From: Jason Voegele <jason@...>
Date: 2003-02-10T08:02:13+09:00
Subject: Trapping Access/Modification of Objects

After a long delay, I'm now starting to work on the RubyGOODS library 
again.  This library is intended to provide an interface to the GOODS OO 
database, as well as serve as a more generic object persistence library 
(eventually including an object-relational mapping layer).

What I'm actually working on now is an API based on the ODMG's Object 
Data Standard 3.0.  To support this API, I need to be able to track, in 
a generic fashion, when objects are accessed and modified.  This job 
would be simpler if I could simply wait until the end of a transaction 
and compare live objects to snapshots of those objects as they existed 
at the beginning of the transaction.  Unfortunately, I need to obtain a 
lock on an object PRIOR TO the access or modification.

I'm using proxy objects and AspectR to handle some of this 
functionality, so I am able to trap all accesses to any persistent 
object.  However, I haven't been able to think of any way to determine 
if the object is about to be modified.  The closest I can come is to 
rely on the conventions of modifier methods ending in '=' or '!'.  But 
this is not 100% reliable, considering methods such as Array#delete. 
The only other way I can think of is to have users of the library call 
some method to explicitly indicate that an object is about to be 
modified, but I'd prefer a more transparent solution.

Does anyone have any thoughts?

Thanks.
-- 
Jason Voegele
"There is an essential core at the center of each man and woman that
remains unaltered no matter how life's externals may be transformed
or recombined. But it's smaller than we think."
     -- Gene Wolfe, The Book of the Long Sun