compare: equal?, Comparable module

check  whether  two objects are the same object

define how to compare

use Comparable module & define <=> method

the return value of method <=> ,  1, 0 , & -1 decides greater than, equal than, & less than

ex:

class Rabbit

     include Comparable 

     attr_accessor  :name

     def  <=> (other_rabbit)

          if  self.name <>

                  -1

          elsif  self.name > other_rabbit.name

                  1

          else

                  0

          end 

     end

end

if the thing to compare know how to compare, there is a shorter definition

ex:

def  <=> (other_rabbit)

       self.name<=> other_rabbit.name

end