What is the reason for the additional indirection in Handle?

[Ramón García]

> Like Keith said, it does both [tracking that pointer is being used and updating the references if the pointer is moved].

Then there is something that I do not understand.

If one is inside a member function of, say, KlassHandle. That
functions receive the value of this as the first (hidden) parameter,
like any C++ method. If the address of KlassHandle changes, how can
this be handled? If it is imposible, why?