Merge pull request Kotlin#25 from thomaskempel/master

Add Example for Delegation Pattern

Author: hhariri

_data/examples.yml

@@ -36,5 +36,7 @@
   url: destructuring
 - title: Sealed Classes
   url: sealedClasses
+- title: Delegation Pattern
+  url: delegationPattern
 
 

_examples/delegationPattern.md

@@ -0,0 +1,41 @@
+---
+title: Delegation Pattern
+---
+
+<div class="sample" markdown="1">
+
+```kotlin
+interface SoundBehaviour {                                                          // 1
+    fun makeSound()
+}
+
+class ScreamBehavior(val n:String): SoundBehaviour {                                // 2
+    override fun makeSound() = println("${n.toUpperCase()} !!!")
+}
+
+class RockAndRollBehavior(val n:String): SoundBehaviour {
+    override fun makeSound() = println("I'm The King of Rock 'N' Roll: $n")    // 2
+}
+
+// Tom Araya is the "singer" of Slayer
+class TomAraya(n:String): SoundBehaviour by ScreamBehavior(n)                       // 3
+
+// You should know ;)
+class ElvisPresley(n:String): SoundBehaviour by RockAndRollBehavior(n)              // 3
+
+fun main(args: Array<String>) {
+    val tomAraya = TomAraya("Trash Metal!")
+    tomAraya.makeSound()                                                            // 4
+    val elvisPresley = ElvisPresley("Dancin' to the Jailhouse Rock.")
+    elvisPresley.makeSound()
+}
+```
+
+</div>
+
+In Kotlin it's easy to delegate method calls without any boilersplate.
+
+1.  The interface SoundBehaviour is defined. Later there will be one class that implements the method and another will also have the interface, but just delegates the method call.
+2.  The class ScreamBehavior and RockAndRollBehavior actually implement the method.
+3.  The class TomAraya and ElvisPresley just delegate the methods defined by the interface SoundBehaviour to the responsible implementation. But doesn't need any boilerplate to delegate the method call at all.
+4.  Call makeSound() on tomAraya of type TomAraya or elvisPresley of type ElvisPresley and it is delegated to the assiciated class