Add self-type for Traits

Author: josephpconley

src/main/scala/stdlib/Traits.scala

@@ -100,5 +100,24 @@ object Traits extends FlatSpec with Matchers with org.scalaexercises.definitions
     myListener.isInstanceOf[Any] should be(res2)
     myListener.isInstanceOf[AnyRef] should be(res3)
   }
-
+  
+  /** Traits also can use self-types.  A self-type lists the required dependencies for mixing in the trait.  When mixing in the main trait, all self-type dependencies of that trait must also be mixed in, otherwise a compile-time error is thrown.
+   *  
+   * Also, the dependencies can't have identical method/property names or else you'll get an `illegal inheritance` error.
+   */
+  def selfTypeTraits(res0: Int){
+    trait B {
+      def bId = 2
+    }      
+    
+    trait A {
+      self: B =>
+      
+      def aId = 1
+    }
+    
+    //val a = new A  //***does not compile!!!***
+    val obj = new A with B
+    (obj.aId + obj.bId) should be(res0)
+  }
 }