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--- at:tutorial:objects [2007/06/29 13:19]
jorge
+++ at:tutorial:objects [2013/05/17 20:23]
tvcutsem updated
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-In this section, we explain how the object-oriented programming paradigm is implemented in AmbientTalk.
-===== Objects, fields and methods =====
-In AmbientTalk, objects are not instantiated from
-classes. Rather, they are either created ex-nihilo or by cloning
-and adapting existing objects, like prototypes in the SELF programming language. The definition of such a prototypical object contains a number of fields and methods that represent the object's state and behaviour respectively.
-The following code illustrates the ex-nihilo creation of an object:
-<code>
-> def point := object: {
-    def x := 0;
-    def y := 0;
-    def init(aX,aY) {
-      x := aX;
-      y := aY;
-    };
-    def sumOfSquares() { x*x + y*y };
-  }
-</code>
-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.
-<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 while its behaviour corresponds to the ''init'' and ''sumOfSquares'' methods.
-===== Sending messages =====
-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>
-> point.x
->>2
-> point.sumOfSquares()
->>13
-</code>
-This code shows two messages sent to the ''point'' 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 created [[objects#Objects,_fields_and_methods|ex-nihilo]] or by cloning and adapting an existing object. The code below shows the instatiation of a new ''point'' object by using the cloning semantics.
-<code>
-> def anotherPoint := point.new(2,3)
-</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 =====
-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 defines two different semantics for clonning child objects. Clonning a **IS-A** child also clones its parent whereas **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 cloning =====
-===== First-class Delegation =====
-===== Encapsulation =====

Ambient-Oriented Programming

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