at:tutorial:objects
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at:tutorial:objects [2007/07/10 22:21] – changed tvcutsem | at:tutorial:objects [2007/07/27 10:15] – added tvcutsem | ||
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Line 94: | Line 94: | ||
def z := 0; | def z := 0; | ||
def sumOfSquares() { | def sumOfSquares() { | ||
- | super^sumOfSquares() + z*z | + | super^sumOfSquares() + z*z; |
}; | }; | ||
} | } | ||
Line 159: | Line 159: | ||
def Enumerable := object: { | def Enumerable := object: { | ||
def collect: closure { | def collect: closure { | ||
- | def c := clone: | + | def c := self.new([]); |
self.each: { |v| | self.each: { |v| | ||
- | c.add(closure(v)) | + | c.add(closure(v)); |
}; | }; | ||
+ | c; | ||
}; | }; | ||
}; | }; | ||
def Array := object: { | def Array := object: { | ||
def elements := []; | def elements := []; | ||
- | def init() { ... }; | + | def init(a) { elements := a; }; |
+ | def add(v) { elements := elements + [v]; self }; | ||
def collect: closure { | def collect: closure { | ||
Enumerable^collect: | Enumerable^collect: | ||
}; | }; | ||
def each: clo { | def each: clo { | ||
- | 1.to: elements.length do: { |i| | + | 1.to: elements.length |
- | clo(elements[i]) | + | clo(elements[i]); |
}; | }; | ||
}; | }; | ||
Line 181: | Line 183: | ||
A message sent to an object using the '' | A message sent to an object using the '' | ||
- | Of course, the example above is a bit contrived: we could have just assigned '' | + | < |
+ | > 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 '' | Having described the semantics of '' | ||
Line 202: | Line 214: | ||
===== 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; |
- | >> | + | >> |
< | < | ||
</ | </ | ||
+ | |||
+ | ===== Uniform Access ===== | ||
+ | |||
+ | AmbientTalk inherits from languages like Self, Eiffel and Ruby the property that field access is made indistinguishable from invoking a nullary method. This property is often referred to as the [[Wp> | ||
+ | |||
+ | < | ||
+ | def o := object: { | ||
+ | def x := 5 | ||
+ | }; | ||
+ | > o.x | ||
+ | >> 5 | ||
+ | o := object: { | ||
+ | def x() { 5 } | ||
+ | }; | ||
+ | > o.x | ||
+ | >> 5 | ||
+ | </ | ||
+ | |||
+ | Hence, the general rule is that '' | ||
+ | |||
+ | < | ||
+ | def o := object: { | ||
+ | def x := 5 | ||
+ | def xPlus1() { x + 1 } | ||
+ | }; | ||
+ | > o.xPlus1 | ||
+ | >> 6 | ||
+ | o := object: { | ||
+ | def x() { 5 } | ||
+ | def xPlus1() { x + 1 } | ||
+ | }; | ||
+ | > o.xPlus1 | ||
+ | >> 6 | ||
+ | </ | ||
+ | |||
+ | Note that the variable lookup '' | ||
+ | |||
+ | ==== UAP and closures ==== | ||
+ | |||
+ | One may wonder how the uniform access principle interacts with closures. That is, if '' | ||
+ | |||
+ | < | ||
+ | def o := object: { | ||
+ | def x := { 5 } | ||
+ | }; | ||
+ | > o.x | ||
+ | >> < | ||
+ | </ | ||
+ | |||
+ | The rationale is that '' | ||
+ | |||
+ | < | ||
+ | > o.x() | ||
+ | >> 5 | ||
+ | </ | ||
+ | |||
+ | When explicitly // | ||
+ | |||
+ | ==== UAP and Assignment ==== | ||
+ | |||
+ | In order to uphold the uniform access principle, special care is required with respect to assignment. If clients should be fully able to abstract over the implementation of slots as either fields or accessor methods, it should be possible to unify field assignment with mutator invocation. In AmbientTalk, | ||
+ | |||
+ | < | ||
+ | def realField := 5; | ||
+ | def o := object: { | ||
+ | def virtualField() { realField }; | ||
+ | def virtualField: | ||
+ | }; | ||
+ | > o.virtualField | ||
+ | >> 5 | ||
+ | > o.virtualField := 3 // interpreted as o.virtualField: | ||
+ | >> 3 | ||
+ | </ | ||
+ | |||
+ | In essence, assigning the field of an object is treated as a message send triggering a mutator method. Here's a more useful example of virtual fields: | ||
+ | |||
+ | < | ||
+ | def time := object: { | ||
+ | def seconds := 60; | ||
+ | // a field implicitly represents an accessor method seconds() | ||
+ | // and a mutator method seconds: | ||
+ | |||
+ | def minutes() { (seconds / 60) }; | ||
+ | def hours() | ||
+ | |||
+ | def minutes: | ||
+ | seconds := mins * 60; mins | ||
+ | }; | ||
+ | def hours: | ||
+ | seconds := hours * 3600; hours | ||
+ | }; | ||
+ | }; | ||
+ | > time.minutes | ||
+ | >> 1 | ||
+ | > time.hours := 1 | ||
+ | >> 1 | ||
+ | > time.seconds | ||
+ | >> 3600 | ||
+ | > time.seconds := 180 | ||
+ | > time.minutes | ||
+ | >> 2 | ||
+ | </ | ||
+ | |||
+ | If no mutator method is defined, the field assignment will fail with a '' | ||
+ | |||
+ | < | ||
+ | AmbientTalk has no direct notion of '' | ||
+ | </ | ||
+ | |||
+ | The uniform access principle for assignments equally holds for lexically visible methods. In other words, the code '' | ||
+ | |||
+ | <note warning> | ||
+ | The parser currently does not support the explicit invocation of a mutator as a method or function (as in '' | ||
+ | </ |
at/tutorial/objects.txt · Last modified: 2013/05/17 20:23 by tvcutsem