Differences

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--- at:tutorial:objects [2007/07/02 11:18] – jorge
+++ at:tutorial:objects [2007/07/04 16:25] – jorge
@@ Line 48: / Line 48: @@
 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.
+AmbientTalk also provides a ''clone'' language contsruct which only creates a clone of the receiver object without calling the ''init'' method (as a matter of fact the ''new'' message desribed above does nothing more but invoking this construct and the ''init'' method subsequently).
+<code>
+> def clonedPoint := clone: point
+</code>
 ===== 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).
-{{:at:tutorial:isaversussharea.pdf|:at:tutorial:isaversussharea.pdf}}
+{{: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.
@@ Line 59: / Line 67: @@
 > def point3D := extend: point with: {
     def z := 0;
-    def sumofsquares() {
+    def sumOfSquares() {
-      super.sumofsquares() + z*z
+      super^sumOfSquares() + z*z
     }
   }
@@ Line 70: / Line 78: @@
 > def point3D := share: point with: {
     def z := 0;
-    def sumofsquares() {
+    def sumOfSquares() {
-      super.sumofsquares() + z*z
+      super^sumOfSquares() + z*z
     }
   }
@@ Line 80: / Line 88: @@
 <code>
-> def OpenConnection := object: {...};
+> def openConnection := object: {...};
-    def ClosedConnection := object: {...};
+> def closedConnection := object: {...};
-    def Connection := object: {
+> def connection := object: {
-      def open() {
+    def open() {
-        super := OpenConnection.new();
+      super := openConnection.new();
     };
     def close() {
-      super := ClosedConnection.new();
+      super := closedConnection.new();
+    };
+  }
+</code>
+<note important>
+In AmbientTalk, ''self'' and ''super'' indicate the current object and its parent respectively. While the former corresponds to a language keyword the latter is just a field name of the object.
+</note>
+===== First-class delegation =====
+AmbientTalk provides an explicit delegation operator ''^'' (the "caret" or "hat" symbol). The code below illustrates the use of the ''^'' operator in the implementation of the ''init'' method of the ''point3D'' object.
+<code>
+> def point3D := extend: point with: {
+    def z := 0;
+    def init(aX, aY, aZ) {
+      super^init(aX, aY);
+      z := aZ;
     };
   }
 </code>
-===== First-class Delegation =====
+A message sent to an object using the ''^'' symbol (e.g. to the parent object in the example above) will start the method lookup in this object (and its parents) and then execute the method body in the lexical scope of the message sender (''self'' is bound to the message sender).
+<note important>
+The ''^'' delegation operator does not have the same semantics as the ''.'' (dot) notation to send messages to ''super''. The ''.'' notation will not only start the method lookup in the object bound the ''super'' field but also bind the ''self'' pseudo variable to this object.
+</note>
 ===== Encapsulation =====