From: "Ara.T.Howard" <ahoward@...>
Date: 2004-02-13T09:05:00+09:00
Subject: Re: Swapping out an instance between blinks

On Thu, 12 Feb 2004, Gavin Kistner wrote:

> Date: Thu, 12 Feb 2004 23:37:19 GMT
> From: Gavin Kistner <gavin@refinery.com>
> Newsgroups: comp.lang.ruby
> Subject: Swapping out an instance between blinks
> 
> I'm writing a class (which I'm calling MutableTime) that is like a Time 
> object, but...well...mutable :) Changeable in all sorts of magical ways.
> 
> I'd like it to have almost all the methods of Time, so this seems like a 
> clear case for inheritance:
> 
> class MutableTime < Time
> 	#...
> end
> 
> 
> However, I've run into cases where I want to modify some internal values 
> of the instance, and (since Time is written in C) I can't figure out 
> what private instance variables I may or may not have access to.
> 
> For example, I want to let the user change the year:
> 
> 
> class MutableTime < Time
> 	def year=(newYear)
> 		pieces = @t.to_a
> 		pieces[5]=newYear
> 		newTime = Time.local(*pieces)
> 		self = newTime # ERROR
> 	end
> end
> 
> Is there any way to, inside the method for an instance, magically swap 
> out that instance to be represented by a new instance?

class MutableTime
  def initialize time = Time.now
    @time
  end
  def method_missing(meth, *args, &block)
    @time.send(meth, *args, &block)
  end
  def swap other
    @time = other
  end
end

also look at the delegate pattern in the oo library section of the pickaxe.

> (I just realized that I can actually do what I want by making the newTime,
> calculating the difference in seconds from the current time, and then adding
> that in. Which is what I'll do, but I'm still interested in the answer to
> the question above.)

-a
-- 
(short)