How to create new functions for String class in Ruby? -

i want check type of strings encounter:

class string     def is_i?         /\a[-+]?\d+\z/ === self     end      def is_path?         pn = pathname.new(self)         pn.directory?     end      end  def check(key)     puts case key     when is_i?         puts "could number"     when is_path?         puts "this path"     else         puts "ok"     end end 

when run check("1345425") following error:

undefined method `is_i?' main:object (nomethoderror) 

what should correct it?

you have defined functions on string instance, hence:

def check(key)     puts case          when key.is_i?            "could number"          when key.is_path?            "this path"          else            "ok"          end end 

or

def check(key)     puts case key          when ->(s) { s.is_i? }            "could number"          when ->(s) { s.is_path? }            "this path"          else            "ok"          end end 

upd please note removed superfluous subsequent calls puts.