at:tutorial:objects
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at:tutorial:objects [2007/06/22 16:30] – jorge | at:tutorial:objects [2007/07/02 13:15] – jorge | ||
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- | We describe now how the object-oriented programming paradigm | + | In this section, we explain |
===== Objects, fields and methods ===== | ===== Objects, fields and methods ===== | ||
+ | In AmbientTalk, | ||
+ | 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' | ||
+ | |||
+ | The following code illustrates the ex-nihilo creation of an object: | ||
+ | |||
+ | < | ||
+ | > def point := object: { | ||
+ | def x := 0; | ||
+ | def y := 0; | ||
+ | def init(aX,aY) { | ||
+ | x := aX; | ||
+ | y := aY; | ||
+ | }; | ||
+ | def sumOfSquares() { x*x + y*y }; | ||
+ | } | ||
+ | </ | ||
+ | |||
+ | As all definitions in AmbientTalk, | ||
+ | |||
+ | <note important> | ||
+ | AmbientTalk not only supports traditional canonical syntax (e.g. '' | ||
+ | </ | ||
+ | |||
+ | In the example above, the state of the '' | ||
===== Sending messages ===== | ===== Sending messages ===== | ||
+ | In AmbientTalk, | ||
+ | |||
+ | < | ||
+ | > point.x | ||
+ | >>2 | ||
+ | > point.sumOfSquares() | ||
+ | >>13 | ||
+ | </ | ||
+ | |||
+ | This code shows two messages sent to the '' | ||
===== Cloning and instantiation ===== | ===== Cloning and instantiation ===== | ||
+ | As said before in this section, AmbientTalk objects are created [[objects# | ||
- | ===== Delegation | + | < |
+ | > def anotherPoint := point.new(2, | ||
+ | </ | ||
+ | |||
+ | Every object understands the message '' | ||
+ | |||
+ | AmbientTalk also provides a '' | ||
+ | |||
+ | < | ||
+ | > def clonedPoint := clone: point | ||
+ | </ | ||
===== Delegation and cloning ===== | ===== 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: | ||
- | ===== First-class | + | |
+ | {{: | ||
+ | |||
+ | |||
+ | The following code shows how to extend objects with a **IS-A** relationship. It uses the '' | ||
+ | |||
+ | < | ||
+ | > def point3D := extend: point with: { | ||
+ | def z := 0; | ||
+ | def sumofsquares() { | ||
+ | super.sumofsquares() + z*z | ||
+ | } | ||
+ | } | ||
+ | </ | ||
+ | |||
+ | The following code shows how to extend objects with a **SHARE-A** relationship. It uses the '' | ||
+ | |||
+ | < | ||
+ | > def point3D := share: point with: { | ||
+ | def z := 0; | ||
+ | def sumofsquares() { | ||
+ | super.sumofsquares() + z*z | ||
+ | } | ||
+ | } | ||
+ | </ | ||
+ | |||
+ | ===== 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(); | ||
+ | }; | ||
+ | } | ||
+ | </ | ||
+ | |||
+ | ===== First-class | ||
+ | AmbientTalk provides an explicit delegation operator '' | ||
+ | |||
+ | < | ||
+ | > def point3D := extend: point with: { | ||
+ | def z := 0; | ||
+ | def init(aX, aY, aZ) { | ||
+ | super^init(aX, | ||
+ | z := aZ; | ||
+ | } | ||
+ | } | ||
+ | </ | ||
===== 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