Make implementing cancellation possible

[ForbesLindesay]

No description provided.

[buffpojken]

Any thoughts on this?

As in, I find myself in need of this and might do a stab at implementing it, but what are you looking for in terms of implementation?

EDIT: Clarification

[ForbesLindesay]

The goal here is to track what happens in https://github.com/promises-aplus/cancellation-spec and consider building a prototype of one of the suggestions in there. Unfortunately cancellation (along with progress) have yet to make it into any formal specification for how promises work.

Personally I'm in favor of Cancellation Tokens (promises-aplus/cancellation-spec#8). These work really well in the .net world, and have the added bonus of not requiring any modification to then/promise.

https://github.com/ForbesLindesay/cancellation contains a prototype implementation of the idea, which I would be happy to expand upon/collaborate on.

[edef1c]

My preferred approach (and the semantically most sensible approach) to cancellation does not actually require being part of the Promise implementation, so I consider this issue obsolete.