红宝石错误：未定义的方法`casecmp”的零：NilClass

Question

我已（加入几调试行）以下代码：

红宝石：

re_dict = {} 
re_dict['state'] = 'pending' #set initial status to pending 
puts re_dict, re_dict.class.to_s 
puts re_dict['state'], re_dict['state'].class.to_s 
puts re_dict['state'].casecmp('pending') 
while re_dict['state'].casecmp('pending') == 0 do 
    stuff 
end 

输出

state: pending 
state class: String 
class compared to 'pending': 0 
Completed 500 Internal Server Error in 66ms 

NoMethodError (undefined method `casecmp' for nil:NilClass): 

这是什么造成的？我如何失去我的哈希值？

Answer 1

当您从re_dict哈希删除您while循环中'state'键这只会发生：

while re_dict['state'].casecmp('pending') == 0 do 
    puts re_dict 
    re_dict = {} 
end 
#=> {"state"=>"pending"} 
#=> NoMethodError: undefined method `casecmp' for nil:NilClass 

因为，关键'state'已不存在，调用re_dict['state']会给nil，这就是为什么你得到undefined method casecmp' for nil:NilClass