at:tutorial:objects
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at:tutorial:objects [2007/07/09 21:25] – explained tvcutsem | at:tutorial:objects [2007/07/10 22:27] – changed tvcutsem | ||
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</ | </ | ||
- | Every object understands the message '' | + | Every object understands the message '' |
< | < | ||
Line 86: | Line 86: | ||
Delegation implies that, if a message is sent to an object, but that object has no definition for the message' | 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, | + | AmbientTalk distinguishes between **two kinds** of delegation relationships, |
+ | |||
+ | An **IS-A** delegation relationship between two objects signifies that the child object " | ||
< | < | ||
Line 93: | Line 95: | ||
def sumOfSquares() { | def sumOfSquares() { | ||
super^sumOfSquares() + z*z | super^sumOfSquares() + z*z | ||
- | } | + | }; |
} | } | ||
</ | </ | ||
- | In this example, '' | + | In this example, '' |
- | These relationships define two different semantics for clonning child objects. Whereas clonning a **IS-A** child also clones its parent, **SHARE-A** | + | 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 |
+ | The following code shows how to extend objects with a **SHARES-A** delegation relationship. It uses the '' | ||
- | {{:at:tutorial:isaversussharea.png|:at: | + | < |
+ | def Collection | ||
+ | def elements | ||
+ | | ||
+ | } | ||
+ | </ | ||
+ | In this code example, the '' | ||
- | The following code shows how to extend objects with a **IS-A** | + | The **IS-A** |
+ | {{: | ||
+ | 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. | ||
- | The following code shows how to extend | + | ===== Delegation and Dynamic Inheritance ===== |
+ | |||
+ | In AmbientTalk, | ||
+ | |||
+ | Because '' | ||
< | < | ||
- | > def point3D | + | def openConnection |
- | def z := 0; | + | def send(msg) { ... }; |
- | def sumOfSquares() { | + | }; |
- | super^sumOfSquares() + z*z | + | def closedConnection |
- | } | + | def send(msg) { ... }; |
- | } | + | }; |
+ | def connection := object: { | ||
+ | | ||
+ | super := closedConnection; | ||
+ | }; | ||
+ | def open() { | ||
+ | | ||
+ | | ||
+ | | ||
+ | super := closedConnection; | ||
+ | }; | ||
+ | } | ||
</ | </ | ||
- | ===== Delegation | + | In the above example, the '' |
- | The parent of an object is bound to a field named '' | + | |
+ | < | ||
+ | In AmbientTalk, | ||
+ | </ | ||
+ | |||
+ | ===== First-class | ||
+ | |||
+ | AmbientTalk provides | ||
< | < | ||
- | > def openConnection | + | def Enumerable |
- | > def closedConnection := object: {...}; | + | def collect: closure |
- | > def connection | + | def c := clone: self; |
- | | + | |
- | | + | |
}; | }; | ||
- | | + | }; |
- | | + | }; |
+ | def Array := object: { | ||
+ | def elements := []; | ||
+ | | ||
+ | def collect: closure { | ||
+ | Enumerable^collect: | ||
+ | }; | ||
+ | def each: clo { | ||
+ | 1.to: elements.length do: { |i| | ||
+ | clo(elements[i]) | ||
}; | }; | ||
- | } | + | }; |
+ | }; | ||
</ | </ | ||
- | <note important> | + | A message sent to an object using the '' |
- | In AmbientTalk, '' | + | |
- | </ | + | |
- | ===== First-class delegation ===== | + | Of course, the example above is a bit contrived: we could have just assigned |
- | AmbientTalk provides an explicit delegation operator | + | |
+ | Having described the semantics | ||
< | < | ||
- | > def point3D | + | def Point3D |
- | def z := 0; | + | def z := 0; |
- | def init(aX, aY, aZ) { | + | def init(aX, aY, aZ) { |
- | super^init(aX, | + | super^init(aX, |
- | z := aZ; | + | z := aZ; |
- | }; | + | }; |
- | } | + | }; |
</ | </ | ||
- | |||
- | A message sent to an object using the '' | ||
<note warning> | <note warning> | ||
- | The delegation operator | + | AmbientTalk, |
+ | |||
+ | Keep in mind, however, that '' | ||
</ | </ | ||
===== Encapsulation ===== | ===== Encapsulation ===== | ||
- | In AmbientTalk, all fields and methods are " | + | |
+ | AmbientTalk | ||
< | < | ||
- | > def makeObject(hidden) { | + | def makeBankAccount(balance) { |
- | object: { | + | object: { |
- | def foo() { /* use hidden */ } | + | def deposit(amnt) { |
- | } | + | balance := balance + amnt; |
+ | " | ||
+ | }; | ||
} | } | ||
+ | } | ||
</ | </ | ||
- | Due to the encapsulation of this object the following | + | Because |
< | < | ||
- | > makeObject(5).hidden; | + | > makeBankAccount(100).balance; |
- | >> | + | >> |
< | < | ||
</ | </ |
at/tutorial/objects.txt · Last modified: 2013/05/17 20:23 by tvcutsem