gistfile1.rb

class << Object
  def my_aa(sym)
    define_method(sym) do
      instance_variable_get("@#{sym}")
    end

    define_method("#{sym}=") do |v|
      instance_variable_set("@#{sym}", v)
    end
  end
end

class Foo
  my_aa :alpha
end

a = Foo.new
a.alpha = "cow"
puts a.alpha