有人知道如何在CoffeeScript中成为私有的非静态成员吗?目前,我正在执行此操作,该操作仅使用以下划线开头的公共变量来阐明不应在类外使用它:
class Thing extends EventEmitter
constructor: (@_name) ->
getName: -> @_name
将变量放在类中使其成为静态成员,但是如何使其变为非静态呢?甚至有可能没有得到“幻想”?
Answers:
甚至有可能没有得到“幻想”?
可悲的是,你必须是看中。
class Thing extends EventEmitter
constructor: (name) ->
@getName = -> name
请记住,“这只是JavaScript。”
name
仅在构造函数闭包内部可见。看一下要点:gist.github.com/803810
@getName = -> name
似乎破坏了该getName
函数的任何继承。
getName
是公共的,name
只能从构造函数中访问,因此它实际上不是对象的“私有”。
类只是函数,因此它们创建范围。从外部看不到在此范围内定义的所有内容。
class Foo
# this will be our private method. it is invisible
# outside of the current scope
foo = -> "foo"
# this will be our public method.
# note that it is defined with ':' and not '='
# '=' creates a *local* variable
# : adds a property to the class prototype
bar: -> foo()
c = new Foo
# this will return "foo"
c.bar()
# this will crash
c.foo
coffeescript将其编译为以下内容:
(function() {
var Foo, c;
Foo = (function() {
var foo;
function Foo() {}
foo = function() {
return "foo";
};
Foo.prototype.bar = function() {
return foo();
};
return Foo;
})();
c = new Foo;
c.bar();
c.foo();
}).call(this);
foo.call(this)
,以便this
成为该函数的实例。这就是为什么尝试在JavaScript中模拟经典继承会变得麻烦的原因。
var
声明以使其阴影化。
我想展示一些更奇特的东西
class Thing extends EventEmitter
constructor: ( nm) ->
_name = nm
Object.defineProperty @, 'name',
get: ->
_name
set: (val) ->
_name = val
enumerable: true
configurable: true
现在你可以做
t = new Thing( 'Dropin')
# members can be accessed like properties with the protection from getter/setter functions!
t.name = 'Dragout'
console.log t.name
# no way to access the private member
console.log t._name
Vitaly的答案存在一个问题,那就是您无法定义要在作用域中唯一的变量,如果您以这种方式创建了一个私有名称,然后对其进行了更改,则该名称值将针对该类的每个实例而变化,所以有一种方法可以解决这个问题
# create a function that will pretend to be our class
MyClass = ->
# this has created a new scope
# define our private varibles
names = ['joe', 'jerry']
# the names array will be different for every single instance of the class
# so that solves our problem
# define our REAL class
class InnerMyClass
# test function
getNames: ->
return names;
# return new instance of our class
new InnerMyClass
除非您使用,否则从外部访问名称数组不是不可能的 getNames
测试一下
test = new MyClass;
tempNames = test.getNames()
tempNames # is ['joe', 'jerry']
# add a new value
tempNames.push 'john'
# now get the names again
newNames = test.getNames();
# the value of newNames is now
['joe', 'jerry', 'john']
# now to check a new instance has a new clean names array
newInstance = new MyClass
newInstance.getNames() # === ['joe', 'jerry']
# test should not be affected
test.getNames() # === ['joe', 'jerry', 'john']
编译的Javascript
var MyClass;
MyClass = function() {
var names;
names = ['joe', 'jerry'];
MyClass = (function() {
MyClass.name = 'MyClass';
function MyClass() {}
MyClass.prototype.getNames = function() {
return names;
};
return MyClass;
})();
return new MyClass;
};
这是一个利用此处其他答案的解决方案,以及https://stackoverflow.com/a/7579956/1484513。它将私有实例(非静态)变量存储在私有类(静态)数组中,并使用对象ID知道该数组的哪个元素包含属于每个实例的数据。
# Add IDs to classes.
(->
i = 1
Object.defineProperty Object.prototype, "__id", { writable:true }
Object.defineProperty Object.prototype, "_id", { get: -> @__id ?= i++ }
)()
class MyClass
# Private attribute storage.
__ = []
# Private class (static) variables.
_a = null
_b = null
# Public instance attributes.
c: null
# Private functions.
_getA = -> a
# Public methods.
getB: -> _b
getD: -> __[@._id].d
constructor: (a,b,@c,d) ->
_a = a
_b = b
# Private instance attributes.
__[@._id] = {d:d}
# Test
test1 = new MyClass 's', 't', 'u', 'v'
console.log 'test1', test1.getB(), test1.c, test1.getD() # test1 t u v
test2 = new MyClass 'W', 'X', 'Y', 'Z'
console.log 'test2', test2.getB(), test2.c, test2.getD() # test2 X Y Z
console.log 'test1', test1.getB(), test1.c, test1.getD() # test1 X u v
console.log test1.a # undefined
console.log test1._a # undefined
# Test sub-classes.
class AnotherClass extends MyClass
test1 = new AnotherClass 's', 't', 'u', 'v'
console.log 'test1', test1.getB(), test1.c, test1.getD() # test1 t u v
test2 = new AnotherClass 'W', 'X', 'Y', 'Z'
console.log 'test2', test2.getB(), test2.c, test2.getD() # test2 X Y Z
console.log 'test1', test1.getB(), test1.c, test1.getD() # test1 X u v
console.log test1.a # undefined
console.log test1._a # undefined
console.log test1.getA() # fatal error
这里是最好的文章中,我发现了大约设置public static members
,private static members
,public and private members
,和其他一些相关的东西。它涵盖了很多细节,并js
与coffee
比较。出于历史原因,这里是其中最好的代码示例:
# CoffeeScript
class Square
# private static variable
counter = 0
# private static method
countInstance = ->
counter++; return
# public static method
@instanceCount = ->
counter
constructor: (side) ->
countInstance()
# side is already a private variable,
# we define a private variable `self` to avoid evil `this`
self = this
# private method
logChange = ->
console.log "Side is set to #{side}"
# public methods
self.setSide = (v) ->
side = v
logChange()
self.area = ->
side * side
s1 = new Square(2)
console.log s1.area() # output 4
s2 = new Square(3)
console.log s2.area() # output 9
s2.setSide 4 # output Side is set to 4
console.log s2.area() # output 16
console.log Square.instanceCount() # output 2
这是在Coffeescript中声明私有,非静态成员的方法,以
供参考,您可以查看https://github.com/vhmh2005/jsClass
class Class
# private members
# note: '=' is used to define private members
# naming convention for private members is _camelCase
_privateProperty = 0
_privateMethod = (value) ->
_privateProperty = value
return
# example of _privateProperty set up in class constructor
constructor: (privateProperty, @publicProperty) ->
_privateProperty = privateProperty
咖啡脚本中的“类”导致基于原型的结果。因此,即使您使用私有变量,它也会在实例之间共享。你可以这样做:
EventEmitter = ->
privateName = ""
setName: (name) -> privateName = name
getName: -> privateName
.. 造成
emitter1 = new EventEmitter()
emitter1.setName 'Name1'
emitter2 = new EventEmitter()
emitter2.setName 'Name2'
console.log emitter1.getName() # 'Name1'
console.log emitter2.getName() # 'Name2'
但是要小心,将私有成员放在公共功能之前,因为coffee脚本会将公共功能作为对象返回。查看编译的Javascript:
EventEmitter = function() {
var privateName = "";
return {
setName: function(name) {
return privateName = name;
},
getName: function() {
return privateName;
}
};
};
由于coffee脚本会编译为JavaScript,因此拥有私有变量的唯一方法是通过闭包。
class Animal
foo = 2 # declare it inside the class so all prototypes share it through closure
constructor: (value) ->
foo = value
test: (meters) ->
alert foo
e = new Animal(5);
e.test() # 5
这将通过以下JavaScript进行编译:
var Animal, e;
Animal = (function() {
var foo; // closured by test and the constructor
foo = 2;
function Animal(value) {
foo = value;
}
Animal.prototype.test = function(meters) {
return alert(foo);
};
return Animal;
})();
e = new Animal(5);
e.test(); // 5
当然,这与使用闭包可以拥有的所有其他私有变量具有相同的局限性,例如,新添加的方法无法访问它们,因为它们不在同一范围内定义。
e = new Animal(5);f = new Animal(1);e.test()
提醒一个,我要五个。
使用CoffeeScript类很难做到这一点,因为它们使用Javascript构造函数模式创建类。
但是,您可以这样说:
callMe = (f) -> f()
extend = (a, b) -> a[m] = b[m] for m of b; a
class superclass
constructor: (@extra) ->
method: (x) -> alert "hello world! #{x}#{@extra}"
subclass = (args...) -> extend (new superclass args...), callMe ->
privateVar = 1
getter: -> privateVar
setter: (newVal) -> privateVar = newVal
method2: (x) -> @method "#{x} foo and "
instance = subclass 'bar'
instance.setter 123
instance2 = subclass 'baz'
instance2.setter 432
instance.method2 "#{instance.getter()} <-> #{instance2.getter()} ! also, "
alert "but: #{instance.privateVar} <-> #{instance2.privateVar}"
但是,您失去了CoffeeScript类的优越性,因为您不能通过其他方式(通过再次使用extend())从以这种方式创建的类中继承。instanceof将停止工作,以这种方式创建的objecs将消耗更多的内存。另外,您不得使用new和super关键字了。
关键是,每次实例化类时都必须创建闭包。纯CoffeeScript类中的成员闭包仅创建一次-即在构造类运行时“类型”时。