What's the variable scope within `class_eval` string?

Question

I am using class_eval to write code to be executed under the context of current class. In the following code, I want to add a counter for changes of attribute value

Answer 1

it is not about class_eval it is about @count. if you define this variable at class level it will be a class instance variable not an instance variable.

class Class
  def attr_count(attr_name)
    attr_name = attr_name.to_s
    attr_reader attr_name # create the attribute's getter
    class_eval %Q{
      def #{attr_name}= (attr_name)
        @attr_name = attr_name
        if @count
          @count += 1
        else
          @count = 1
        end
      end

      def #{attr_name}
        @attr_name
      end
    }
  end
end

class Foo
  attr_count :bar
end

f = Foo.new
f.bar = 1