为什么数组是没有得到Ruby的修改？ [英] Why the array is not getting modified in Ruby?

问题描述

我试图code对IRB几行，然后我发现我不能修改一个新的数组返回从哈希的默认值。下面是一个IRB会议的更多详细信息，显示我的情况：

I was trying a few lines of code on IRB, and then I found that I could not modify a new array returned as a default value from a Hash. The following is an IRB session that shows in more details my situation:

a = Hash.new { Array.new }
#=> {}
a[2]
#=> []
a[2].push '2'
#=> ["2"]
a[2]
#=> []
a[2] = []
#=> []
a[2].push '2'
#=> ["2"]
a
#=> {2=>["2"]}
a[2].push '2'
#=> ["2", "2"]
a
#=> {2=>["2", "2"]}

为什么我不能修改一个不存在的键的默认值？

Why I cannot modify the default value of a nonexistent key?

推荐答案

的 哈希＃新 使用这样的：

The block form of Hash#new is used like this:

b = Hash.new {|hash, key| hash[key] = Array.new}
#=> {}
b[2]
#=> []
b[2].push('2')
#=> ["2"]
b[2]
#=> ["2"]
b[3]
#=> []
b[3].push('3')
#=> ["3"]
b[3]
#=> ["3"]

这篇关于为什么数组是没有得到Ruby的修改？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！