alt Hacker NewsCool, yes. Useful or a good idea, I dunno. Reading through the (non-reference) documentation on SOM, I’m struck by how they never could give a convincing example for the utility of metaclasses. (Saying this as someone who does love metaclasses in Python, which are of course an inferior interpretation of the same academic sources.) The SOM documentation is also surprisingly shallow given its size: with a copy of Brockschmidt, Box, the COM spec, and the Platform SDK manual, you could reimplement essentially all of COM (not ActiveX though), whereas the IBM’s documentation is more like “here’s how you use our IDL compiler and here are the functions you can call”. (This is in contrast with the Presentation Manager documentation, which is much tighter and more detailed than the one for USER/GDI ever has been.) From what I can infer of the underlying principles, I feel SOM is much more specific about its object model, which, given the goal is a cross-language ABI, is not necessarily a good thing. (I’d say that about WinRT too.)
And of course COM does do implementation inheritance: despite all the admonitions to the contrary, that’s what aggregation is! If you want a more conventional model and even some surprisingly fancy stuff like the base methods governing the derived ones and not vice versa, BETA-style, then WinRT inheritance[1] is a very thin layer on top of aggregation that accomplishes that. Now if only anybody at Microsoft bothered to document it. As in, at all.
(I don’t mean to say COM is my ideal object model/ABI. That would probably a bit closer to Objective-C: see the Maru[2]/Cola/Idst[3] object model and cobj[4,5] for the general direction.)
[1] https://www.interact-sw.co.uk/iangblog/2011/09/25/native-win...
[2] https://web.archive.org/web/20250507145031/https://piumarta....
[3] https://web.archive.org/web/20250525213528/https://www.piuma...
[4] https://dotat.at/@/2007-04-16-awash-in-a-c-of-objects.html
Replies
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.
Because at the time it was obvious, Smalltalk was the C++ companion on OS/2, a bit like VB and .NET came to be on Windows years later.
Aggregation is not inheritance, rather a workaround, using delegation. And it has been always a bit of the pain to set up, if one wants to avoid writing all the boilerplate by hand.
As for WinRT, I used to have it in high regard, until Microsoft management managed to kill everything good that UWP was all about, and now only folks that cannot avoid it, or Microsoft employees on Windows team, care about its existence.