From: Gavin Kistner <gavin@...>
Date: 2004-02-13T08:39:57+09:00
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?


(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.)