Ruby looks for class variable in the Object instead of specific class

问题

This part works:

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

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

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

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

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)?

回答1:

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 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

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.

来源：https://stackoverflow.com/questions/24510948/ruby-looks-for-class-variable-in-the-object-instead-of-specific-class