How to intercept every instance variable write on all objects

Hello, is possible to intercept (before writeú all instance variable writes on every existing objects? I found a discussion here: http://forum.world.st/Is-it-possible-to-follow-an-object-through-a-computati... Known solutions: 1) jugglery with object read only state + ModificationForbidden - not ideal, it's probably slow via exceptions and every nested on:do: stop change detection 2) it's possible to do it via slots - but it does not work on any existing object (only on my specially prepared objects with slots) 3) Metalinks - it's based on intercepting method calls, right? But I need to intercept direct instance variable write, so probably not possible Is there any way? Thanks! pf