CoffeeScript 中的动态类生成

2022-01-24 00:00:00 oop closures javascript coffeescript

在 CoffeeScript 中动态创建类以便稍后实例化它们的对象的最佳方法是什么?

What is the best way to dynamically create classes in CoffeeScript, in order to later instantiate objects of them?

我已经找到了实现它的方法，但我不确定是否有更好(或更简单)的方法来实现它.请让我知道您对我的代码的看法.

I have found ways to do it, but I am not sure if there is maybe an even better (or simpler) way to achieve it. Please let me know your thoughts on my code.

让我们从简单的非动态类开始:

Let's start with simple non-dynamic classes:

class Animal
  constructor: (@name) ->

  speak: ->
    alert "#{@name} says #{@sound}"

class Cat extends Animal
  constructor: (@name) ->
    @sound = "meow!"

garfield = new Cat "garfield"
garfield.speak()

果然，加菲猫喵喵叫！

但是现在我们要为更多的动物动态生成类，定义如下:

But now we want to dynamically generate classes for more animals, which are defined as follows:

animalDefinitions = [
    kind:  'Mouse'
    sound: 'eek!'
  ,
    kind:  'Lion'
    sound: 'roar!'
  ]

第一次天真的尝试失败了:

The first naive attempt fails:

for animal in animalDefinitions
  animal.class = class extends Animal
    constructor: (@name) ->
      @sound = animal.sound

mutant = new animalDefinitions[0].class "mutant"
mutant.speak()

我们刚刚创建的动物，mutant，应该是一只老鼠.但是，它说咆哮！这是因为 animal.sound 只有在我们实例化类时才会被评估.幸运的是，从 JavaScript 中我们知道了一种行之有效的方法来解决这个问题:闭包:

The animal we just created, mutant, should be a mouse. However, it says roar! This is because animal.sound only gets evaluated when we instantiate the class. Luckily, from JavaScript we know a proven way to solve this: a closure:

for animal in animalDefinitions
  makeClass = (sound) ->
    class extends Animal
      constructor: (@name) ->
        @sound = sound
  animal.class = makeClass(animal.sound)

mickey = new animalDefinitions[0].class "mickey"
mickey.speak()

simba = new animalDefinitions[1].class "simba"
simba.speak()

现在它可以正常工作了，米老鼠说 eek！狮子辛巴吼叫着！但它看起来已经有些复杂了.我想知道是否有更简单的方法来实现这个结果，也许是直接访问原型.还是我完全走错了路?

Now it works as desired, mickey mouse says eek! and simba the lion says roar! But it looks somewhat complicated already. I am wondering if there is an easier way to achieve this result, maybe by accessing the prototype directly. Or am I completely on the wrong track?

推荐答案

由于 sound 是 Animal 实例的默认值，您可以将其设置为类定义的属性:

Since sound is a default value for an Animal instance, you can set it as a property on class definition:

class Cat extends Animal
    sound: 'meow!'

garfield = new Cat "garfield"
garfield.speak() # "garfield says meow!"

然后

for animal in animalDefinitions
    animal.class = class extends Animal
        sound: animal.sound

mutant = new animalDefinitions[0].class "mutant"
mutant.speak() # "mutant says eek!"

如果你想让 sound 可以被覆盖，你可以这样做

If you want sound to be overridable, you can do

class Animal
    constructor: (@name, sound) ->
        @sound = sound if sound? 
    speak: ->
        console.log "#{@name} says #{@sound}"

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