Question

我试图在我的CoffeeScript代码中创建一种全局的单例对象：

window.MyLib = 
  Foos: {}
  Bars: {}
  Client: ->
    @_client ||= (
      someVar = 'foo'
      new ExpensiveClient(someVar)
    )

# ...


MyLib.Client.performSomeAction()

但是，代码实际上要求我这样做：

MyLib.Client().performSomeAction()

如何解决实现惰性实例化的问题而无需使用括号将其作为函数调用？

更新：或者，如果有办法实现某种“方法缺失”，Client函数可以返回一个将责任委托给实际客户端的对象，但是只在需要时才实例化。

Answer 1

也许是这样的：

lazyGet = (obj, name, property) ->
  Object.defineProperty obj, name, get: property

window.MyLib = do ->
  @_client = null

  Foos: {}
  Bars: {}

  lazyGet this, 'Client', ->
    @_client ||= (
      someVar = 'foo'
      new ExpensiveClient someVar
    )

Answer 2

前几天我正在寻找一个单身人士，并在这个网站上找到了答案。 http://coffeescriptcookbook.com/chapters/design_patterns/singleton

这里的代码来自该网站，这可能是您正在寻找的

class Singleton
  # You can add statements inside the class definition
  # which helps establish private scope (due to closures)
  # instance is defined as null to force correct scope
  instance = null
  # Create a private class that we can initialize however
  # defined inside this scope to force the use of the
  # singleton class.
  class PrivateClass
    constructor: (@message) ->
    echo: -> @message
  # This is a static method used to either retrieve the
  # instance or create a new one.
  @get: (message) ->
    instance ?= new PrivateClass(message)

a = Singleton.get "Hello A"
a.echo() # => "Hello A"

b = Singleton.get "Hello B"
b.echo() # => "Hello A"

Singleton.instance # => undefined
a.instance # => undefined
Singleton.PrivateClass # => undefined

CoffeeScript：不使用括号进行惰性求值

2 个答案: