Ruby 在 Object 中查找类变量而不是特定类 [英] Ruby looks for class variable in the Object instead of specific class

问题描述

这部分有效:

 class Example1
   @@var1= "var1 in the Example1"
   def get_var1
     @@var1
   end
 end

 example1 = Example1.new
 example1.get_var1
 # => "var1 in the Example1"

但是如果我尝试使用 eigenclass:

but if I try eigenclass:

def example1.get_var1
  @@var1
end

example1.get_var1
# NameError: uninitialized class variable @@var1 in Object
# from (pry):128:in `get_var1'

Ruby 在 Object 中查找 @@var1 而不是 Example.

Ruby looks @@var1 in the Object instead of the Example.

我在 Ruby 1.9.3 和 2.0 中测试了这段代码，结果相同.

I have tested this code in the Ruby 1.9.3 and 2.0 with the same result.

为什么会这样?
第二件事，我们能不能把它关掉(这样 example.get_var1 就不会在 Object 中寻找类变量)?

Why does it happening?
The second thing, can we turn it off (so example.get_var1 won't look for class variables in the Object)?

推荐答案

看起来类变量查找的词法范围有点古怪.据我所知，因为你不在

It appears as though the lexical scope for class variable lookup is kind of wacky. As near as I can tell, because you're not inside the

class Example1
end

block，ruby 不会在您的类中查找 @@var，而是从 Object 中查找.如果你想从你的班级明确地得到它，你可以这样做:

block, ruby doesn't look up @@var in your class, but rather from Object. If you want it explicitly from your class, you can do:

def example1.get_var
    self.class.class_variable_get(:@@var1)
end

我偶然发现了 https://www.ruby-forum.com/topic/1228428 在寻找答案的同时.他们谈论的是 1.8.7，但它似乎也适用于更高版本.

I stumbled across https://www.ruby-forum.com/topic/1228428 while searching for the answer. They're talking about 1.8.7, but it appears to apply to later versions as well.

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