Lazily start the controller when accessing the effects property

CHANGELOG.md

@@ -9,6 +9,7 @@
 - Update kotlinx.coroutines to `1.4.3`.
 - Remove kotlin as `api` dependency.
 - Remove `ControllerLog.default`.
+- Lazily start controller when accessing `Controller.effects` field (#26)
 
 ## `[0.13.1]` - 2020-09-13
 

control-core/src/main/kotlin/at/florianschuster/control/implementation.kt

@@ -142,6 +142,7 @@ internal class ControllerImplementation<Action, Mutation, State, Effect>(
         get() = if (stubEnabled) {
             stubbedEffectFlow.receiveAsFlow().cancellable()
         } else {
+            if (controllerStart is ControllerStart.Lazy) start()
             effectsChannel.receiveAsFlow().cancellable()
         }
 

control-core/src/test/kotlin/at/florianschuster/control/ImplementationTest.kt

@@ -256,6 +256,31 @@ internal class ImplementationTest {
         effects expect emissions(testEmissions)
     }
 
+    @Test
+    fun `controller is started lazily when only effects field is accessed`() {
+        val sut = ControllerImplementation<Int, Int, Int, String>(
+            scope = testCoroutineScope,
+            dispatcher = testCoroutineScope.defaultScopeDispatcher(),
+            controllerStart = ControllerStart.Lazy,
+            initialState = 0,
+            mutator = { action -> flowOf(action) },
+            reducer = { mutation, _ -> mutation },
+            actionsTransformer = { actions ->
+                merge(actions, flow {
+                    emitEffect("actionsTransformer started")
+                })
+            },
+            mutationsTransformer = { mutations -> mutations },
+            statesTransformer = { states -> states },
+            tag = "ImplementationTest.EffectController",
+            controllerLog = ControllerLog.None
+        )
+
+        val effects = sut.effects.testIn(testCoroutineScope)
+
+        effects expect emissions(listOf("actionsTransformer started"))
+    }
+
     @Test
     fun `effects are only received once collector`() {
         val sut = testCoroutineScope.createEffectTestController()