> in most languages I'm pretty sure the language being referenced was Common Lisp, which supports multiple dispatch (in CLOS). In a multiple-dispatch OOP syste

> in most languages I'm pretty sure the language being referenced was Common Lisp, which supports multiple dispatch (in CLOS). In a multiple-dispatch OOP system methods can be specialized based on any argument—this is somewhat like ADL in C++ but more generalized. Ergo, a new implementation of 'user' can override or extend more generic versions of 'is_blocked'.