Interfacing with XPCOM

John Reimer terminal.node at
Mon Dec 1 17:12:55 PST 2008

Hello Walter,

> John Reimer wrote:
>> It would be nice if extern(C++) were still ported to D 1.0, but the
>> other alternative of enabling extern(System) in COM support (instead
>> of extern(Windows) ) will also work.
> Unfortunately, extern(C++), even if ported to D1, will not work for
> COM objects. COM objects, to be compatible with Windows, need to be
> the Windows calling convention.

Er... Yes, actually my statement above was meant to emphasize the potential 
usefulness of extern(C++) for XPCOM support on Linux among many things.

That said, I'm guessing that even extern(C++) would work fine for COM support 
on windows if one directly declares the interface methods with extern(Windows) 
attribute.  Similar to COM, C++ XPCOM on win32 seems to do this as well: 
it applies stdcall to the XPCOM class (interface) methods.

In D (windows) it would look like so (assuming you have done away with the 
compilers internal detection of COM interfaces):

extern(C++) interface IUnknown:
         int QueryInterface(nsIID* uuid, void **result);
         int AddRef();
         int Release();

I bet it would work fine and would be a good way to avoid the special-cased 
interfaces providing COM support in D.  Instead we've special-cased for C++, 
which is, at least, a more general case. ;-)


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