at:tutorial:objects
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at:tutorial:objects [2007/07/10 12:39] – * tvcutsem | at:tutorial:objects [2007/07/19 07:59] – * tvcutsem | ||
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def z := 0; | def z := 0; | ||
def sumOfSquares() { | def sumOfSquares() { | ||
- | super^sumOfSquares() + z*z | + | super^sumOfSquares() + z*z; |
}; | }; | ||
} | } | ||
Line 101: | Line 101: | ||
In this example, '' | In this example, '' | ||
- | A **SHARES-A** relationship between two objects signifies that an object only delegates to another object purely for reasons of code sharing. The delegation link has no other semantics, and conceptually both parent and child can exist without one another. | + | 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. |
The following code shows how to extend objects with a **SHARES-A** delegation relationship. It uses the '' | The following code shows how to extend objects with a **SHARES-A** delegation relationship. It uses the '' | ||
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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. | 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 | + | ===== Delegation and Dynamic Inheritance |
- | The parent of an object is bound to a field named '' | + | |
+ | In AmbientTalk, | ||
+ | |||
+ | Because '' | ||
< | < | ||
- | > def openConnection := object: {...}; | + | def openConnection := object: |
- | > def closedConnection := object: {...}; | + | def send(msg) |
- | > def connection := object: { | + | }; |
- | def open() { | + | def closedConnection := object: |
- | super := openConnection.new(); | + | def send(msg) |
- | }; | + | }; |
- | def close() { | + | def connection := object: |
- | super := closedConnection.new(); | + | def init() |
- | }; | + | |
- | } | + | }; |
+ | | ||
+ | super := openConnection; | ||
+ | }; | ||
+ | def close() { | ||
+ | super := closedConnection; | ||
+ | }; | ||
+ | } | ||
</ | </ | ||
- | < | + | In the above example, the '' |
- | In AmbientTalk, | + | |
+ | < | ||
+ | In AmbientTalk, | ||
</ | </ | ||
- | ===== First-class | + | ===== First-class |
- | AmbientTalk provides | + | |
+ | AmbientTalk provides | ||
< | < | ||
- | > def point3D | + | def Enumerable |
- | def z := 0; | + | def collect: closure |
- | | + | def c := self.new([]); |
- | | + | |
- | z := aZ; | + | |
}; | }; | ||
- | | + | c; |
+ | | ||
+ | }; | ||
+ | def Array := object: { | ||
+ | def elements := []; | ||
+ | def init(a) { elements := a; }; | ||
+ | def add(v) { elements := elements + [v]; self }; | ||
+ | def collect: closure { | ||
+ | Enumerable^collect: | ||
+ | }; | ||
+ | def each: clo { | ||
+ | 1.to: elements.length + 1 do: { |i| | ||
+ | clo(elements[i]); | ||
+ | }; | ||
+ | }; | ||
+ | }; | ||
</ | </ | ||
- | A message sent to an object using the '' | + | A message sent to an object using the '' |
+ | |||
+ | < | ||
+ | > Array.add(1).add(2).add(3) | ||
+ | >> < | ||
+ | > def c := Array.collect: | ||
+ | >> < | ||
+ | > c.each: { |v| system.print(v)} | ||
+ | 234 | ||
+ | >> | ||
+ | </ | ||
+ | |||
+ | Of course, the example above is a bit contrived: we could have just assigned '' | ||
+ | |||
+ | Having described the semantics of '' | ||
+ | |||
+ | < | ||
+ | def Point3D := extend: Point with: { | ||
+ | def z := 0; | ||
+ | def init(aX, aY, aZ) { | ||
+ | super^init(aX, | ||
+ | z := aZ; | ||
+ | }; | ||
+ | }; | ||
+ | </ | ||
<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