克隆对象的变化值 [英] Change value of a cloned object

问题描述

我有了一个实例变量数组称为对象 my_array 。我通过声明它 attr_accessor中。

I have an object that has an instance variable array called my_array. I declare it via attr_accessor.

my_object.my_array = [1,2,3] # <= I don't know the max size of my_array(it can be dynamic)

我想创建一个 my_object 同一个对象，并填写了 my_array 只有一个元素。该元素内的值从 my_array 的元素的每个值（从 my_object ）。由于大小 my_array 是动态的，我想我需要通过来迭代每它。

I want to create the same object with my_object and fill its my_array with only one element. The value inside that element is each value from my_array's element (from my_object). Because the size of my_array is dynamic I suppose I need to iterate it via each.

下面是我的尝试：

my_object.my_array.each do |element|          # <= my_object is a special object
  new_object = nil unless new_object.nil?
  new_object = my_object.clone # <= I create new object with same class with my_object
  new_object.my_array.clear   # <= clear all element inside it.
  new_object.my_array.push(element)  # assign element value to the first element.
  # rest of code #
  new_object = nil 
end

迭代未正确迭代。 my_object.my_array 的大小为3，那么它应该迭代三次，但它不是，它只是迭代一次。我相信这是因为 new_object.my_array.clear ，但我克隆它从 my_object ，那么为什么会这样？

The iteration is not iterating properly. The size of my_object.my_array is 3, then it should iterating three times, but it's not, it's only iterating one time. I believe it's because of new_object.my_array.clear, but I cloned it from my_object, so why this happened?

推荐答案

的问题是，克隆将一个浅克隆，而不是一个深克隆。换句话说， my_array 是一个参考和克隆的实例引用相同的数组在内存中。试想一下：

The problem is, that clone will make a shallow clone, not a deep clone. In other words, my_array is a reference and the cloned instance references the same array in memory. Consider:

class MyClass
  attr_accessor :my_array
end

a = MyClass.new
a.my_array = [1, 2, 3]
a.my_array
#=> [1, 2, 3]

b = a.clone
b.my_array.push(4)
b.my_array
#=> [1, 2, 3, 4]
a.my_array              # also changed!
#=> [1, 2, 3, 4]

为了解决这个问题，你需要扩展 initialize_copy 方法也克隆数组：

In order to fix this, you need to extend the initialize_copy method to also clone the array:

class MyClass
  attr_accessor :my_array

  def initialize_copy(orig)
    super
    self.my_array = orig.my_array.clone
  end
end

a = MyClass.new
a.my_array = [1, 2, 3]
a.my_array
#=> [1, 2, 3]

b = a.clone
b.my_array.push(4)
b.my_array
#=> [1, 2, 3, 4]
a.my_array              # did not change, works as expected
#=> [1, 2, 3]

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