I think you misunderstood the quote. Specifically, "even if presented figuratively", and "Many programs are loaded with “assignment-style” operations now done b

I think you misunderstood the quote. Specifically, "even if presented figuratively", and "Many programs are loaded with “assignment-style” operations now done by more expensive attached procedures". Setters are assignment-style operations, and a.f() is an attached procedure. Also, in http://www.c2.com/cgi/wiki?AlanKayOnMessaging http://www.c2.com/cgi/wiki?AlanKayOnMessaging you can see "[I realized] that assignments are a metalevel change from functions, and therefore should not be dealt with at the same level - this was one of the motivations to encapsulate these kinds of state changes, and not let them be done willy nilly" Alan Kay really is for segregating mutable state.