That's because the core of COM is just a function table with fixed 3 initial entries (QueryInterface/AddRef/Release). I had a toy language that implemented COM and compiled to native code, it produced binaries that could run _both_ on Novel Netware and Windows (Netware added support for PE binaries in 98, I think).

The dark corner of COM was IDispatch.

Yeah, IUnknown is so simple there isn’t really much to implement (that’s not a complaint). I meant to reimplement enough of the runtime that it, say, can meaningfully use IMarshal, load proxy/stub DLLs, and such.

As for IDispatch, it’s indeed underdocumented—there’s some stuff in the patents that goes beyond the official docs but it’s not much—and also has pieces that were simply never used for anything, like the IID and LCID arguments to GetIDsOfNames. Thankfully, it also sucks: both from the general COM perspective (don’t take it from me, take it from Box et al. in Effective COM) and that of the problem it solves (literally the first contact with a language that wasn’t VB resulted in IDispatchEx, changing the paradigm quite substantially). So there isn’t much of an urge to do something like it for fun. Joel Spolsky’s palpable arrogance about the design[1,2] reads quite differently with that in mind.

[1] https://www.joelonsoftware.com/2000/03/19/two-stories/ (as best as I can tell, the App Architecture villains were attempting to sell him on Emacs- or Eclipse-style extensibility, and he failed to understand that)

[2] https://www.joelonsoftware.com/2006/06/16/my-first-billg-rev...