Yah boo, attr accessor with magic and history. Feel free to use it to cheat if you are a king-sized idiot who doesn't want to learn!

attr_accessor_with_history.rb

class Class
  def attr_accessor_with_history(attr_name)
    attr_reader attr_name
        
    class_eval %Q{
      # Create the attribute's history getter
      def #{attr_name}_history
        @#{attr_name}_history ||= [nil]
      end
      
      # Create the attribute's setter
      def #{attr_name}=(value)
        #{attr_name}_history << value
        
        @#{attr_name} = value  
      end
    }
  end
end

# Run the file with "rspec attr_accessor_with_history.rb" to run the tests.
if defined? RSpec
  class Foo
    attr_accessor_with_history :foo
    attr_accessor_with_history "bar"
  end
 
  describe Class do
    let(:subject) { Foo.new }
    let(:another_subject) { Foo.new }
    
    describe "reader" do
      it "should initially be nil" do
        subject.bar.should eq nil
      end
      
      it "should give the latest value" do
        subject.bar = 1
        subject.bar = 2
        subject.bar.should eq 2
      end
      
      it "should maintain separate values for each attribute" do
        subject.bar = 1
        subject.foo = 2
        subject.bar.should eq 1        
      end
      
      it "should maintain separate values for each object" do
        subject.bar = 1
        another_subject.bar = 2
        subject.bar.should eq 1        
      end
    end
    
    describe "*_history" do
      it "should initially record the value of nil" do
        subject.bar_history.should eq [nil]
      end
      
      it "should record new values in the history" do
        subject.bar = 1
        subject.bar = 2
        subject.bar_history.should eq [nil, 1, 2]
      end
      
      it "should maintain separate histories for each attribute" do
        subject.bar = 1
        subject.foo = 2
        subject.bar_history.should eq [nil, 1]        
      end
      
      it "should maintain separate histories for each object" do
        subject.bar = 1
        another_subject.bar = 2
        subject.bar_history.should eq [nil, 1]        
      end
    end
  end
end



=begin
class Class
  def attr_accessor_with_history(attr_name)
    attr_name = attr_name.to_s   # make sure it's a string
    attr_reader attr_name        # create the attribute's getter
    attr_reader attr_name+"_history" # create bar_history getter
    class_eval "your code here, use %Q for multiline strings"
  end
end

class Foo
  attr_accessor_with_history :bar
end

f = Foo.new()
puts f
f.bar = 1
f.bar = 2
f.bar_history
=end