# File lib/Getopt/Declare.rb, line 307
     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