Json 这个nil键是如何进入散列的？

我试图实现一个json解析器。输入是

"{ \"key\": { \"foo\": \"bar\", \"hello\" : 100 } }"

我把它格式化成

"{key:{foo:bar,hello:100}}"

然后我将其标记化以获得如下数组

["{", "key", ":", "{", "foo", ":", "bar", ",", "hello", ":", "100", "}", "}"]

我可能也忽略了

，

。不管怎样，当我试图从那个数组构建ruby哈希时，我得到了这个结果

{nil=>{"key"=>{"foo"=>"bar", "hello"=>"100"}}}

我不知道这个

nil

是如何被用作键的。这是我用来构建散列的方法

def build_hash(arr)
  h = {}
  keys = []
  while arr.size > 0
    current_token = arr.shift
    if alpha?(current_token)
      if keys.empty? # that means a new key is to be expected
        keys << current_token
      else
        h[keys.pop] = current_token
      end
    elsif current_token == '}'
      # these shouldn't be any key left in the keys stack. if there is one, raise error
      # otherwise close the hash and return from method
      if not keys.empty?
        raise_invalid_format_error
      else
        return h
      end
    elsif current_token == ','
      # continue reading. new key will appear. There shouldn't be any key in keys[]
      raise_invalid_format_error unless keys.empty?
    elsif current_token == '{'
      # this means new hash is starting, nested. Should be a value to a key
      # recursive call, assign the result to the existing key
      h[keys.pop] = build_hash(arr)
    end
  end
  h
end

---

这是怎么回事

数组中的第一个标记将是

{

，这将贯穿到最后的

elsif

案例：

elsif current_token == '{'
  # this means new hash is starting, nested. Should be a value to a key
  # recursive call, assign the result to the existing key
  h[keys.pop] = ....

---

keys

数组是空的，因此

pop

返回

nil

，您将其用作哈希的键。

如我在注释中所述，只有在存在一个键时才弹出一个键：

def build_hash(arr)
  h = {}
  keys = []
  while arr.size > 0
    current_token = arr.shift
    if alpha?(current_token)
      if keys.empty? # that means a new key is to be expected
        keys << current_token
      else
        h[keys.pop] = current_token
      end
    elsif current_token == '}'
      # these shouldn't be any key left in the keys stack. if there is one, raise error
      # otherwise close the hash and return from method
      if not keys.empty?
        raise_invalid_format_error
      else
        return h
      end
    elsif current_token == ','
      # continue reading. new key will appear. There shouldn't be any key in keys[]
      raise_invalid_format_error unless keys.empty?
    elsif current_token == '{'
      # this means new hash is starting, nested. Should be a value to a key
      # recursive call, assign the result to the existing key
      if keys.any?
        h[keys.pop] = build_hash(arr)
      end
    end
  end
  h
end

def build_散列（arr）
h={}
键=[]
当arr.size>0时
当前_标记=arr.shift
如果alpha？（当前_令牌）
如果keys.empty？#这意味着需要一个新密钥
键为什么不简单：
require（'json'）；json.parse（{“key\”：{“foo\”：“bar\”，“hello\”：100}”）；
@JanZeiseweis是的，我知道。但是不使用任何库是一个必需的部分，第一个元素是“{”（我不确定alpha？在做什么）但是如果
alpha？
返回false，则跳到最后一个
elsif current_token='{'
，由于键是空的，
keys.pop
返回
nil
@JanZeiseweis噢。我忘记了
alpha？
，如果它是最后一个
elsif
中的字母或数字，则返回true，您应该只执行
h[keys.pop]=build_hash（arr）
只有当你的密钥不是空的；）现在就知道了。谢谢。投票结果：）我接受了简的答案，因为他第一次在评论中回答了这个问题。
def build_hash(arr)
  h = {}
  keys = []
  while arr.size > 0
    current_token = arr.shift
    if alpha?(current_token)
      if keys.empty? # that means a new key is to be expected
        keys << current_token
      else
        h[keys.pop] = current_token
      end
    elsif current_token == '}'
      # these shouldn't be any key left in the keys stack. if there is one, raise error
      # otherwise close the hash and return from method
      if not keys.empty?
        raise_invalid_format_error
      else
        return h
      end
    elsif current_token == ','
      # continue reading. new key will appear. There shouldn't be any key in keys[]
      raise_invalid_format_error unless keys.empty?
    elsif current_token == '{'
      # this means new hash is starting, nested. Should be a value to a key
      # recursive call, assign the result to the existing key
      if keys.any?
        h[keys.pop] = build_hash(arr)
      end
    end
  end
  h
end