They have created a new precise reference-counting algorithm, called Perceus: https://www.microsoft.com/en-us/research/uploads/prod/2020/1...

Its innovation (they claim) is that it deallocates objects immediately as soon as it can prove that the object is not referenced any more. Not at the end of a lexical scope, like C++ smart pointers and Rust, but immediately after the last use of the object.

Interestingly, in Rust, we thought about doing this. "early drop" was the term folks talked about https://github.com/rust-lang/rfcs/pull/239

One big concern was that there's a lot of pre-existing unsafe code that could rely on the drop being at the end of the scope, and not earlier. And you could imagine where, in a world with early drop, maybe you write some unsafe that's sound, but then the safe code changes, something gets dropped earlier, and now it's not sound anymore.

This doesn't mean that this affects Koka, I haven't spent any time with it yet and so I don't mean to imply this is the wrong decision, just showing some related work.