Publishers send the latest shared value for new subscriptions. Fixes #160. (#161)

Co-authored-by: Stephen Celis <[email protected]>

Author: kielgillard

Sources/Sharing/SharedPublisher.swift

@@ -15,9 +15,9 @@
     /// }
     /// ```
     public var publisher: some Publisher<Value, Never> {
-      box.subject
-        .handleEvents(receiveSubscription: { [box] _ in _ = box })
-        .prepend(wrappedValue)
+      Just<Void>(()).flatMap { _ in
+        box.subject.prepend(wrappedValue)
+      }
     }
   }
 
@@ -35,9 +35,9 @@
     /// }
     /// ```
     public var publisher: some Publisher<Value, Never> {
-      box.subject
-        .handleEvents(receiveSubscription: { [box] _ in _ = box })
-        .prepend(wrappedValue)
+      Just<Void>(()).flatMap { _ in
+        box.subject.prepend(wrappedValue)
+      }
     }
   }
 #endif

Tests/SharingTests/PublisherTests.swift

@@ -184,5 +184,34 @@
 
       #expect(counts.withLock(\.self) == [0, 1, 2, 3])
     }
+    
+    @Test func newSubscribersReceiveLatestValue() async throws {
+      @Shared(value: "initial") var value
+      let publisher = $value.publisher
+      
+      let firstSubscriberValues = Mutex<[String]>([])
+      
+      let firstCancellable = publisher.sink { completion in
+        Issue.record()
+      } receiveValue: { @Sendable value in
+        firstSubscriberValues.withLock { $0.append(value) }
+      }
+      defer { _ = firstCancellable }
+      
+      $value.withLock { $0 = "latest" }
+      #expect(firstSubscriberValues.withLock(\.self) == ["initial", "latest"])
+      
+      let secondSubscriberValues = Mutex<[String]>([])
+      
+      let secondCancellable = publisher.sink { completion in
+        Issue.record()
+      } receiveValue: { @Sendable value in
+        secondSubscriberValues.withLock { $0.append(value) }
+      }
+      defer { _ = secondCancellable }
+      
+      $value.withLock { $0 = "next" }
+      #expect(secondSubscriberValues.withLock(\.self) == ["latest", "next"])
+    }
   }
 #endif