memoized methods

    def self.cached_method(meth)
      eval <<-CODE
        def #{meth}_with_cache
          return @#{meth} if @#{meth}
          result = #{meth}_without_cache
          @#{meth} ||= result
        end
      CODE
      alias_method_chain meth, :cache
    end 

    def self.memoized_method(meth)
      eval <<-CODE
        def #{meth}_with_memoization(*args)
          @#{meth}_with_memoization ||= {}
          @#{meth}_with_memoization[args] ||= #{meth}_without_memoization(*args)
        end
      CODE
      alias_method_chain meth, :memoization
    end