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']
。
其他参考
- 试试看 试试看这:
- ruby hash autovivification (facets)
- http://trevoke.net/blog/2009/11/06/auto-vivifying-hashes-in-ruby/
- http://www.eecs.harvard.edu/~cduan/technical/ruby/ycombinator.shtml
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
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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