COM接口中VARIANT的专有使用

Question

I've inherited a project that includes a COM DLL. I'm sort of new to COM but something doesn't seem right. The interface defined in the IDL only uses the VARIANT type for all properties and method returns/parameters. Is there any possible justification for this? I have a feeling the previous developer was just winging some things, but I want to be sure.

Here's what my IDL looks like:

interface IMyComInterface : IDispatch
{
    [id(1), helpstring("method CheckMessage")] HRESULT CheckMessage([in] VARIANT vMsg);
    [id(2), helpstring("method CheckFolder")] HRESULT CheckFolder([in] VARIANT Folder, [out] VARIANT *pCount, [out, retval] VARIANT *pErrorCount);
    [propget, id(3), helpstring("property Flags")] HRESULT Flags([out, retval] VARIANT *pVal);
    [propput, id(3), helpstring("property Flags")] HRESULT Flags([in] VARIANT newVal);
    [propget, id(4), helpstring("property MessageStore")] HRESULT MessageStore([out, retval] VARIANT *pVal);
    [propput, id(4), helpstring("property MessageStore")] HRESULT MessageStore([in] VARIANT newVal);
    [propget, id(5), helpstring("property Directory")] HRESULT Directory([out, retval] VARIANT *pVal);
    [propput, id(5), helpstring("property Directory")] HRESULT Directory([in] VARIANT newVal);
    [propget, id(6), helpstring("property MessageCount")] HRESULT MessageCount([out, retval] VARIANT *pVal);
};

Much thanks.

EDIT:

To make things clear, all of these VARIANT s could be replaced by explicit types.

Answer 1

If you need performance or simplification, you change VARIANT type for appropriate values, more closely to type used. Remember, it is an interface break.
View valid values to use :
COM Data Types

Answer 2

Your interface derives from IDispatch which means it's a dual interface - you can call the methods directly from the interface, or you can call them through iDispatch::Invoke . The parameters passed to Invoke must all be of type VARIANTARG which is just another name for VARIANT , see http://msdn.microsoft.com/en-us/library/ms891678.aspx .

Answer 3

For certain types of dual interfaces that suppose to work with VB and scripting languages it is better to use VARIANT that direct type. For example it is better to use VARIANT over almost all kind of SAFEARRAY and interface pointers. But you may test and see.