Tracking Issue for raw-pointer-to-reference conversion methods · Issue #122034 · rust-lang/rust (original) (raw)
Feature gate: #![feature(as_ref_unchecked)] (or similar)
This is a tracking issue for raw-pointer-to-reference conversion methods (rust-lang/libs-team#342).
With #106116, we have methods for almost all casts/conversions one wants to do on references and pointers, to avoid as casts and prefix operators. Just one direction is missing: turning raw pointers into references. Here we have as_ref/as_mut, but they behave different from &*ptr/&mut *ptr: they return an Option and perform a null-check. (These are the only methods on raw pointers that perform a null check.)
Public API
impl *const T { unsafe const fn as_ref_unchecked<'a>(self) -> &'a T { &*self } } impl *mut T { unsafe const fn as_ref_unchecked<'a>(self) -> &'a T { &*self } unsafe const fn as_mut_unchecked<'a>(self) -> &'a mut T { &mut *self } }
Motivating examples or use cases
Some random examples from a quick grep of the rustc sources:
&mut *(out as *mut &mut dyn PrintBackendInfo) &mut *(state as *mut &mut dyn FnMut(&[u8]) -> io::Result<()>) &mut *(self.0 as *mut _) &mut *(vec as *mut Vec) &mut *(value as *mut T as *mut UnsafeCell) &mut *(s as *mut T).cast::<[T; 1]>()
The examples above then become
out.cast::<&mut dyn PrintBackendInfo>().as_mut_unchecked() state.cast::<&mut dyn FnMut(&[u8]) -> io::Result<()>>().as_mut_unchecked() self.0.cast().as_mut_unchecked() vec.cast::<Vec>().as_mut_unchecked() ptr::from_mut(value).cast::<UnsafeCell>().as_mut_unchecked() ptr::from_mut(s).cast::<[T; 1]>().as_mut_unchecked()
Unfortunately, since the as_mut name is already taken, these are all longer than the prefix variants. But they can be read left-to-right which is an advantage.
Steps / History
- Implementation: Implement ptr_as_ref_unchecked #122492
- Final comment period (FCP)1
- Stabilization PR
Unresolved Questions
- Is there a shorter name we could use?