未定义的方法[]为无：NilClass在红宝石哈希

Question

我有一个哈希包括：

flow = ["a", "b", "c"] 
h = [{"case_id"=>1, "a"=>{"x"=>"text", "option"=>"..." },"b"=>{"report"=>"text", "option"=>"..." } ,"c"=>{"y"=>"text", "option"=>"..." }},{"case_id"=>2, "a"=>{"x"=>"text", "option"=>"..." },"b"=>{"report"=>"text", "option"=>"..." } ,"c"=>{"y"=>"text", "option"=>"..." }}] 
@case = 0 
@report = "" 
flow.each do |step| 
    if h[@case][step]['report'] 
    @report = h[@case][step]['report'] 
    end 
end 

控制台使我有以下错误：

NoMethodError in MainController#index 
undefined method `[]' for nil:NilClass 

为什么？在之前的程序中，但使用红宝石187，没有问题。但现在，红宝石193，给出了这个错误。

Answer 1

flow = ["a", "b", "c"] 
h = { "a"=>{"x"=>"text", "option"=>"..." },"b"=>{"report"=>"text", "option"=>"..." } ,"c"=>{"y"=>"text", "option"=>"..." }} 
flow.each do |f| 
    if h[f]['report'] 
    #something 
    end 
end 

Ruby有通过枚举类

http://www.ruby-doc.org/core-1.9.3/Array.html#method-i-each

Answer 2

直到h或h[a]为nil，您都不会收到错误。请正确更新您的问题。