at:tutorial:reflection
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at:tutorial:reflection [2007/07/18 16:32] – jorge | at:tutorial:reflection [2010/11/16 15:59] – fixed tvcutsem | ||
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[[wp> | [[wp> | ||
- | The reflective model of AmbientTalk is based on [[http:// | + | The reflective model of AmbientTalk is based on [[http:// |
===== Mirrors ===== | ===== Mirrors ===== | ||
- | AmbientTalk uses a mirror-based architecture to provide reflective access to its objects. The basic principle of a mirror-based architecture is that all reflective facilities are encapsulated in a mirror object which provides reflective access to precisely one object, its reflectee. Moreover, the mirror of the object is not directly accessible as a slot of the object. Instead, a separate factory must be used to create mirrors, which allows the program to hand out different mirrors | + | |
+ | As we have mentioned in the introduction, | ||
+ | |||
+ | A convenience primitive exists that allows AmbientTalk programmers to acquire a mirror on an object without explicitly having to consult the mirror | ||
+ | |||
+ | Once a mirror has been created, it can be used to inspect | ||
< | < | ||
- | def baseObject | + | def Point := object: { |
- | def field := nil; | + | def x := 0; |
- | def canonicalMethod() { nil }; | + | def y := 0; |
- | def keyworded: arg1 method: arg2 { nil }; | + | def distanceToOrigin() |
}; | }; | ||
- | def mirror := reflect: | + | def p := Point.new(2, |
- | def slots := mirror.listSlots(); | + | // request a mirror |
- | slots.each: { | slot | system.println(slot) }; | + | > def mirrorOnP |
+ | >>< | ||
+ | |||
+ | > | ||
+ | >> | ||
</ | </ | ||
- | The code excerpt presented above uses the mirror to // | + | The code excerpt presented above uses the mirror to // |
- | In addition to allowing a program to reason about the structure of its objects, mirrors can also be used to write operations such as message sending in a first-class manner. The following example uses this power to invoke | + | {{: |
+ | |||
+ | The code excerpt below shows how one can add and remove slots to and from an object, and how one can explicitly access values and invoke | ||
< | < | ||
- | def invokeUserMethod(object) { | + | // let's add a z coordinate to our point |
- | def userInput | + | def [zaccessor, zmutator] |
- | // This example assumes that the user typed a single symbol | + | // we only add the accessor, so the slot is read-only |
- | (reflect: object).invoke(object, userInput, []); | + | mirrorOnP.addSlot(zaccessor); |
- | }; | + | // let's test it: |
+ | > p.z | ||
+ | >> 0 | ||
+ | // we can also read slots reflectively: | ||
+ | > def x : | ||
+ | >> < | ||
+ | > x() | ||
+ | >> 2 | ||
+ | // and we can also invoke methods reflectively: | ||
+ | > mirrorOnP.invoke(p, lobby.at.lang.values.createInvocation(`distanceToOrigin, | ||
+ | >> 3.605551275463989 | ||
+ | // finally, we can remove slots... | ||
+ | > mirrorOnP.removeSlot(`z); | ||
</ | </ | ||
- | This part of the tutorial has provided a basic feeling of how AmbientTalk' | + | The following example contains the core of a unit testing framework by showing how to select all zero-argument methods of an object whose name starts with '' |
+ | |||
+ | < | ||
+ | >def isTestMethod(meth) { | ||
+ | | ||
+ | { meth.parameters.length == 0 } }; | ||
+ | >>< | ||
+ | >def retainTestMethods(obj) { | ||
+ | | ||
+ | | ||
+ | >>< | ||
+ | >def runTest(obj) { | ||
+ | | ||
+ | | ||
+ | >>< | ||
+ | > | ||
+ | ok | ||
+ | >> | ||
+ | </ | ||
+ | |||
+ | This part of the tutorial has provided a basic feeling of how AmbientTalk' | ||
+ | |||
+ | < | ||
+ | defaultMirror.listSlots.map: | ||
+ | </ | ||
+ | |||
+ | |||
+ | A complete overview of all meta-operations will be presented | ||
===== Mirages ===== | ===== Mirages ===== | ||
- | Extending the AmbientTalk core language | + | |
+ | Extending the AmbientTalk core language | ||
+ | |||
+ | As a simple example, we show how to trace all method calls made on an object. The first step is to define | ||
< | < | ||
- | def dynamicExtensionMirror | + | def createTracingMirror(baseObject) { |
- | def doesNotUnderstand(selector) { | + | extend: defaultMirror.new(baseObject) with: { |
- | system.println(" | + | def invoke(slf, invocation) { |
- | system.println(" | + | system.println(" |
- | def input := system.readln(); | + | super^invoke(slf, invocation); |
- | if: !( "" | + | } |
- | def definition := read: input; | + | } |
- | eval: definition in: base; | + | |
- | } else: { | + | |
- | super^doesNotUnderstand(selector); | + | |
- | }; | + | |
- | }; | + | |
} | } | ||
</ | </ | ||
- | This mirror | + | The primitive '' |
+ | |||
+ | < | ||
+ | def TracingMirror := mirror: { | ||
+ | def invoke(slf, invocation) { | ||
+ | system.println(" | ||
+ | super^invoke(slf, | ||
+ | } | ||
+ | } | ||
+ | </ | ||
+ | |||
+ | The next step is to create objects | ||
< | < | ||
def mirage := object: { | def mirage := object: { | ||
- | def m() { self.x | + | def foo() { 42 }; |
- | } mirroredBy: | + | } mirroredBy:{ |emptyBase| createTracingMirror(emptyBase) }; |
</ | </ | ||
- | When invoking | + | In the code above, |
- | < | + | Another alternative |
- | Note that the use of '' | + | |
- | </ | + | |
- | Whereas the example provided above may seem a little contrived, the reflective capabilities of AmbientTalk allow it to be extended with many abstraction relating to distributed computing for mobile ad hoc networks (AmbientTalk' | + | < |
+ | def mirage := object: { | ||
+ | def foo() { 42 }; | ||
+ | } mirroredBy: TracingMirror; | ||
+ | </ | ||
+ | |||
+ | The AmbientTalk VM will then call '' | ||
+ | |||
+ | When invoking the method '' | ||
+ | |||
+ | < | ||
+ | > mirage.foo(); | ||
+ | invoked foo on < | ||
+ | >> 42 | ||
+ | </ | ||
+ | |||
+ | The picture below gives an overview of the different objects involved in the actor. | ||
+ | |||
+ | {{: | ||
+ | |||
+ | Whereas the example provided above may seem a little contrived, the reflective capabilities of AmbientTalk allow it to be extended with many abstraction relating to distributed computing for mobile ad hoc networks (AmbientTalk' | ||
===== The Metaobject Protocol ===== | ===== The Metaobject Protocol ===== | ||
- | The Meta-Object Protocol of AmbientTalk can be divided into a series of independent protocols. Whereas the full semantics and signature of the meta-methods can be found in the [[http://prog.vub.ac.be/ | + | The Meta-Object Protocol of AmbientTalk can be divided into a series of independent protocols. Whereas the full semantics and signature of the meta-methods can be found in the [[http://soft.vub.ac.be/ |
+ | |||
+ | The **Message Invocation Protocol** consists of methods to deal with both synchronous and asynchronous method invocation. It provides necessary hooks to intercept both the reception of asynchronous messages and the invocation of synchronous messages. Moreover, it provides a hook to intercept asynchronous messages being sent by the object, allowing the object to add additional metadata to the message. The '' | ||
- | The **Message Passing Protocol** consists of methods to deal with both synchronous and asynchronous message sending. It provides necessary hooks to intercept both the reception of asynchronous messages and the invocation of synchronous messages. Moreover, it provides a hook to intercept asynchronous messages being sent by the object, allowing the object to add additional metadata to the message. The '' | + | {{: |
- | The **Object | + | The **Object |
- | The **Slot Access and Modification Protocol** consists of operations which allow trapping both access and modification to slots. These operations are further refined based on whether they transitively search the dynamic or lexical parent chain. For instance, | + | The **Slot Access and Modification Protocol** consists of operations which allow trapping both dynamic |
- | The **Structural Access Protocol** consists of operations used list all available slots, get access to a first-class slot representation and to add new slots to an existing object. The '' | + | The **Structural Access Protocol** |
- | The **Instantiation Protocol** consists of the '' | + | The **Object |
The **Relational Testing Protocol** consists of the methods '' | The **Relational Testing Protocol** consists of the methods '' | ||
- | The **Type | + | The **Type |
The **Evaluation Protocol** ensures that any AmbientTalk object can be part of a parse tree, and therefore every object provides meaningful implementations of the '' | The **Evaluation Protocol** ensures that any AmbientTalk object can be part of a parse tree, and therefore every object provides meaningful implementations of the '' |
at/tutorial/reflection.txt · Last modified: 2010/11/16 16:32 by tvcutsem