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) -> Option<Box<[T; N]>>;
}

// alloc::rc

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

// alloc::sync

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

Steps / History

• API change proposal (ACP): #496
• Implementation for [T], *const [T], and *mut [T]: Add as_array and as_mut_array conversion methods to slices. #133512
• Fix docs for <[T]>::as_array: Fix docs for <[T]>::as_array. #133743
• Implementation for Box<[T]>, Rc<[T]>, and Arc<[T]>: Add into_array conversion destructors for Box, Rc, and Arc. #134379
• Final comment period (FCP)
• Stabilization PR

Unresolved Questions

• const-compatible for the non-primitive types?
• Option or Result for the owning conversions?
• Implementation for Mutex and RwLock?

[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]

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