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by cesarb 1453 days ago
> Using a pure C interface escapes COM's requirement to register every component (regsvr32) [...] Another alternative if you want to stick with C++: make up your own lightweight COM

Or you can combine both: use a pure C interface which returns COM objects. That way, you can keep using COM without having to register anything with regsvr32 or similar.

> I have no idea if this trick will also work on Linux, I don't know how stable GCC / Clang's vtable layout is from version to version

Recent (as in, since around the turn of the millennium) GCC and clang on Linux use a standard vtable layout, defined by the "Itanium ABI" (originally created for Intel's IA-64, but like UEFI and GPT, became a standard across all architectures), so it's also very stable.
2 comments
p_l 1452 days ago
Itanium ABI is somewhat stable. As in there exists a chance that two binary files compiled with exact same set of libraries and headers will be compatible, which is something that will get broken the moment two files were compiled with different switches in GCC that do not technically change things at Itanium ABI levels, but cause incompatibilities in various standard types.
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olvy0 1453 days ago
Ah! Yeah, I've completely forgotten that the Itanium ABI also guarantees a standard vtable layout. Thanks!

Were starting to convert my app from a Windows-only app to a cross platform one, so this makes me happy that my "COM lite" scheme would also be stable on linux.

As for returning pure COM objects through a C interface: Yeah, I've considered that, but like I wrote in my comment below to pjmlp, I don't like COM personally, and I want to simplify writing the components' code as much as possible, since the team which writes them isn't a team of software developers but rather in a supporting role. They do know basic C++/C# but don't know COM.

Also getting rid of COM would be the first thing done for cross platform support, anyway.

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p_l 1452 days ago
Due to experience trying to link some code, especially C++, I'd probably rather start by implementing a simplified COM system first rather than dealing with extern C
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