Ruby方法内部的数组操作 [英] Ruby array manipulation inside method

问题描述

以下，input_1进行了更改:

def method_1(a)
  a << "new value"
end

input_1 = []
method_1(input_1)
input_1 #=> ["new value"]

在以下情况中，input_2不变:

def method_2(a)
  a = ["new value"]
end

input_2 = []
method_2(input_2)
input_2 #=> []

为什么input_1更改而input_2不变?

推荐答案

通过一些简化，我们可以说Ruby中的变量是对值的引用.在您的情况下，变量a保存对数组的引用.

With a bit of simplification we can say that a variable in Ruby is a reference to a value. In your case variable a holds a reference to an array.

a <<(a.append)突变存储在变量a中的值.引用未更改，但值已更改.是method_1

a << (a.append) mutates the value stored in variable a. The reference is not changed, but the value did. It's the case of method_1

def method_1(a)
    a << "new value"
end

赋值=更改存储在变量中的引用-它开始指向另一个值.引用在传递给方法时被复制.因此，当您致电

Assignment = changes the reference stored in a variable - it starts to point to a different value. References are copied when passed to a method. Because of that when you call

def method_2(a)
    a = ["new value"]
end
input = []
method_2(a)

您只能更改存储在方法本地的a中的引用，而无需更改存储在input中的引用或该引用所指向的值(和[]的数组).

You only change a reference stored in a that is local to the method, without any change to the reference stored in input nor to the value (and array of []) that is pointed by this reference.

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