attrmethods.rb

module AttrMethods
  
  class << Object
    @@array_methods = {}
    @@hash_methods = {}
    def attr_array(*method_names)
      @@array_methods[self] = method_names
    end
    def attr_hash(*method_names)
      @@hash_methods[self] = method_names
    end
  end
  
  def initialize
  	gen_array_methods(self, @@array_methods[self.class]) if @@array_methods.has_key?(self.class)
  	gen_hash_methods(self, @@hash_methods[self.class])  if @@hash_methods.has_key?(self.class)
  	super()
  end

private

  def gen_array_methods(obj, method_names)
    method_names.each do |m|
        obj.instance_eval(<<-EOF, __FILE__, __LINE__)
          def #{m}(*args)
            @#{m} = args
          end   
        EOF
    end
  end

  def gen_hash_methods(obj, method_names)
    method_names.each do |m|
        obj.instance_eval(<<-EOF, __FILE__, __LINE__)
          def #{m}(*args)
            @#{m} = *args
          end   
        EOF
    end
  end
end

myclass.rb

class MyClass
  include AttrMethods

  attr_array :my_method
  attr_hash :method_two

  def put_array
    puts @my_method.join(" ")
  end

  def put_hash
    @method_two.each do |k,v|
      print "#{k} #{v} "
    end
  end
end

using myclass.rb

foo = MyClass.new

foo.my_method "this", "is", "an", "array"
foo.put_array #=> this is an array

foo.method_two "this" => "hash", "was" => "created", "with" => "metaprogramming"
foo.put_hash #=> this hash was created with metaprogramming