Using a COM interface generated by CsWin32 implemented on a custom .NET object.

[Tape-Worm]

Hi, I have an object that implements the IStream.Interface generated by CsWin32. I use this to wrap a .NET Stream type so I can pass it to COM interfaces.

The problem is, I don't know of a good way to extract the IStream* interface from the wrapper object without using Marshal.GetComInterfaceForObject. This, of course, this makes AOT fail.

I've read about ComWrappers, but they look brutal to implement, and it seems like CsWin32 already does something pretty close to ComWrappers on my behalf. I'm sure I'm just missing something or doing something really dumb.

Is there a better, more AOT friendly way to make this work?

Thank you!

In case it's necessary, this is the use case:

unsafe void Method(Stream theStream)
{
  IThingThatConsumesIStream *thatThing = // Assume that I instanced this and it's working.
  
  // Now, we need to pass the stream to the consumer.
  using StreamComWrapper wrapper = new(theStream);
  IStream* comStream = wrapper.ToIStream(); // <-- This is where GetComInterfaceForObject comes in.
  
  thatThing->DoTheThing(comStream); // <-- Requires an IStream*, not my interface, so I can't change it.
  
  thatThing->Release();
}

[Tape-Worm]

Well, I worked around this by writing my own com wrapper using the ComWrappers type (not as brutal as that "tutorial" on Microsoft's site made it seem) and providing my own implementation to CsWin32's IStream.Interface. Seems to be working thus far, and AOT seems to be happy with it.

[Tape-Worm]

For the love of all that is good and holy, do not put in void where HRESULT is expected. Strange and magical terrors lie that way.

Ask me how I know.