Berkeley SaaS class HW1 Part 5: advanced OOP with some metaprogramming

HW1_part5.rb

# advanced OOP with some metaprogramming

class Class
  def attr_accessor_with_history(attr_name)
    attr_name = attr_name.to_s
    # getter
    attr_reader attr_name
    attr_reader attr_name+"_history"
    # 为类动态添加方法
    class_eval %{     
        def #{attr_name}=(val)
          @#{attr_name} = val
          @#{attr_name}_history = [nil] if @#{attr_name}_history.nil?
          @#{attr_name}_history.push(val)
        end
        }
  end
end

class Foo 
 attr_accessor_with_history :bar 
end 

f = Foo.new 
f.bar = 1 
f.bar = 2 
p f.bar
p f.bar_history # => if your code works, should be [nil,1,2] 

thanks for showing me the correct way to do it but could you tell me where did you learn to do it? on the book of the course?