COM Interface Support Between 32-bit and 64-bit Processes

It is possible for COM interfaces to be called out-of-process from a 32-bit client to a 64-bit server, or vice versa. Window handles are valid across this boundary, but you should take care with pointers that are exposed in the interface.

For example, the out parameter of the following AutoCAD COM interface method has been redefined to return a pointer to a LONG_PTR value rather than a pointer to long:

interface IAcadObject : IDispatch
{
    HRESULT ObjectID([out, retval] LONG_PTR *ObjectId32);
    [
        propget,
        id(0x00000406),
        nonbrowsable,
        helpcontext(IDH_APPLICATION),
        helpstringcontext(AXOBJECTS_IDL_210)
    ]