I absolutely agree. There’s prior art in that direction. It’s more or less abandoned now, but Microsoft developed an extension to C++ that integrated the .NET r

I absolutely agree. There’s prior art in that direction. It’s more or less abandoned now, but Microsoft developed an extension to C++ that integrated the .NET runtime with it’s garbage collector called C++/CLI. The way it worked is that in addition to C++’s native pointers and references (Foo* and Foo&), you had a new kind of garbage collected reference, written Foo^. There were some annoying limitations that a GC built directly for this use case might have solved better, but mostly, this worked really well. And I think Rust would be a much better target language for such a system than C++ was. For example, one of the interesting problems was that the .NET GC is compacting — it will move objects around to improve cache locality and simplify the allocation algorithm. To interact with ordinary C++ code, you need native pointers into GC’d objects. But it was only safe to take such a pointer while you told the GC to temporarily “pin” the object in memory, otherwise, your pointer could be randomly invalidated. Forgetting that step was a very evil source of nondeterministic memory bugs. It’s not hard to see how the borrow checker would help there.