Accessing Ruby Class Variables with class_eval and instance_eval

Question

I have the following:

class Test
    @@a = 10

    def show_a()
        puts \"a: #{@@a}\"
    end

    class << self
      @@b = \'40\'

      def show_b
         


        

Answer 1

Well, probably the best answer is "just because": the instance_eval in a nutshell creates some kind of singleton proc that is invoked with the binding of a given object. I agree that is sounds a bit strange, but it is what it is.

If you execute instance_eval with a string, you will even get a warning that your method tries to access class variable:

irb(main):038:0> Test.new.instance_eval "@@a"
(eval):1: warning: class variable access from toplevel singleton method
NameError: (eval):1:in `irb_binding': uninitialized class variable ...