From: Dave Burt <dave@...>
Date: 2006-06-11T13:05:12+09:00
Subject: Re: Dynamic class change?

Mark Noworolski wrote:
> I have a stream I'm listening to that lots of similar things speak on, each of which also identifies itself with a unique MAC. 
> Say, I have 3 objects organized something like this:
> Class Nic
> End
> 
> Class Nic2 < Nic
> Etc.
> End
> 
> Class Nic3 < Nic2
> Etc.
> End
> 
> As time passes, when I hear a new MAC start talking, I dynamically create a corresponding object. So, if the first thing I hear is something a Nic says, a Nic object can spring into existence, ditto for Nic2, etc. So far, seems reasonable.
> 
> However, the similar things will sometimes appear as a Nic, then say something new and exciting that indicates that they are actually Nic2 objects (or Nic3, for example).
> 
> The simple/crude solution is just to have one nic object with a '@type' class variable that can get changed once new information appears. Also the @type variable could be queried to figure out what the object is/does.
> 
> But this just doesn't seem like the ruby way. Is there something obvious I should be doing that is sensible and cleaner?

You can deal with this by adding a copy constructor, at least to the
subclasses (but it can be inherited).

class Nic
  def initialize(nic = nil)
    if nic
      self.property = nic.property
      #...
    end
  end
end

class Nic2 < Nic
end

nic = Nic.new
nic = Nic2.new(nic)

Cheers,
Dave