New observer implementation

src/main/kotlin/oop/Observer2/Observer.kt

@@ -0,0 +1,5 @@
+package oop.Observer2
+
+interface Observer<T> {
+  fun onChange(newValue: T)
+}

src/main/kotlin/oop/Observer2/Player.kt

@@ -0,0 +1,11 @@
+package oop.Observer2
+
+
+data class Player (val name: String,
+                   var currentCategory: String = "history") : Observer<String> {
+
+  override fun onChange(newValue: String) {
+    currentCategory = newValue
+    println("New category is $newValue")
+  }
+}

src/main/kotlin/oop/Observer2/RouletteObservable.kt

@@ -0,0 +1,20 @@
+package oop.Observer2
+
+import kotlin.properties.Delegates
+
+class RouletteObservable {
+
+  private val observers = mutableListOf<Observer<String>>()
+
+  var newCategory: String by Delegates.observable("") { _, _, new ->
+    observers.forEach { it.onChange(new) }
+  }
+
+  fun addObserver(observer: Observer<String>) {
+    observers.add(observer)
+  }
+
+  fun removeObserver(observer: Observer<String>) {
+    observers.remove(observer)
+  }
+}