[Mitranim]

Interesting! Nice that the approach is known, and others are being discussed. I should check GTOR again.

Multicast cancelation based on refcounting doesn't look right to me. I explicitly avoided this in Posterus, sticking with exclusive ownership, what GTOR calls unicast (thanks for linking). The reason is that subscribers may come and go over time. I've seen, and written, code that caches a promise and reuses it many times. It may start with one consumer, lose it, be canceled, then another consumer comes and gets rejected. This just feels like a big footgun. In Posterus, multicast is explicit and opt-in (`.weak()` futures).

If we eventually standardise a solution, I'd like something with as few interfaces as possible. In a dynamic language, you don't have the luxury of creating a future that initialises into a task, returning a cancelation token. Too many types without static checking is just a footgun. This is part of why Posterus only has futures, why cancelation is provided in the future constructor and tied to the future itself, and why they're eager rather than lazy. Deviating from these constraints would introduce new types, increasing the footgun potential.