在 Ruby 中是否可以像在 PHP 中那样自动初始化多维哈希数组? [英] Is auto-initialization of multi-dimensional hash array possible in Ruby, as it is in PHP?

问题描述

我习惯于在 PHP 中使用多维数组，我可以在其中分配和初始化散列

I am so used to work in PHP with multi-dimensional arrays, where I can assign and initialize a hash by

unset($a); // just to show that there is no variable $a
$a['settings']['system']['memory'] = '1 Gb';
$a['settings']['system']['disk space'] = '100 Gb';

有没有办法在 Ruby 中做类似的事情?或者我需要先初始化所有维度，然后再赋值.是否可以定义一个高级哈希来执行我需要的操作?你会怎么做?

Is there a way to do similar thing in Ruby? Or I need to initialize all dimensions first, and then to assign values. Is it possible to define an advanced Hash which will allow to do what I need? How would you do that?

更新

除了Douglas提出的解决方案(见下文)，我还找到了一个该主题的线程，其中 Brian Schröäer 提出了 Hash 类的扩展:

In addition to the solution proposed by Douglas (see below), I have found a thread on the subject, in which Brian Schröäer has proposed an extension for the Hash class:

class AutoHash < Hash
  def initialize(*args)
    super()
    @update, @update_index = args[0][:update], args[0][:update_key] unless args.empty?
  end

  def [](k)
    if self.has_key?k
      super(k)
    else
      AutoHash.new(:update => self, :update_key => k)
    end
  end

  def []=(k, v)
    @update[@update_index] = self if @update and @update_index
    super
  end
end

它可以解决在仅请求项目值时意外创建丢失的哈希项目时的问题，例如a['key'].

It allows to solve the problem when a missing hash item is undesirably created when the item value was only requested, e.g. a['key'].

一些额外的参考资料

1. ruby 哈希自动激活(方面)
2. http://trevoke.net/blog/2009/11/06/auto-vivifying-hashes-in-ruby/
3. http://www.eecs.harvard.edu/~cduan/technical/ruby/ycombinator.shtml

推荐答案

试试这个:

def hash_with_default_hash
    Hash.new { |hash, key| hash[key] = hash_with_default_hash }
end

a = hash_with_default_hash

如果键不存在，则块的结果将用作默认值.在这种情况下，默认值也是一个散列，它使用散列作为其默认值.

If the key doesn't exist, then the result of the block will be used as the default value. In this case, the default value is also a hash which uses hashes as its default values.

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