how to access a class variable of outer class from inner class in ruby

问题

i have some code in Ruby here below:

class A
  @@lock = Monitor.new
  class B
    def method
      @@lock.synchronize
        puts "xxxxx"
      end
    end
  end
end    

after running it throws an error which said that below:

uninitialized class variable @@lock in A::B (NameError)

if i want to know how to access the outer class A's class variable @@lock from inner class B's method, how to do it? thank you in advance.

回答1:

The only way to access this class variable is via an accessor method

class A
   def self.lock
     @@lock ||= Monitor.new
   end

   class B
     def method
       A.lock.synchronize
         puts "xxxxx"
       end
     end
   end
 end

回答2:

I don't think you can without defining an accessor.

Class B is lexically scoped inside of A, so its real name is A::B and various other things are different.

But it's not a child or any other sort of derived class, so it doesn't actually have any special rights to see private or protected or otherwise local elements of A.

来源：https://stackoverflow.com/questions/4688588/how-to-access-a-class-variable-of-outer-class-from-inner-class-in-ruby