feat: add property delegation support for event declarations

Author: flemming-n-larsen

lib/common/src/main/kotlin/dev/robocode/tankroyale/common/Event.kt

@@ -12,6 +12,9 @@ import java.util.WeakHashMap
  * // Declare event
  * val onMyEvent = Event<MyEvent>()
  *
+ * // Declare event using property delegation (optional)
+ * val onMyDelegatedEvent by event<MyEvent>()
+ *
  * // Subscribe to event with an event handler to handle event when it occurs
  * onMyEvent.subscribe(this) { event -> handle(event) }
  *
@@ -121,6 +124,21 @@ open class Event<T> {
     }
 }
 
+/**
+ * Delegate for creating an [Event] instance using property delegation.
+ */
+class EventDelegate<T> {
+
+    private val event = Event<T>()
+
+    operator fun getValue(thisRef: Any?, property: kotlin.reflect.KProperty<*>): Event<T> = event
+}
+
+/**
+ * Creates an [EventDelegate] for property delegation: `val onEvent by event<T>()`.
+ */
+fun <T> event() = EventDelegate<T>()
+
 /**
  * Wrapper for subscribing with the once-flag using operator syntax.
  */

lib/common/src/test/kotlin/dev/robocode/tankroyale/common/EventTest.kt

@@ -67,6 +67,20 @@ class EventTest : FunSpec({
             result shouldBe listOf("test1")
         }
 
+        test("property delegation") {
+            val events = object {
+                val onMessage by event<String>()
+            }
+
+            val result = mutableListOf<String>()
+
+            events.onMessage.subscribe(this) { result.add(it) }
+            events.onMessage.fire("test")
+
+            (events.onMessage === events.onMessage) shouldBe true
+            result shouldBe listOf("test")
+        }
+
         test("subscribe once") {
             val event = Event<String>()
             val result = mutableListOf<String>()

openspec/changes/improve-event-system-kotlin/tasks.md

@@ -41,29 +41,29 @@
 
 ### 3.1 Event Delegate Implementation
 
-- [ ] 3.1.1 Create `EventDelegate<T>` class with `getValue()` operator
-- [ ] 3.1.2 Create `event()` factory function returning `EventDelegate<T>`
-- [ ] 3.1.3 Test property delegation in event object declarations
-- [ ] 3.1.4 Update KDoc with delegation examples
+- [x] 3.1.1 Create `EventDelegate<T>` class with `getValue()` operator
+- [x] 3.1.2 Create `event()` factory function returning `EventDelegate<T>`
+- [x] 3.1.3 Test property delegation in event object declarations
+- [x] 3.1.4 Update KDoc with delegation examples
 
 ### 3.2 Documentation Updates
 
-- [ ] 3.2.1 Document that delegation is optional (not required)
-- [ ] 3.2.2 Update Event.kt KDoc header with all usage patterns
+- [x] 3.2.1 Document that delegation is optional (not required)
+- [x] 3.2.2 Update Event.kt KDoc header with all usage patterns
 
 ## Phase 4: Testing and Validation
 
 ### 4.1 Existing Behavior Verification
 
-- [ ] 4.1.1 Run existing `EventTest.kt` without modifications
+- [x] 4.1.1 Run existing `EventTest.kt` without modifications
 - [ ] 4.1.2 Manual GUI smoke test — verify all event handlers work
 - [ ] 4.1.3 Verify `WebSocketClientEvents` work unchanged
-- [ ] 4.1.4 Test EDT.enqueue() extension function compatibility
+- [x] 4.1.4 Test EDT.enqueue() extension function compatibility
 
 ### 4.2 New Pattern Tests
 
-- [ ] 4.2.1 Add tests for operator `+=` and `-=` syntax
-- [ ] 4.2.2 Add tests for property delegation syntax
+- [x] 4.2.1 Add tests for operator `+=` and `-=` syntax
+- [x] 4.2.2 Add tests for property delegation syntax
 
 ## Phase 5: Documentation