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--- at:tutorial:objects [2007/07/09 21:13] – rewrote tvcutsem
+++ at:tutorial:objects [2007/07/09 21:25] – explained tvcutsem
@@ Line 80: / Line 80: @@
 </code>
-===== Delegation and cloning =====
+===== Delegation and Cloning =====
-AmbientTalk features object inheritance or delegation. By means of delegation, an object can reuse and extend the defintion of another establishing a parent-child relationship. We identify two kinds of delegation relationships: **IS-A** and **SHARE-A**. These relationships define two different semantics for clonning child objects. Whereas clonning a **IS-A** child also clones its parent, **SHARE-A** child shares the parent of the cloned object (see the figure below).
+In order to support code reuse and modular extensions between objects, AmbientTalk features //delegation// (also known as object-based inheritance). By means of delegation, an object can reuse and extend the fields and methods of another object by establishing a so-called "parent-child" or "delegate-delegator" relationship.
-{{:at:tutorial:isaversussharea.png|:at:tutorial:isaversussharea.png}}
+Delegation implies that, if a message is sent to an object, but that object has no definition for the message's selector, then the message is //delegated// to a designated object (often called the //parent// or //delegate//). What is important to note here is that "delegating" a message is not the same as simply "forwarding" the message to the other object: delegating a message leaves the ''self'' pseudovariable unchanged to the //original// receiver of the message.
+AmbientTalk distinguishes between **two kinds** of delegation relationships,**IS-A** and **SHARES-A**, each denoting a different kind of object extension. An **IS-A** delegation relationship between two objects signifies that the child object "is-a" kind of parent object, with the implicit assumption that such a child object cannot exist without its parent. As an example, consider the following code (don't worry about the meaning of ''^'' yet):
-The following code shows how to extend objects with a **IS-A** relationship. It uses the ''extend: with:'' language construct.
 <code>
-> def point3D := extend: point with: {
+def Point3D := extend: Point with: {
-    def z := 0;
+  def z := 0;
-    def sumOfSquares() {
+  def sumOfSquares() {
-      super^sumOfSquares() + z*z
+    super^sumOfSquares() + z*z
-    }
   }
+}
 </code>
+In this example, ''Point3D'' delegates
+These relationships define two different semantics for clonning child objects. Whereas clonning a **IS-A** child also clones its parent, **SHARE-A** child shares the parent of the cloned object (see the figure below).
+{{:at:tutorial:isaversussharea.png|:at:tutorial:isaversussharea.png}}
+The following code shows how to extend objects with a **IS-A** relationship. It uses the ''extend: with:'' language construct.
 The following code shows how to extend objects with a **SHARE-A** relationship. It uses the ''share: with:'' language construct.