Interfacing with XPCOM

[Walter Bright]

John Reimer wrote:
> Hello Walter,
> 
>> So are you saying that XPCOM will work on Linux with D if only the
>> extern(Windows) was actually extern(C++) ?
>>
> 
> 
> Yes, I think so.  But I should probably test the theory with dmd 2.0 
> first just to make sure.  This is just about over my head since I'm not 
> too familiar with C++ internals.  In terms of XPCOM, I believe that when 
> an interface is assigned an implementation pointer and the interface 
> method is called, the most important detail is that the /parameter/ 
> signature at a specific vtable index match that of the implementation's 
> at the same index:  that is, the method names are not important except 
> as an alias for client to use; it is assumed that the interface methods 
> will match the calling convention and argument types of the 
> implementation which was assigned to it).
> 
> So my question would be, in terms /calling conventions/ in an 
> /interface/ (not a class), does extern(System)  differ in any way from 
> extern(C++).  Does a "this" pointer get prepended to the argument list 
> of a C++ method call?  I apologize if this is an ignorant question.  I'm 
> almost clueless here.  I'm assuming that the only difference in the 
> extern(C++) is that it:
> 
> (1) changes the interface to have a "normal" vtable (as XPCOM needs) and
> (2) allows for a system calling convention (method name not being 
> important other than that the parameters of interface and implementation 
> match).

The system linkage was devised to match the Microsoft "syscall" 
convention. It really has no meaning on linux, so we can make it 
whatever it needs to be.

The C++ convention is designed to match whatever C++ does on the target 
platform. Since Linux doesn't have any Windows or System calling 
convention, it would seem that C++ is the one.