScheduler {
+    /// A scheduler that notifies all values on the main `DispatchQueue`. The
+    /// first value is immediately notified when the `ValueObservation`
+    /// is started.
+    ///
+    /// For example:
+    ///
+    /// ```swift
+    /// let observation = ValueObservation.tracking { db in
+    ///     try Player.fetchAll(db)
+    /// }
+    ///
+    /// let cancellable = try observation.start(
+    ///     in: dbQueue,
+    ///     scheduling: .immediate,
+    ///     onError: { error in ... },
+    ///     onChange: { (players: [Player]) in
+    ///         print("fresh players: \(players)")
+    ///     })
+    /// // <- here "fresh players" is already printed.
+    /// ```
+    ///
+    /// - important: this scheduler requires that the observation is started
+    ///  from the main queue. A fatal error is raised otherwise.
+    public static var immediate: ImmediateValueObservationScheduler {
+        ImmediateValueObservationScheduler()
     }
 }
diff --git a/Tests/GRDBTests/ValueObservationRecorder.swift b/Tests/GRDBTests/ValueObservationRecorder.swift

Original file line number	Diff line number	Diff line change
`@@ -294,7 +294,7 @@ extension DatabaseQueue: DatabaseReader {`
`294`	`294`
`295`	`295`	`public func _add<Reducer: ValueReducer>(`
`296`	`296`	`observation: ValueObservation<Reducer>,`
`297`		`- scheduling scheduler: ValueObservationScheduler,`
	`297`	`+ scheduling scheduler: some ValueObservationScheduler,`
`298`	`298`	`onChange: @escaping (Reducer.Value) -> Void)`
`299`	`299`	`-> AnyDatabaseCancellable`
`300`	`300`	`{`
Original file line number	Diff line number	Diff line change
`@@ -170,7 +170,7 @@ extension DatabaseSnapshot: DatabaseSnapshotReader {`
`170`	`170`
`171`	`171`	`public func _add<Reducer: ValueReducer>(`
`172`	`172`	`observation: ValueObservation<Reducer>,`
`173`		`- scheduling scheduler: ValueObservationScheduler,`
	`173`	`+ scheduling scheduler: some ValueObservationScheduler,`
`174`	`174`	`onChange: @escaping (Reducer.Value) -> Void)`
`175`	`175`	`-> AnyDatabaseCancellable`
`176`	`176`	`{`
Original file line number	Diff line number	Diff line change
`@@ -329,7 +329,7 @@ extension DatabaseSnapshotPool: DatabaseSnapshotReader {`
`329`	`329`
`330`	`330`	`public func _add<Reducer>(`
`331`	`331`	`observation: ValueObservation<Reducer>,`
`332`		`- scheduling scheduler: ValueObservationScheduler,`
	`332`	`+ scheduling scheduler: some ValueObservationScheduler,`
`333`	`333`	`onChange: @escaping (Reducer.Value) -> Void)`
`334`	`334`	`-> AnyDatabaseCancellable where Reducer: ValueReducer`
`335`	`335`	`{`