2.2 Overview of OLE/COM and the Functional Developer API
2.2.3 Representing interfaces
COM represents interfaces using a simple table-and-pointer mechanism. When a client connects to an object and requests an interface, it receives a C pointer to the interface. The interface pointer leads to a table of pointers (called a vtable) each of which point to the COM methods of the interface.
Suppose there was an interface IPaint with the methods Draw and Fill in addition to the methods QueryInterface, AddRef and Release that are inherited from IUnknown. Figure 2.4 shows how a connection to IPaint would be represented.
Figure 2.4 COM interface representation.
In an OLE/COM application built with Functional Developer libraries, you often do not need to represent COM interfaces, classes, or methods explicitly. The libraries instead provide high-level protocols that implement the necessary COM details for you. You may be required to implement certain Dylan methods or extend certain Dylan classes, but usually do not need to represent a COM class, interface, or method directly. This is very convenient, and adequate for most applications.