apply_mapping

# File activesupport/lib/active_support/multibyte/chars.rb, line 663
        def apply_mapping(mapping) #:nodoc:
          chars(self.class.u_unpack(@wrapped_string).map do |codepoint|
            cp = UCD.codepoints[codepoint]
            if cp and (ncp = cp.send(mapping)) and ncp > 0
              ncp
            else
              codepoint
            end
          end.pack('U*'))
        end