A lot of it is/was driven by the historical instability of the C++ ABI, itself driven by instability in the language. If you made an object with a C based patte

A lot of it is/was driven by the historical instability of the C++ ABI, itself driven by instability in the language. If you made an object with a C based pattern, you could export a binary compatible interface and use dynamic linking. If you exported the same object as C++, even if it boiled down to the same thing, your users might get crashes because two compilers disagreed on the right way to compile it. That's the origin of COM. It's basically the C mything_mystruct pattern with a lot of additional stuff on top. Actual COM objects were usually implemented in C++ though.