apply_mapping

# File activesupport/lib/active_support/multibyte/unicode.rb, line 300
      def apply_mapping(string, mapping) #:nodoc:
        u_unpack(string).map do |codepoint|
          cp = database.codepoints[codepoint]
          if cp and (ncp = cp.send(mapping)) and ncp > 0
            ncp
          else
            codepoint
          end
        end.pack('U*')
      end