COM inheritance Q

Robert Shearman rob at
Thu Jan 13 15:21:27 CST 2005

Mike Hearn wrote:

>On Thu, 13 Jan 2005 20:33:10 +0000, Ann and Jason Edmeades wrote:
>>Whats the solution?
>>In d3d8 I would have coded IWineD3DSurfaceImpl_GetParent as
>>IWineD3DResourceImpl_GetParent(iface, pParent) because the Impl versions
>>were prototyped - Is this the only way to solve this?
>I'm kind of confused too but it seems you really want two interfaces
>that inherit from each other here rather than having two separate
>interfaces that happen to have the same name.
>So, IWineD3DSurface should inherit from IWineD3DResource which in
>turn should inherit from IUnknown. Then you fill out the vtable
>appropriately for overrides. Isn't object orientation in C fun :)
>typedef struct
>     IWineD3DSurfaceVtbl *lpVtbl;
>     DWORD refcount;
>     ....
>} WineD3DSurface;
>static IWineD3DSurfaceVtbl SurfaceVtbl = {
>     /* IUnknown methods are reimplemented per object here but you could be cleverer */
>     WineD3DSurface_QueryInterface,
>     WineD3DSurface_AddRef,
>     WineD3DSurface_Release,
>     /* Now for the Resource methods */
>     WineD3DResource_XXX,
>     WineD3DResource_YYY,
>     /* Now for the Surface methods */
>     WineD3DSurface_AAA,
>     WineD3DSurface_BBB

But you'll get a warning because the WineD3DResource functions will take 
a different type iface variable as their first parameter. You could cast 
it to the correct type, but you'll lose all type checking on the 
function and I wouldn't recommend it.


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