This article is from the Object-Oriented Technology FAQ, by Bob Hathaway firstname.lastname@example.org with numerous contributions by others.
Downcasting is the term used in C++ for casting a pointer or reference to
a base class to a derived class. This should usually be checked with an
embedded dynamic typing scheme if such a scheme is not present in the
language, such as with a typecase (Modula-3) or inspect (Simula) construct.
In C++, it is even possible to use conversion functions to perform some
checks, although the proposed RTTI will perform checked downcasting as
its primary ability.