I've just been reading through some academic papers by Tom Mens. The paper at this link looks interesting, as it appears to me to describe a problem that is addressed in Zope by acquisition wrappers. http://prog.vub.ac.be/Research/ResearchPublicationsDetail2.asp?paperID=51 Abstract Most object-oriented languages provide a self pseudo variable that serves two purposes: invoking methods through self sends and returning a self reference. Current formal models capture this behaviour by introducing a self parameter that fulfils both roles. We will show that this double functionality is incompatible with object-based encapsulation. Moreover we will point out that the separation of both functionalities is needed in type systems. We propose a formal model based on a primitive self send construct, and present its denotational semantics. A self reference is implemented through a self send instead of the other way around. This model is extended formally with an object-based encapsulation mechanism. It allows us to keep inheritance, encapsulation and typing orthogonal. This way we obtain a flexible and incremental software development scheme. In the case of Zope, the "self sends" are represented by the way an acquisition wrapper dispatches messages. The "self reference" is given by aq_base (or one of the other aq_ attributes, depending on what you want "self" to mean at the time). -- Steve Alexander Software Engineer Cat-Box limited http://www.cat-box.net