# File lib/earthquake/id_var.rb, line 14
      def initialize(vars = "aa".."zz", prefix = "$")
        unless Range === vars and String === vars.first
          raise ArgumentError, "vars should be a Range of String"
        end
        @vars = vars
        @var = @vars.last.dup
        @table = ActiveSupport::Cache::MemoryStore.new
        @prefix = prefix
      end