# File lib/Getopt/Declare2.rb, line 310
      def conversion
        pat = @@stdtype[@type] ? @@stdtype[@type][:pattern] : ''
        [ @type, pat ].each { |t|
        case t
        when /^\:0?(\+)?i$/
         return '.to_i'
        when /^\:0?(\+)?n$/
         return '.to_f'
        end
        }
        return nil
      end