在Ruby中可以自动初始化多维哈希数组，就像在PHP中一样？

问题描述

 我很习惯在PHP中使用多维数组工作，在这里我可以分配和初始化一个哈希值。未设置（$ A）; //只是为了表明没有变量$ 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？或者我需要首先初始化所有维度，然后分配值。是否有可能定义一个高级哈希来实现我需要的功能？你会怎么做？

---

更新

除Douglas提出的解决方案（见下文）外，我还找到了，其中BrianSchröäer提出了对 Hash 类的扩展：

  class AutoHash<哈希
 def初始化（* args）
 super（）
 @update，@update_index = args [0] [：update]，args [0] [：update_key]除非args.empty？ 
结束
 
 def []（k）
如果self.has_key？k 
 super（k）
 else 
 AutoHash.new ：update => self，：update_key => k）
 end 
 end 
 
 def [] =（k，v）
 @update [@update_index ] = self如果@update和@update_index 
 super 
 end 
 end 
  

它允许解决问题，当只需要项目值时创建缺失的哈希项目，例如 a ['key'] 。

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其他参考

3. 试试看
试试看这：



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

如果该键不存在，则块的结果将被用作默认值。在这种情况下，默认值也是使用散列作为其默认值的散列。




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';

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?

---

Update

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

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'].

---

Some additional references

1. ruby hash autovivification (facets)
2. http://trevoke.net/blog/2009/11/06/auto-vivifying-hashes-in-ruby/
3. http://www.eecs.harvard.edu/~cduan/technical/ruby/ycombinator.shtml
解决方案

Try this:

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

a = hash_with_default_hash

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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