mirror of
https://github.com/rust-lang/rust.git
synced 2025-01-30 00:23:41 +00:00
7c1283a068
Remove P: Unpin bound on impl Future for Pin We can safely produce a `Pin<&mut P::Target>` without moving out of the `Pin` by using `Pin::as_mut` directly. The `Unpin` bound was originally added in #56939 following the recommendation of ``@withoutboats`` in https://github.com/rust-lang/rust/issues/55766#issue-378417538 That comment does not give explicit justification for why the bound should be added. The relevant context was: > [ ] Remove `impl<P> Unpin for Pin<P>` > > This impl is not justified by our standard justification for unpin impls: there is no pointer direction between `Pin<P>` and `P`. Its usefulness is covered by the impls for pointers themselves. > > This futures impl (link to the impl changed in this PR) will need to change to add a `P: Unpin` bound. The decision to remove the unconditional impl of `Unpin for Pin` is sound (these days there is just an auto-impl for when `P: Unpin`). But, I think the decision to also add the `Unpin` bound for `impl Future` may have been unnecessary. Or if that's not the case, I'd be very interested to have the argument for why written down somewhere. The bound _appears_ to not be needed, as demonstrated by the change requiring no unsafe code and by the existence of `Pin::as_mut`. |
||
|---|---|---|
| .. | ||
| benches | ||
| src | ||
| tests | ||
| Cargo.toml | ||