Add variadic generics version of `Defaults.updates()` (#191)

Sources/Defaults/Defaults.swift

@@ -292,13 +292,64 @@ extension Defaults {
 		}
 	}
 
-	// We still keep this as it can be useful to pass a dynamic array of keys.
 	/**
 	Observe updates to multiple stored values.
 
 	- Parameter keys: The keys to observe updates from.
 	- Parameter initial: Trigger an initial event on creation. This can be useful for setting default values on controls.
 
+	```swift
+	Task {
+		for await (foo, bar) in Defaults.updates([.foo, .bar]) {
+			print("Values changed:", foo, bar)
+		}
+	}
+	```
+	*/
+	public static func updates<each Value: Serializable>(
+		_ keys: repeat Key<each Value>,
+		initial: Bool = true
+	) -> AsyncStream<(repeat each Value)> {
+		.init { continuation in
+			func getCurrentValues() -> (repeat each Value) {
+				(repeat self[each keys])
+			}
+
+			var observations = [DefaultsObservation]()
+
+			if initial {
+				continuation.yield(getCurrentValues())
+			}
+
+			for key in repeat (each keys) {
+				let observation = DefaultsObservation(object: key.suite, key: key.name) { _, _  in
+					continuation.yield(getCurrentValues())
+				}
+
+				observation.start(options: [])
+				observations.append(observation)
+			}
+
+			let immutableObservations = observations
+
+			continuation.onTermination = { _ in
+				// `invalidate()` should be thread-safe, but it is not in practice.
+				DispatchQueue.main.async {
+					for observation in immutableObservations {
+						observation.invalidate()
+					}
+				}
+			}
+		}
+	}
+
+	// We still keep this as it can be useful to pass a dynamic array of keys.
+	/**
+	Observe updates to multiple stored values without receiving the values.
+
+	- Parameter keys: The keys to observe updates from.
+	- Parameter initial: Trigger an initial event on creation. This can be useful for setting default values on controls.
+
 	```swift
 	Task {
 		for await _ in Defaults.updates([.foo, .bar]) {
@@ -307,7 +358,7 @@ extension Defaults {
 	}
 	```
 
-	- Note: This does not include which of the values changed. Use ``Defaults/updates(_:initial:)-88orv`` if you need that. You could use [`merge`](https://github.com/apple/swift-async-algorithms/blob/main/Sources/AsyncAlgorithms/AsyncAlgorithms.docc/Guides/Merge.md) to merge them into a single sequence.
+	- Note: This does not include which of the values changed. Use ``Defaults/updates(_:initial:)-l03o`` if you need that.
 	*/
 	public static func updates(
 		_ keys: [_AnyKey],

Sources/Defaults/Documentation.docc/Documentation.md

@@ -52,6 +52,7 @@ typealias Default = _Default
 ### Methods
 
 - ``Defaults/updates(_:initial:)-88orv``
+- ``Defaults/updates(_:initial:)-l03o``
 - ``Defaults/updates(_:initial:)-1mqkb``
 - ``Defaults/reset(_:)-7jv5v``
 - ``Defaults/reset(_:)-7es1e``

Tests/DefaultsTests/DefaultsTests.swift

@@ -581,6 +581,34 @@ final class DefaultsTests {
 		let count = await counter.count
 		#expect(count == 2)
 	}
+
+	@available(iOS 16.0, macOS 13.0, tvOS 16.0, watchOS 9.0, visionOS 1.0, *)
+	@Test
+	func testUpdatesMultipleKeysVariadic() async {
+		let key1 = Defaults.Key<Bool>("updatesMultipleKeyVariadic1", default: false, suite: suite_)
+		let key2 = Defaults.Key<Bool>("updatesMultipleKeyVariadic2", default: false, suite: suite_)
+		let counter = Counter()
+
+		async let waiter: Void = {
+			for await (_, _) in Defaults.updates(key1, key2, initial: false) {
+				await counter.increment()
+
+				if await counter.count == 2 {
+					break
+				}
+			}
+		}()
+
+		try? await Task.sleep(for: .seconds(0.1))
+
+		Defaults[key1] = true
+		Defaults[key2] = true
+
+		await waiter
+
+		let count = await counter.count
+		#expect(count == 2)
+	}
 }
 
 actor Counter {