[pjbk]

You would have thought they learned from their mistakes implementing VST2, but they doubled down going even further basing VST3 on the Windows Component Object Model. I guess it was a decision to avoid reinventing the wheel, but you can quickly realize it is a very bad model for real time audio plugins and audio host support. The API just exploded in complexity, and testing was a nightmare. In contrast you can tell the U-He developers have all the experience from the trenches.

[p0nce]

> it is a very bad model for real time audio plugins and audio host support

COM is just 3 predefined calls in the virtual table. CLAP gives you a bunch of pointers to functions, which is similar.

[jsmith45]

> COM is just 3 predefined calls in the virtual table.

COM can be as simple as that implementation side, at least if your platforms vtable ABI matches COM's perfectly, but it also allows far more complicated implementations where every implemented interface queried will allocate a new distinct object, etc.

I.E. even if you know for sure that the object is implemented in c++, and your platforms' vtable ABI matches COM's perfectly, and you know exactly what interfaces the object you have implements, you cannot legally use dynamic_cast, as there is no requirement that one class inherits from both interfaces. The conceptual "COM object" could instead be implemented as one class per interface, each likely containing a pointer to some shared data class.

This is also why you need to do the ref counting with respect to each distinct interface, since while it is legal from an implementation side to just share one ref count for it all, that is in no way required.

[debugnik]

Note that VST3 doesn't implement the COM vtable layout, their COM-like FUnknown really is just 3 virtual methods and a bunch of GUIDs. They rely on the platform's C++ ABI not breaking.

You're right that QueryInterface can return a different object, but that doesn't make it significantly more complicated, assuming you're not managing the ref-counts manually.

[p0nce]

Yes, ironically the COM in AAX and COM in VST3 have slightly different layouts.