at:tutorial:objects
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at:tutorial:objects [2007/07/09 21:38] – rewrote tvcutsem | at:tutorial:objects [2007/07/10 22:04] – expanded tvcutsem | ||
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</ | </ | ||
- | Every object understands the message '' | + | Every object understands the message '' |
< | < | ||
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 '' | ||
Line 120: | Line 120: | ||
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 delegation ===== | ===== First-class delegation ===== | ||
- | AmbientTalk provides | + | AmbientTalk provides |
< | < | ||
- | > def point3D := extend: point with: { | + | def point3D := extend: point with: { |
- | 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 '' | + | A message sent to an object using the '' |
<note warning> | <note warning> |
at/tutorial/objects.txt · Last modified: 2013/05/17 20:23 by tvcutsem