Ruby中的工厂方法 [英] Factory methods in Ruby

问题描述

让单个构造函数返回适当类型的对象的最巧妙，最类似于Ruby的方法是什么?

更具体地说，这是一个虚拟示例:假设我有两个类 Bike 和 Car ，它们是 Vehicle 的子类.我想要这个:

To be more specific, here's a dummy example: say I have two classes Bike and Car which subclass Vehicle. I want this:

Vehicle.new('mountain bike')  # returns Bike.new('mountain bike')
Vehicle.new('ferrari')        # returns Car.new('ferrari')

我在下面提出了一个解决方案，但是它使用了 allocate ，这似乎过于实现.还有什么其他方法，或者我真的可以吗?

I've proposed a solution below, but it uses allocate which seems way too implementation-heavy. What are some other approaches, or is mine actually ok?

推荐答案

如果我创建的工厂方法未被称为 ¹ new 或 initialize ，我想这并不能真正回答如何构造...构造函数..."的问题，但是我认为这就是我的解决方法……

If I make a factory method that is not called¹ new or initialize, I guess that doesn't really answer the question "how do I make a ... constructor ...", but I think that's how I would do it...

class Vehicle
  def Vehicle.factory vt
    { :Bike => Bike, :Car => Car }[vt].new
  end
end

class Bike < Vehicle
end

class Car < Vehicle
end

---

c = Vehicle.factory :Car
c.class.factory :Bike

---

^{1.在本示例示例中，调用方法 factory 确实非常有效，但是IRL您可能需要考虑 @AlexChaffee 在评论中的建议.}

---

^{1. Calling the method factory works really well in this instructional example but IRL you may want to consider @AlexChaffee's advice in the comments.}

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