Error-code and exception-based function dispatch tables

A condition detected by a virtual routine may be treated by setting an error code or raising an exception, depending on circumstances. Enhanced vtable layouts promote availability of both error-ID-based and exception-based virtual routines, while maintaining compatibility. Compilers treat virtual routines based on their circumstances. One enhanced vtable includes error-ID-based routine pointers in a COM-layout-compatible portion and exception-based routine pointers in an extension. For a virtual routine not overridden by a derived class, a compiler generates a direct call. For an object instance of a specific type, the compiler generates a direct exception-based call for the object's routine. For a factory-sourced object's routine, the compiler generates a virtual exception-based call. When the virtual routine belongs to a component having an enhanced vtable, the compiler may generate a virtual call using the exception-based routine pointer. Code wrappers between COM and native format may also be used.