class Module

def mattr_writer(*syms)
  options = syms.extract_options!
  syms.each do |sym|
    raise NameError.new('invalid attribute name') unless sym =~ /^[_A-Za-z]\w*$/
    class_eval(<<-EOS, __FILE__, __LINE__ + 1)
      def self.#{sym}=(obj)
        @@#{sym} = obj
      end
    EOS
    unless options[:instance_writer] == false || options[:instance_accessor] == false
      class_eval(<<-EOS, __FILE__, __LINE__ + 1)
        def #{sym}=(obj)
          @@#{sym} = obj
        end
      EOS
    end
  end
end