From: Jim Cain <list@...>
Date: 2003-07-03T15:16:58+09:00
Subject: Auto-serialization (as in Vapor, sql-serialize, etc.): detecting changes to instance variables

All,

I'm working on the same problem as has been encountered in the projects 
named above: It would be very handy to have a way to trap changes to an 
instance variable... perhaps a callback in the same spirit as 
Kernel#trace_var. To be really useful it would have to be attached to 
the instance variable itself, not just to the accessor methods.

There is a problem even with this low level of control, however. Suppose 
you have a reference R outside of a particular object S that you're 
interested in serializing, and that the reference R points to an object 
that one of S's instance variables points to. In other words, this is true:

R.equal?(S.iv)

How can you detect, from S, that a change to S.iv has been made through 
R, without doing something like comparing the before and after 
serializations of S? Would it be possible to create a callback that was 
attached to the referred-to object (*R or *S.iv in C-speak), rather than 
to the instance variable?

Food for thought.

Cheers,
Jim