Win32 headers: Problem with COM interface indirection levels

[Don Clugston]

Michael Butscher wrote:
> Hi,
> 
> there seems to be a rather fundamental error in the translation of COM 
> interfaces by the Win32 bindings project:
> 
> The C++ headers defines an interface as a class (more precisely a 
> struct) with some virtual methods. This means, an instance of the 
> interface is the actual object data, mainly containing a pointer to the 
> vtable.
> 
> In D, an interface is a pointer to the object data which contains in 
> turn the pointer to the vtable.
> 
> Because of the different level of indirection e.g. the IShellFolder 
> interface in D is in fact equivalent to the LPSHELLFOLDER type in C++.
> 
> 
> I think there are two possible solutions:
> 
> 1. Modify parameter types of all functions using the interface, e.g. 
> translate C++ definition:
> 
>   HRESULT SHGetDesktopFolder(LPSHELLFOLDER*);
> 
> 
> to:
>   
>   HRESULT SHGetDesktopFolder(LPSHELLFOLDER);
> 
> or:
> 
>   HRESULT SHGetDesktopFolder(IShellFolder*);
> 
> 
> 
> 
> 2. Rewrite the definitions of the LP... types as aliases of the 
> interfaces (I would prefer that), e.g.
> 
> C++:
> 
>   typedef IShellFolder *LPSHELLFOLDER;
> 
> 
> to D:
> 
>   alias IShellFolder LPSHELLFOLDER;

I think you're right (and I'm probably responsible for most of it). It's a 
straightforward but fundamental error. Essentially, there's already a * in the 
definition of a D class. The second way is how it should be.
Should be straightforward to fix with a simple bit of grepping.