Essential .NET, Volume 1: The Common Language Runtime

Interfaces, Virtual Methods, and Abstract Methods

The CLR deals with objects and interface types differently than its predecessors (C++ and COM). In C++ and COM, a given concrete type has one method table per base type or supported interface. In contrast, a given concrete type in the CLR has exactly one method table. By inference, a CLR-based object has exactly one type handle. This is in stark contrast to C++ and COM, where an object would routinely have one vptr per base type or interface. For this reason, the CLR's castclass does not result in a second pointer value in the same way as C++'s dynamic_cast or COM's QueryInterface.

Each CLR type has a single method table independent of its type hierarchy. The initial slots in the method table ...