module Hamster::Immutable::ClassMethods

def memoize(*names)
  include MemoizeMethods unless include?(MemoizeMethods)
  names.each do |name|
    original_method = "__hamster_immutable_#{name}__"
    alias_method original_method, name
    class_eval <<-METHOD, __FILE__, __LINE__
      def #{name}
        if @__hamster_immutable_memory__.instance_variable_defined?(:@#{name})
          @__hamster_immutable_memory__.instance_variable_get(:@#{name})
        else
          @__hamster_immutable_memory__.instance_variable_set(:@#{name}, #{original_method})
        end
      end
    METHOD
  end
end