[Tamschi]

There's a hole or oversight in `Arc`'s API in this regard, annoyingly. The function you're looking for would be something like

pub fn get_mut_pinned(this: &mut Pin<Arc<T>>) -> Option<Pin<&mut T>>

, which for pinning-aware values should give you enough mutability and for `T: Unpin` can give you `Option<&mut T>` through `Option::as_deref_mut`. Unfortunately, I haven't seen any `Arc` implementations that actually provide it, since almost none of the third-party ones are pinning-aware. (My `tiptoe::Arc`'s `get_mut` has this signature, but that's a specialty container with additional requirements for the contained value.)

The same goes for `make_mut_pinned`, that's missing too (but to be fair would be much less useful, since pinning and `Clone` don't often mix that well).

[zozbot234]

Have you tried proposing these API's on the internals.rust-lang.org forum or via posting a proposed RFC? It's not clear to me if they're sound in the general case, but if that's the case they can absolutely be added.

[Tamschi]

I should. I'm not too familiar with the process so far, but I'll find some time for it.

These functions are indeed generally sound (also for `Rc`), as any value that cares would be `!Unpin`, which would still bar access to `&mut T`. `make_mut_pinned` also shouldn't cause too much confusion, as availability of `Clone` would have to be declared explicitly just about everywhere that's relevant.

They can be implemented as very thin wrappers around their non-pinning equivalents, with only a few `unsafe` operations to make the types fit.

[zozbot234]

> I should. I'm not too familiar with the process so far, but I'll find some time for it.

The internals forum is good for informal discussion, so start there. Posting a RFC proposal is of course the formal step for actually getting the feature included in Rust proper.