[ptx]

One of the niches where it's found a lot of popularity is Android development, which naturally leads developers to thinking about sharing code with the iOS version of their app. This is where Kotlin Native fits in, I think.

Also (just dreaming here) if Kotlin Native were to use some kind of Swift-like reference counting rather than a traditional GC, it could be really nice for interfacing with COM on Windows, where you need to be able to release references to COM objects immediately and possibly in a specific order. In a language with GC, your objects might not be collected soon enough, which leaves the references alive and the process hosting the COM object unable to shut down.

[mwcampbell]

I agree with you about the potential of Kotlin Native. And I, too, would like reference counting, at least as an alternative to GC.

But I think that for really smooth interop with the host platform, it won't be good enough to have just one generic Kotlin Native, that compiles to native code with a cross-platform compiler infrastructure like LLVM. It would be much better to have multiple Kotlin native implementations that integrate well with various host platforms. For example:

* Kotlin for Apple platforms: Every Kotlin object is an ObjC object, and ObjC APIs can be used with minimal glue code in optimized builds. All Kotlin strings are NSStrings and vice versa. Same with collections (NSArray, NSDictionary, and their mutable counterparts); Kotlin's separation of read-only and mutable interfaces is a good match for this platform.

* Kotlin for Universal Windows Platform: UWP, being COM-based, doesn't have a root object type like the Apple platforms. Still, we'll want to be able to call UWP APIs and implement UWP interfaces with minimal runtime glue. And UWP has a reference-counted immutable string type (HSTRING), so all HSTRINGs should be Kotlin strings and vice versa. I don't recall how collections work on UWP.

* Kotlin for classic Win32 + COM: Similar to UWP, but the situation with strings is more complicated. BSTR isn't reference counted, so on this platform, Kotlin would probably need to have its own string implementation, with bridging to and from BSTR for COM interfaces.

[pjmlp]

.NET and .NET Native work perfectly fine with COM, in spite of having a GC.

[ptx]

Only if you make sure to call Marshal.ReleaseComObject on all your objects, which requires you to hang on to explicit references to all of them, which is not very convenient for many COM APIs, e.g.

   Application.Database.Classes.Item("MyClass").Refresh()

where you would have to save all the intermediate objects in variables just so you can destroy them.

Python works much better with COM, in my experience, because of its more primitive but more predictable reference counting.

[pjmlp]

I use .NET since pre-alpha days and never used it, RCW and CCW take care of that.

Unless you are talking about manually loading them.

Also, are you aware that UWP and .NET Native are built on COM?

[ptx]

I have run into this problem in two cases:

1. When writing a COM add-in for a host application. When the application wants to shut down, the add-in must release all references to the objects of the host application, otherwise the process doesn't shut down. (At least with the application I'm currently writing an add-in for!)

2. When using out-of-process COM servers such as Excel from another application. This tends to leave lots of "excel.exe" processes running unless you explicitly release everything.

See for example: https://www.add-in-express.com/creating-addins-blog/2013/11/...

Here is Microsoft describing how they ran into this problem when mixing COM and .NET in Visual Studio, how they solved it using Marshal.ReleaseComObject, how that itself caused other problems later when they combined it with CCW, and ... I'm not sure what their ultimate correct solution was:

https://blogs.msdn.microsoft.com/vcblog/2006/09/19/mixing-de...

https://blogs.msdn.microsoft.com/visualstudio/2010/03/01/mar...

I am aware of UWP bringing COM back into fashion again, which is why I'm interested in potentially using Kotlin Native with it. :)

[mwcampbell]

I've run into this kind of problem while implementing a Windows screen reader that needs to use COM-based accessibility APIs, both in-process and out-of-process. I naively chose, some 12 years ago, to use Lua, even for the in-process component. Lua, of course, uses tracing garbage collection, not reference counting.

[pjmlp]

Thanks for the explanation and links.

I guess the reason for never bumping into it was that all use cases I encountered so far, the controls were in-process and died when the application terminated.