refactor: enable injecting a custom State type into Channel

This will enable testing to expose a leaked CheckedContinuation.

Author: Brandon Schoenfeld

Sources/AsyncDataLoader/Channel/Channel.swift

@@ -1,5 +1,20 @@
-actor Channel<Success: Sendable, Failure: Error>: Sendable {
-    private var state = State<Success, Failure>()
+actor Channel<
+    Success: Sendable,
+    Failure: Error,
+    ChannelState: Stateful
+>: Sendable where ChannelState.Success == Success, ChannelState.Failure == Failure {
+    private var state: ChannelState
+
+    init(_ state: ChannelState) {
+        self.state = state
+    }
+}
+
+extension Channel where ChannelState == State<Success, Failure> {
+    /// Default initializer: uses DefaultState
+    init() {
+        self.init(State<Success, Failure>())
+    }
 }
 
 extension Channel {

Sources/AsyncDataLoader/Channel/State.swift

@@ -1,6 +1,20 @@
 typealias Waiter<Success, Failure> = CheckedContinuation<Success, Error>
 
-actor State<Success, Failure> {
+protocol Stateful: Actor {
+    associatedtype Success: Sendable
+    associatedtype Failure: Sendable
+
+    var waiters: [Waiter<Success, Failure>] { get set }
+    var result: Success? { get set }
+    var failure: Failure? { get set }
+
+    func setResult(result: Success) async
+    func setFailure(failure: Failure) async
+    func appendWaiters(waiters: Waiter<Success, Failure>...) async
+    func removeAllWaiters() async
+}
+
+actor State<Success, Failure>: Stateful {
     var waiters = [Waiter<Success, Failure>]()
     var result: Success?
     var failure: Failure?

Sources/AsyncDataLoader/DataLoader.swift

@@ -10,7 +10,7 @@ public typealias BatchLoadFunction<Key: Hashable & Sendable, Value: Sendable> =
     @Sendable (_ keys: [Key]) async throws -> [DataLoaderValue<Value>]
 private typealias LoaderQueue<Key: Hashable & Sendable, Value: Sendable> = [(
     key: Key,
-    channel: Channel<Value, Error>
+    channel: Channel<Value, Error, State<Value, Error>>
 )]
 
 /// DataLoader creates a public API for loading data from a particular
@@ -25,7 +25,7 @@ public actor DataLoader<Key: Hashable & Sendable, Value: Sendable> {
     private let batchLoadFunction: BatchLoadFunction<Key, Value>
     private let options: DataLoaderOptions<Key, Value>
 
-    private var cache = [Key: Channel<Value, Error>]()
+    private var cache = [Key: Channel<Value, Error, State<Value, Error>>]()
     private var queue = LoaderQueue<Key, Value>()
 
     private var dispatchScheduled = false
@@ -46,7 +46,7 @@ public actor DataLoader<Key: Hashable & Sendable, Value: Sendable> {
             return try await cached.value
         }
 
-        let channel = Channel<Value, Error>()
+        let channel = Channel<Value, Error, State<Value, Error>>()
 
         if options.batchingEnabled {
             queue.append((key: key, channel: channel))
@@ -148,7 +148,7 @@ public actor DataLoader<Key: Hashable & Sendable, Value: Sendable> {
         let cacheKey = options.cacheKeyFunction?(key) ?? key
 
         if cache[cacheKey] == nil {
-            let channel = Channel<Value, Error>()
+            let channel = Channel<Value, Error, State<Value, Error>>()
 
             Task.detached {
                 await channel.fulfill(value)