Tracking Issue for `mem::Alignment` type

[scottmcm]

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Feature gate: #![feature(ptr_alignment_type)]

This is a tracking issue for the ptr::Alignment type, and related methods, to represent values that are valid alignments in the rust abstract machine.

Public API

// core::ptr

#[derive(Copy, Clone, Eq, PartialEq)]
pub struct Alignment(…);

impl Debug for Alignment;
impl Ord for Alignment;
impl PartialOrd for Alignment;
impl Hash for Alignment;

impl Alignment {
    pub const MIN: Self;
    pub const fn of<T>() -> Self;
    pub const fn new(align: usize) -> Option<Self>;
    pub const unsafe fn new_unchecked(align: usize) -> Self;
    pub const fn as_usize(self) -> usize;
    pub const fn as_nonzero(self) -> NonZeroUsize;
    pub const fn log2(self) -> u32;
}

impl TryFrom<NonZeroUsize> for Alignment;
impl TryFrom<usize> for Alignment;
impl From<Alignment> for NonZeroUsize;
impl From<Alignment> for usize;

Steps / History

• ACP Add a specific type for pointer alignment libs-team#108
• Implementation: Add ptr::Alignment type #102072
• From<Alignment> for usize & NonZeroUsize #102862
• Final comment period (FCP)¹
• Stabilization PR

Unresolved Questions

• Is the mask method (from impl more traits for ptr::Alignment, add mask method #115249) correct? Should it be !(a - 1) or a - 1? Should it have a different name to distinguish it more from <*const _>::mask?

Footnotes

1. https://std-dev-guide.rust-lang.org/feature-lifecycle/stabilization.html ↩

[kupiakos]

I've been able to take advantage of an alignment newtype for performance in an embedded arena library and would find this useful to be stabilized. Are there any blockers for an FCP?