`flatModify` should be uncancelable

[armanbilge]

This has binary-compat implications but fortunately has not been released yet. Opened an issue so we don't forget. h/t @bpholt

cats-effect/kernel/shared/src/main/scala/cats/effect/kernel/Ref.scala

Line 106 in 52b5a3b

def flatModify[B](f: A => (A, F[B]))(implicit F: FlatMap[F]): F[B] = F.flatten(modify(f))

[djspiewak]

Shouldn't this be user choice? It has semantic implications that vary a bit depending on the use case.

[armanbilge]

Hmm, I was thinking about the border between completing the modify and beginning the effect. Of course, the effect itself might be cancelable. Something like this:

def flatModify[B](f: A => (A, F[B]))(implicit F: MonadCancel[F]): F[B] =
  F.uncancelable { poll =>
    modify(f).flatMap(fb => poll(fb))
  }

[armanbilge]

Eh, I'll just make a new issue.