Chapter 14: Type Libraries

In addition to implementing dual interfaces, you should create a type library for each set of objects you expose. Because VTBL references are bound at compile time, exposed objects that support VTBL binding must be described in a type library.

Type libraries provide these important benefits:

Type checking can be performed at compile time, helping developers of OLE Automation controllers to write fast, correct code to access your objects.
You can use the DispInvoke function to implement IDispatch automatically. Using DispInvoke ensures that your implementation will be correct.
Visual Basic applications can create objects with specific interface types, rather than the generic Object type, and take advantage of early binding.
OLE Automation controllers that don't support VTBLs can read and cache DISPIDs at compile time, thereby improving run time performance.
Type browsers can scan the library, allowing others to see the characteristics of your objects.
The RegisterTypeLib function can be used to register your exposed objects.
Local server access is improved, because OLE Automation uses information from the type library to package the parameters passed to an object in another process.