From: Joel VanderWerf <joelvanderwerf@...>
Date: 2010-10-21T08:18:22+09:00
Subject: Re: First Law of Classes

On 10/20/2010 03:37 PM, Mike Stephens wrote:
> If you saw a class without persistent data, would you be suspicious?

Maybe, but there are good uses:

1. instance as unique token

   STATUS_OK = Object.new
   STATUS_FAIL = Object.new

   result =
     begin
       # try something
     rescue
       STATUS_FAIL
     else
       STATUS_OK
     end

2. flyweight pattern

   class PseudoRandom
     def initialize
       # set up seed, etc.
     end

     def next
       # get number from seed
     end
   end

   class Random
     def next
       # get number from /dev/urandom
     end
   end

   # This method accepts *either* of the above classes.
   # Even though Random has no state, it supports the same
   # interface as Pseudorandom.
   def get3 cl
     seq = cl.new
     [seq.next; seq.next; seq.next]
   end