at:tutorial:objects
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at:tutorial:objects [2007/07/09 21:25] – explained tvcutsem | at:tutorial:objects [2007/07/10 12:42] – 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 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 ===== | ===== Delegation and dynamic inheritance ===== |
at/tutorial/objects.txt · Last modified: 2013/05/17 20:23 by tvcutsem