For dual and dispatch interfaces, the data types that can be used with COM are restricted to a list of
autemation-compatible data types.

The Invoke method of the IDispatch interface accepts an array
of VARIANTdata types. The :VARIANTis a union of many different data types, such as BYTE,SHORT,LONG,
FLOAT,DOUBLE,BSTR, IUnknown*, IDispatch*, and so on.

VARIANTShave been easy to use from Visual
Basic, but it was complex to use them from C++ .. NET has the Object class instead of VARIANTS.
With custom interfaces, all data types available with C++ can be used with COM. However, this also
restricts the clients that can use this component to certain programming languages.