Differences

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--- at:tutorial:objects [2007/06/29 08:43] – jorge
+++ at:tutorial:objects [2007/06/29 13:31] – jorge
@@ Line 18: / Line 18: @@
     def sumOfSquares() { x*x + y*y };
   }
->><object:439658>
 </code>
@@ Line 27: / Line 26: @@
 </note>
-In the example above, the state of the ''point'' object is composed of ''x'' and ''y'' fields and its behaviour corresponds to the ''init'' and ''sumOfSquares'' methods.
+In the example above, the state of the ''point'' object is composed of ''x'' and ''y'' fields while its behaviour corresponds to the ''init'' and ''sumOfSquares'' methods.
 ===== Sending messages =====
@@ Line 46: / Line 45: @@
 <code>
 > def anotherPoint := point.new(2,3)
->><object:13393187>
 </code>
 Every object understands the message ''new'', which creates a clone (a shallow copy) of the receiver object and initializes the clone by invoking its ''init'' method with the arguments that were passed to new (''aX'' and ''aY'' in the example of the ''point'' object). Hence, the ''init'' method plays the role of “constructor” for AmbientTalk objects. AmbientTalk’s object instantiation protocol closely corresponds to class instantiation in class-based languages, except that the new object is a clone of an existing object, rather than an empty object allocated from a class.
-===== Delegation and Dynamic Inheritance =====
 ===== 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 child-parent 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.
+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 z := 0;
+    def sumofsquares() {
+      super.sumofsquares() + z*z
+    }
+  }
+</code>
+The following code shows how to extend objects with a **SHARE-A** relationship. It uses the ''share: with:'' language construct.
+<code>
+> def point3D := share: point with: {
+    def z := 0;
+    def sumofsquares() {
+      super.sumofsquares() + z*z
+    }
+  }
+</code>
+===== Delegation and dynamic inheritance =====
+An object's dynamic parent is the object bound to the field named ''super''
 ===== First-class Delegation =====