Differences

This shows you the differences between two versions of the page.

--- at:tutorial:objects [2007/06/27 12:09] – jorge
+++ at:tutorial:objects [2007/06/29 08:31] – jorge
@@ Line 12: / Line 12: @@
     def x := 0;
     def y := 0;
-    def init(xCoord,yCoord) {
+    def init(aX,aY) {
-      x := xCoord;
+      x := aX;
-      y := yCoord;
+      y := aY;
     };
     def sumOfSquares() { x*x + y*y };
@@ Line 21: / Line 21: @@
 </code>
-As all definitions in AmbientTalk, objects are defined using the **def** keyword. 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.
+As all definitions in AmbientTalk, objects, fields and methods are defined using the **def** keyword. Fields are defined using a ''def name := value'' syntax while methods are defined using a ''name(parameters) {body}'' syntax.
-This object can be instantiated to create new points as follows:
+<note important>
+AmbientTalk not only supports traditional canonical syntax (e.g. ''o.m(a,b,c)'') but also keyworded syntax (e.g. ''o.at: key put: value'') for method definitions and message sends, as in SmallTalk.
+</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. This object can be instantiated to create new points as follows:
 <code>
-> def initialPoint := Point.new(0,0)
+> def aPoint := 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. 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. We further explain the semantics of object cloning in subsection [[objects#Delegation_and_cloning|Delegation and cloning]].
+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. We further explain the semantics of object cloning in subsection [[objects#Delegation_and_cloning|Delegation and cloning]].
 ===== Sending messages =====
-In AmbientTalk, computation is expressed in terms of object sending messages to one another.
+In AmbientTalk, computation is expressed in terms of objects sending messages to one another. Messages are used to invoke the fields and methods of the objects.
+<code>
+> aPoint.x
+>>2
+> aPoint.sumOfSquares()
+>>13
+</code>
+This code shows two messages sent to the ''aPoint'' object defined above in this section. The ''x'' message acts as an accessor for the ''x'' field. The ''sumOfSquares'' message selects the ''sumOfSquares'' method and evaluates its body.
 ===== Cloning and instantiation =====
+As said before in this section, AmbientTalk objects are [[objects#Objects,_fields_and_methods|created ex-nihilo]] or by cloning and adapting an existing object.