From: Robert Klemme <shortcutter@...>
Date: 2009-12-20T00:58:13+09:00
Subject: Re: Encapsulating Information and Behavior without State

On 18.12.2009 17:12, Intransition wrote:
> 
> On Dec 17, 11:30 pm, Richard Conroy <richard.con...@gmail.com> wrote:
>> On Thu, Dec 17, 2009 at 5:15 PM, Intransition <transf...@gmail.com> wrote:
>>> So that's the idea. Getting back to the main question: What's the best
>>> way to encapsulate information and behavior when there is no state?
>> There's a bit of a contradiction here. To paraphrase what you said:
>>
>> What's the best
>> way to encapsulate "State" and behavior when there is no state?
>>
>> If there is unique information captured in objects (encapsulation) you have
>> state.
> 
> Sorry, by "information" I just meant constants (static information).
> 
>> You should look at modeling the system in a purely functional manner, but it
>> is hard
>> to see what you are attempting to do.
> 
> Maybe it will help if I explain how I got to this question. I started
> with a set of classes that all had one attribute, using a base class:
> 
>   class UnitType
>     attr :power
>     # ... methods ...
>   end
> 
> I had:
> 
>   class Meter < UnitType
>     # ... override methods ...
>   end
> 
>   class Second < UnitType
>     # ... override methods ...
>   end
> 
>   etc...
> 
> So each one was instantiated to track the power of a given unit. But
> then I realized that it would be better to couple the type and power
> via another class:
> 
>   class Unit
>     def initialize(unit_type, power)
>        @unit_type = unit_type
>        @power      = power
>     end
>   end
> 
> And remove the power attribute from the UnitType class. Thus I was
> left with a bunch of classes that had no state.

What's wrong with doing

   class UnitType
     class<<self
       attr_accessor :power
     end

     # ... methods ...

     def self.i_ve_got_the_power
       puts "#{self}'s power is #{power}"
     end
   end

   class Meter < UnitType
     self.power = 123
     # ... override methods ...
   end

   class Second < UnitType
     self.power = 456
     # ... override methods ...
   end

irb(main):022:0> Meter.i_ve_got_the_power
Meter's power is 123
=> nil
irb(main):023:0* Second.i_ve_got_the_power
Second's power is 456
=> nil

?

Kind regards

	robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/