at:tutorial:objects
Differences
This shows you the differences between two versions of the page.
Both sides previous revisionPrevious revisionNext revision | Previous revisionNext revisionBoth sides next revision | ||
at:tutorial:objects [2007/06/27 14:26] – jorge | at:tutorial:objects [2007/07/10 12:46] – fixed tvcutsem | ||
---|---|---|---|
Line 4: | Line 4: | ||
In AmbientTalk, | In AmbientTalk, | ||
classes. Rather, they are either created ex-nihilo or by cloning | classes. Rather, they are either created ex-nihilo or by cloning | ||
- | and adapting existing objects, | + | and adapting existing objects, |
The following code illustrates the ex-nihilo creation of an object: | The following code illustrates the ex-nihilo creation of an object: | ||
< | < | ||
- | > def Point := object: { | + | def Point := object: { |
- | def x := 0; | + | def x := 0; |
- | def y := 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 }; | + | def sumOfSquares() { x*x + y*y }; |
- | } | + | } |
- | >>< | + | |
</ | </ | ||
- | As all definitions in AmbientTalk, objects, fields and methods are defined using the **def** keyword. Fields are defined using a '' | + | The above code defines an // |
+ | |||
+ | In the example above, the state of the point object is composed of '' | ||
+ | |||
+ | < | ||
+ | As already explained in the [[at: | ||
+ | |||
+ | For Smalltalk/ | ||
+ | </ | ||
+ | |||
+ | ===== Sending messages ===== | ||
+ | In AmbientTalk, | ||
< | < | ||
- | > def aPoint := Point.new(2,3) | + | > Point.x |
- | >>< | + | >>0 |
+ | > Point.sumOfSquares() | ||
+ | >>0 | ||
</ | </ | ||
- | Every object understands | + | This code shows two messages sent to the point object |
- | <note important> | + | Note that the " |
- | AmbientTalk | + | |
+ | ===== Cloning and instantiation ===== | ||
+ | As noted above, | ||
+ | |||
+ | < | ||
+ | def anotherPoint := Point.new(2,3) | ||
+ | </ | ||
+ | |||
+ | Every object understands the message | ||
+ | |||
+ | < | ||
+ | > anotherPoint.x | ||
+ | >> 2 | ||
+ | > Point.x | ||
+ | >> 0 | ||
+ | > anotherPoint.x | ||
+ | >> nil | ||
+ | > Point.x | ||
+ | >> 0 | ||
+ | </ | ||
+ | |||
+ | < | ||
+ | AmbientTalk' | ||
</ | </ | ||
- | 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 | + | AmbientTalk |
- | ===== Sending messages ===== | + | < |
- | In AmbientTalk, | + | def clonedPoint := clone: Point |
+ | > clonedPoint.x | ||
+ | >> 0 | ||
+ | > clonedPoint.x := 2 | ||
+ | >> nil | ||
+ | > Point.x | ||
+ | >> 0 | ||
+ | </ | ||
- | access to | + | ===== Delegation and Cloning ===== |
- | access | + | In order to support code reuse and modular extensions between objects, AmbientTalk features // |
- | Object' | + | Delegation implies that, if a message is sent to an object, but that object has no definition for the message' |
+ | |||
+ | AmbientTalk distinguishes between **two kinds** of delegation relationships, | ||
+ | |||
+ | An **IS-A** delegation relationship between two objects signifies that the child object " | ||
< | < | ||
- | > aPoint.x | + | def Point3D := extend: Point with: { |
- | >>2 | + | def z := 0; |
- | > aPoint.sumOfSquares() | + | |
- | >>13 | + | |
+ | }; | ||
+ | } | ||
</ | </ | ||
+ | In this example, '' | ||
+ | A **SHARES-A** relationship between two objects signifies that an object only delegates to another object purely for reasons of code or state sharing. The delegation link has no other semantics, and conceptually both parent and child can exist without one another. | ||
- | ===== Cloning and instantiation ===== | + | The following code shows how to extend objects with a **SHARES-A** delegation relationship. It uses the '' |
+ | < | ||
+ | def Collection := share: Enumerable with: { | ||
+ | def elements := []; | ||
+ | ... | ||
+ | } | ||
+ | </ | ||
+ | In this code example, the '' | ||
- | ===== Delegation | + | The **IS-A** |
- | ===== Delegation and cloning ===== | + | {{: |
- | ===== First-class | + | This cloning semantics reinforces the semantics of **IS-A** as promoting a unique link between a parent and a child object. **IS-A** delegation most closely corresponds to class-based inheritance. |
+ | |||
+ | ===== Delegation and dynamic inheritance ===== | ||
+ | The parent of an object is bound to a field named '' | ||
+ | |||
+ | < | ||
+ | > def openConnection := object: {...}; | ||
+ | > def closedConnection := object: {...}; | ||
+ | > def connection := object: { | ||
+ | def open() { | ||
+ | super := openConnection.new(); | ||
+ | }; | ||
+ | def close() { | ||
+ | super := closedConnection.new(); | ||
+ | }; | ||
+ | } | ||
+ | </ | ||
+ | |||
+ | <note important> | ||
+ | In AmbientTalk, | ||
+ | </ | ||
+ | |||
+ | ===== First-class | ||
+ | AmbientTalk provides a special message-sending operator '' | ||
+ | |||
+ | < | ||
+ | def point3D := extend: point with: { | ||
+ | def z := 0; | ||
+ | def init(aX, aY, aZ) { | ||
+ | super^init(aX, | ||
+ | z := aZ; | ||
+ | }; | ||
+ | } | ||
+ | </ | ||
+ | |||
+ | A message sent to an object using the '' | ||
+ | |||
+ | <note warning> | ||
+ | The delegation operator does not have the same semantics as the dot notation. A message sent to '' | ||
+ | </ | ||
===== Encapsulation ===== | ===== Encapsulation ===== | ||
+ | In AmbientTalk, | ||
+ | < | ||
+ | > def makeObject(hidden) { | ||
+ | object: { | ||
+ | def foo() { /* use hidden */ } | ||
+ | } | ||
+ | } | ||
+ | </ | ||
+ | |||
+ | Due to the encapsulation of this object the following instruction fails: | ||
+ | |||
+ | < | ||
+ | > makeObject(5).hidden; | ||
+ | >> | ||
+ | < | ||
+ | </ |
at/tutorial/objects.txt · Last modified: 2013/05/17 20:23 by tvcutsem