Tracking Issue for `slice_as_array`

[bjoernager]

Feature gate: #![feature(slice_as_array)]

This is a tracking issue for adding conversion functions from slices to arrays.

Public API

impl<T> [T] {
    pub const fn as_array<const N: usize>(&self) -> Option<&[T; N]>;

    pub const fn as_mut_array<const N: usize>(&mut self) -> Option<&mut [T; N]>;
}

impl<T> *const [T] {
    pub const fn as_array<const N: usize>(self) -> Option<*const [T; N]>;
}

impl<T> *mut [T] {
    pub const fn as_mut_array<const N: usize>(self) -> Option<*mut [T; N]>;
}

// alloc::boxed

impl<T> Box<[T]> {
    pub fn into_array<const N: usize>(self) -> Result<Box<[T; N]>, Self>;
}

// alloc::rc

impl<T> Rc<[T]> {
    pub fn into_array<const N: usize>(self) -> Result<Rc<[T; N]>, Self>;
}

// alloc::sync

impl<T> Arc<[T]> {
    pub fn into_array<const N: usize>(self) -> Result<Arc<[T; N]>, Self>;
}

Steps / History

• API change proposal (ACP): #496
• Implementation:
  • ... for [_], *const [_], and *mut [_]: Add as_array and as_mut_array conversion methods to slices. #133512
  • Fix docs for <[_]>::as_array: Fix docs for <[T]>::as_array. #133743
  • Implementation for Box<[_]>, Rc<[_]>, and Arc<[_]>: Add into_array conversion destructors for Box, Rc, and Arc. #134379
  • Reimplementation for using Result in Box<[_]>, Rc<[_]>, and Arc<[_]>
• Final comment period (FCP):
  • ... for [_], *const [_], and *mut [_]
  • ... for Box<[_]>, Rc<[_]>, and Arc<[_]>
• Stabilisation:
  • Stabilisation of [_], *const [_], and *mut [_]: Stabilise as_array in [_] and *const [_]; stabilise as_mut_array in [_] and *mut [_]. #147540
  • Stabilisation of Box<[_]>, Rc<[_]>, and Arc<[_]>

Unresolved Questions

• const-compatibility for the non-primitive types?
• Option or Result for the owning conversions? : Result
• Implementations for Mutex and RwLock?
• Vec::into_boxed_array?
• str::as_bytes_array and String::into_boxed_bytes_array?

[bjoernager]

@RustyYato suggests the following signature for the alloc-typed slices:

pub fn into_array<const N: usize>(self) -> Result<Self<[T; N]>, Self<[T]>>;

to prevent accidental leaks if conversion fails. Would this be preferred as-is or would a new error type (e.g. SliceIntoArrayError) have to be defined?

[programmerjake]

well, if you use Rc::<dyn Any>::downcast as precedence, just returning Result<Rc<[T; N]>, Rc<[T]>> (and likewise for other owning types) should be good imo

[bjoernager]

It seems I messed up the docs entry for <[T]>::as_array. I'll make a follow-up PR addressing this when I can.

[bjoernager]

I am aware that they mostly do not specialise any methods, but could (and should) we extend this to also include Mutex and RwLock?