Add mutableCollectionState and docs.

src/jsMain/kotlin/nl/astraeus/komp/MutableCollectionStateDelegate.kt

@@ -0,0 +1,54 @@
+package nl.astraeus.komp
+
+inline fun <reified T> Komponent.mutableCollectionState(
+  initialValue: MutableCollection<T>
+): MutableCollection<T> = MutableCollectionStateDelegate(
+  this,
+  initialValue
+)
+
+class MutableCollectionStateDelegate<T>(
+  val komponent: Komponent,
+  val collection: MutableCollection<T>
+): MutableCollection<T> by collection {
+
+  override fun add(element: T): Boolean {
+    komponent.requestUpdate()
+
+    return collection.add(element)
+  }
+
+  override fun addAll(elements: Collection<T>): Boolean {
+    komponent.requestUpdate()
+
+    return collection.addAll(elements)
+  }
+
+  override fun clear() {
+    komponent.requestUpdate()
+
+    collection.clear()
+  }
+
+  // todo: return iterator wrapper to update at changes?
+  // override fun iterator(): MutableIterator<T> = collection.iterator()
+
+  override fun remove(element: T): Boolean {
+    komponent.requestUpdate()
+
+    return collection.remove(element)
+  }
+
+  override fun removeAll(elements: Collection<T>): Boolean {
+    komponent.requestUpdate()
+
+    return collection.removeAll(elements)
+  }
+
+  override fun retainAll(elements: Collection<T>): Boolean {
+    komponent.requestUpdate()
+
+    return collection.retainAll(elements)
+  }
+
+}

src/jsMain/kotlin/nl/astraeus/komp/State.kt

@@ -2,20 +2,41 @@ package nl.astraeus.komp
 
 import kotlin.reflect.KProperty
 
-class StateDelegate<T>(
-  val komponent: Komponent,
-  initialValue: T
-) {
-  var value: T = initialValue
+interface Delegate<T> {
 
   operator fun getValue(
     thisRef: Any?,
     property: KProperty<*>
+  ): T
+
+  operator fun setValue(
+    thisRef: Any?,
+    property: KProperty<*>,
+    value: T
+  )
+}
+
+
+open class StateDelegate<T>(
+  val komponent: Komponent,
+  initialValue: T
+) : Delegate<T> {
+  private var value: T = initialValue
+
+  init {
+    if (value is MutableCollection<*>) {
+      error("Use mutableList to create a collection!")
+    }
+  }
+
+  override operator fun getValue(
+    thisRef: Any?,
+    property: KProperty<*>
   ): T {
     return value
   }
 
-  operator fun setValue(
+  override operator fun setValue(
     thisRef: Any?,
     property: KProperty<*>,
     value: T
@@ -29,7 +50,7 @@ class StateDelegate<T>(
 
 inline fun <reified T> Komponent.state(
   initialValue: T
-): StateDelegate<T> = StateDelegate(
-  this,
-  initialValue
-)
+): Delegate<T> = StateDelegate(
+      this,
+      initialValue
+    )