1.8 Implementing COM interfaces in Lisp

Lisp implementations of COM interfaces are created by defining an appropriate class and then defining COM methods for all the interfaces implemented by this class.

The class can inherit from standard-i-unknown to obtain an implementation of the i-unknown interface. This superclass provides reference counting and an implementation of the query-interface method that generates COM interface pointers for the interfaces specified in the class definition. It also supports aggregation .

There are two important things to note about COM classes and methods:

• The implementation objects and COM interface pointers are different things: an interface pointer must be queried from the implementation object explicitly and there is no API to obtain an object from an interface pointer, except implicitly within a COM method definition. This is show in The relationship between an Lisp object and its COM interface pointers below.
• COM methods are not defined with defmethod because they have very specific conventions for passing arguments and returning values that are different from those of Lisp.

Figure 1.1 The relationship between an Lisp object and its COM interface pointers

1.8.1 Steps required to implement COM interfaces

1.8.2 The lifecycle of a COM object

1.8.3 Class factories

1.8.4 Unimplemented methods

1.8.5 Inheritance

1.8.6 Data conversion in define-com-method