Struct PinHelper 

#[repr(transparent)]
pub struct PinHelper<Ptr> {
    pointer: Ptr,
}

🔬This is a nightly-only experimental API. (pin_derefmut_internals)

Helper that prevents downstream crates from implementing DerefMut for Pin.

The Pin type implements the unsafe trait PinCoerceUnsized, which essentially requires that the type does not have a malicious Deref or DerefMut impl. However, without this helper module, downstream crates are able to write impl DerefMut for Pin<LocalType> as long as it does not overlap with the impl provided by stdlib. This is because Pin is #[fundamental], so stdlib promises to never implement traits for Pin that it does not implement today.

However, this is problematic. Downstream crates could implement DerefMut for Pin<&LocalType>, and they could do so maliciously. To prevent this, the implementation for Pin delegates to this helper module. Since helper::Pin is not #[fundamental], the orphan rules assume that stdlib might implement helper::DerefMut for helper::Pin<&_> in the future. Because of this, downstream crates can no longer provide an implementation of DerefMut for Pin<&_>, as it might overlap with a trait impl that, according to the orphan rules, the stdlib could introduce without a breaking change in a future release.

See https://github.com/rust-lang/rust/issues/85099 for the issue this fixes.

Fields

pointer: Ptr

🔬This is a nightly-only experimental API. (pin_derefmut_internals)

Trait Implementations

impl<Ptr: DerefMut> PinDerefMutHelper for PinHelper<Ptr>

where Ptr::Target: Unpin,

type Target = <Ptr as Deref>::Target

🔬This is a nightly-only experimental API. (pin_derefmut_internals)

fn deref_mut(&mut self) -> &mut Ptr::Target

🔬This is a nightly-only experimental API. (pin_derefmut_internals)