为什么我的代码在使用散列符号而不是散列字符串时中断？ [英] Why does my code break when using a hash symbol, instead of a hash string?

问题描述

我有一个场景，当我尝试使用符号访问哈希键时，它不起作用，但是当我用字符串访问它时，它工作正常。这是我的理解，符号建议在字符串，所以我想清理我的脚本。我在脚本的其他地方使用了散列符号，这只是这种特定的场景不起作用。

以下是代码片段：

  account_params = {} 
 File.open（'file'，'r'）do | f | 
 f.each_line do | line | 
 hkey，hvalue = line.chomp.split（=）
 account_params [hkey] = hvalue 
 end 
 end 
 
 account_scope = account_params [ 范围] 
  

这可以起作用，但是如果我使用它不符合的符号，如下所示：

  account_scope = account_params [：范围] 
  

当我使用一个符号时：

 不能将nil转换为String （TypeError）
  

我不确定它是否重要，但是此特定哈希值的内容看起来像像这样：

  12345 / ABCD123 / 12345 
  

解决方案

您从文件中读取的关键字是字符串。实际上，您从文件中读取的所有内容都是一个字符串。如果你希望hash中的键是符号，你可以更新脚本来做这件事：

  account_params [hkey。 to_sym] = hvalue 
  

这会将hkey转换为符号，而不是使用字符串值。 / p>

Ruby提供了多种这些类型的方法，它们会将值强制为不同的类型。例如：to_i会将其转换为整数，to_f转换为浮点数，to_s将返回字符串值。

I have a scenario that when I try to access a hash key using a symbol it doesn't work, but when I access it with a string it works fine. It is my understanding that symbols are recommended over strings, so I am trying to clean my script. I am using hash symbols elsewhere in my script, it is just this specific scenario that does not work.

Here is the snippet:

account_params ={}
File.open('file', 'r') do |f|
  f.each_line do |line|
    hkey, hvalue = line.chomp.split("=")
    account_params[hkey] = hvalue
  end
end

account_scope = account_params["scope"]

This works, however if I use a symbol it doesn't, as shown below:

account_scope = account_params[:scope]

When I use a symbol I get:

can't convert nil into String (TypeError)

I am not sure if it matters, but the contents of this specific hash value looks something like this:

12345/ABCD123/12345

解决方案

The key you're reading in from the file is a string. In fact, everything you're reading in from the file is a string. If you want the keys in your hash to be symbols, you could update the script the do this instead:

account_params[hkey.to_sym] = hvalue

This will turn "hkey" into a symbol instead of using the string value.

Ruby provides a variety of these types of methods which will coerce the value into a different type. For instance: to_i will take it to an integer, to_f to a float, and to_s will take something back to a string value.

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