From: "Stephan Kämper" <Stephan.Kaemper@...>
Date: 2004-07-22T06:57:02+09:00
Subject: Referencing objects and program design

Hi all,

suppose I have some kind of object which holds 'object ids' referring to 
other objects, probably objects of its own class - or even itself.

Now adding an object to the list can be done (at least) in two ways: 
Pass an object to the method and let the method find out the object id, 
or pass the object id directly.

Now the following lines are just an example of what I'm thinking about 
(and it's certainly not thread safe among other things).

class Common_Base
   @@curr_oid = "aa"
   attr_reader :oid

   def initialize
     @oid = Common_Base.get_new_oid
   end

   def Common_Base.get_new_oid
     @@curr_oid = @@curr_oid.succ
   end
end

class Reference_List < Common_Base
   def initialize
     super
     @refs = []
   end

   def add_ref1( other )
     @refs << other.oid unless @refs.include? other.oid
   end

   def add_ref2( oid  )
     @refs << oid unless @refs.include? oid
   end
end

class Referenced < Common_Base
end

refl = Reference_List.new
ref  = Referenced.new

refl.add_ref1( ref )
p refl # -> <Reference_List:0x27862b0 @oid="ab", @refs=["ac"]>

refl.add_ref2( ref.oid )
p refl # -> <Reference_List:0x27862b0 @oid="ab", @refs=["ac"]>

refl.add_ref1( refl )
p refl # -> <Reference_List:0x27862b0 @oid="ab", @refs=["ac", "ab"]>


Now, for 'add_ref1' the method needs to know a bit more about the object 
to be added (needs to call the oid method of the added method), while 
'add_ref2' seems to put more work on the caller of the method (needs to 
ask for the added oid).
Anyway, right now using 'add_ref1' _seems_ to be more the 
'tell-the-other-guy' way, but I'm not too sure about that...
So, what's the better way to add a to-be-referenced object to the 
referencing object?

Any input is welcome. :-)

Happy rubying

Stephan

[1] See http://www.pragmaticprogrammer.com/articles/may_04_oo1.pdf for 
more on that.