diff --git a/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/setting/Setting.kt b/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/setting/Setting.kt
index a765c9623..c79a836b6 100644
--- a/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/setting/Setting.kt
+++ b/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/setting/Setting.kt
@@ -17,7 +17,6 @@ import kotlin.internal.LowPriorityInOverloadResolution
 import kotlin.reflect.KProperty
 import kotlin.reflect.KType
 
-// TODO: 2020/6/21 move to JvmPlugin to inherit SettingStorage and CoroutineScope for saving
 // Shows public APIs such as deciding when to auto-save.
 abstract class Setting : SettingImpl() {
     operator fun <T> SerializerAwareValue<T>.provideDelegate(
diff --git a/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/setting/internal/CompositeValueImpl.kt b/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/setting/internal/CompositeValueImpl.kt
index a3e666b92..5b908f218 100644
--- a/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/setting/internal/CompositeValueImpl.kt
+++ b/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/setting/internal/CompositeValueImpl.kt
@@ -117,6 +117,8 @@ internal fun <K, V> Setting.createCompositeMapValueImpl(
     }
 }
 
+// TODO: 2020/6/24 在一个 Value 被删除后停止追踪其更新.
+
 internal abstract class CompositeMapValueImpl<K, V>(
     kToValue: (K) -> Value<K>, // should override onChanged
     vToValue: (V) -> Value<V> // should override onChanged
diff --git a/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/setting/internal/Setting.value composite impl.kt b/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/setting/internal/Setting.value composite impl.kt
index 12b26af65..c70db9e71 100644
--- a/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/setting/internal/Setting.value composite impl.kt	
+++ b/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/setting/internal/Setting.value composite impl.kt	
@@ -147,7 +147,14 @@ internal inline fun <R, T> T.cast(): R = this as R
  * Copied from kotlinx.serialization, modifications are marked with "/* mamoe modify */"
  * Copyright 2017-2020 JetBrains s.r.o.
  */
-@Suppress("UNCHECKED_CAST", "NO_REFLECTION_IN_CLASS_PATH", "UNSUPPORTED", "INVISIBLE_MEMBER", "INVISIBLE_REFERENCE")
+@Suppress(
+    "UNCHECKED_CAST",
+    "NO_REFLECTION_IN_CLASS_PATH",
+    "UNSUPPORTED",
+    "INVISIBLE_MEMBER",
+    "INVISIBLE_REFERENCE",
+    "IMPLICIT_CAST_TO_ANY"
+)
 @OptIn(ImplicitReflectionSerializer::class)
 internal fun serializerMirai(type: KType): KSerializer<Any?> {
     fun serializerByKTypeImpl(type: KType): KSerializer<Any> {
diff --git a/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/setting/internal/SettingImpl.kt b/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/setting/internal/SettingImpl.kt
index d71c7d590..8569ec27e 100644
--- a/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/setting/internal/SettingImpl.kt
+++ b/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/setting/internal/SettingImpl.kt
@@ -14,6 +14,7 @@ package net.mamoe.mirai.console.setting.internal
 import kotlinx.serialization.*
 import kotlinx.serialization.builtins.MapSerializer
 import kotlinx.serialization.builtins.serializer
+import net.mamoe.mirai.console.setting.Setting
 import net.mamoe.mirai.console.setting.Value
 import net.mamoe.yamlkt.YamlNullableDynamicSerializer
 import kotlin.reflect.KProperty
@@ -26,7 +27,6 @@ internal val KProperty<*>.serialName: String get() = this.findAnnotation<SerialN
  * - Reflection on Kotlin properties and Java fields
  * - Auto-saving
  */
-// TODO move to internal package.
 internal abstract class SettingImpl {
     internal fun findNodeInstance(name: String): Node<*>? = valueNodes.firstOrNull { it.serialName == name }
 
@@ -110,9 +110,7 @@ internal abstract class SettingImpl {
     /**
      * flatten
      */
-    internal fun onValueChanged(value: Value<*>) {
-        // TODO: 2020/6/22
-    }
+    abstract fun onValueChanged(value: Value<*>)
 
     companion object {
         private val settingUpdaterSerializerTypeArguments = arrayOf(String.serializer(), YamlNullableDynamicSerializer)
diff --git a/backend/mirai-console/src/test/kotlin/net/mamoe/mirai/console/setting/SettingTest.kt b/backend/mirai-console/src/test/kotlin/net/mamoe/mirai/console/setting/SettingTest.kt
index 6fce8dbb5..b3b2e51ed 100644
--- a/backend/mirai-console/src/test/kotlin/net/mamoe/mirai/console/setting/SettingTest.kt
+++ b/backend/mirai-console/src/test/kotlin/net/mamoe/mirai/console/setting/SettingTest.kt
@@ -20,8 +20,12 @@ internal class SettingTest {
 
     class MySetting : Setting() {
         var int by value(1)
-        val map by value(mapOf("" to ""))
-        val map2 by value(mutableMapOf("" to mutableMapOf("" to "")))
+        val map by value<MutableMap<String, String>>()
+        val map2 by value<MutableMap<String, MutableMap<String, String>>>()
+
+        override fun onValueChanged(value: Value<*>) {
+
+        }
     }
 
     @OptIn(UnstableDefault::class)
@@ -65,7 +69,7 @@ internal class SettingTest {
         val refBefore = setting.map
         fun reference() = refBefore
 
-        assertEquals(mapOf(), delegation()) // delegation
+        assertEquals(mutableMapOf(), delegation()) // delegation
 
         json.parse(
             setting.updaterSerializer, """