Trait Pointable

pub trait Pointable {
    type Init;

    const ALIGN: usize;

    // Required methods
    unsafe fn init(init: Self::Init) -> usize;
    unsafe fn deref<'a>(ptr: usize) -> &'a Self;
    unsafe fn deref_mut<'a>(ptr: usize) -> &'a mut Self;
    unsafe fn drop(ptr: usize);
}

Types that are pointed to by a single word.

In concurrent programming, it is necessary to represent an object within a word because atomic operations (e.g., reads, writes, read-modify-writes) support only single words. This trait qualifies such types that are pointed to by a single word.

The trait generalizes Box<T> for a sized type T. In a box, an object of type T is allocated in heap and it is owned by a single-word pointer. This trait is also implemented for [MaybeUninit<T>] by storing its size along with its elements and pointing to the pair of array size and elements.

Pointers to Pointable types can be stored in Atomic, Owned, and Shared. In particular, Crossbeam supports dynamically sized slices as follows.

use std::mem::MaybeUninit;
use crossbeam_epoch::Owned;

let o = Owned::<[MaybeUninit<i32>]>::init(10); // allocating [i32; 10]

Required Associated Constants

const ALIGN: usize

The alignment of pointer.

Required Associated Types

type Init

The type for initializers.

Required Methods

unsafe fn init(init: Self::Init) -> usize

Initializes a with the given initializer.

Safety

The result should be a multiple of ALIGN.

unsafe fn deref<'a>(ptr: usize) -> &'a Self

Dereferences the given pointer.

Safety

• The given ptr should have been initialized with Pointable::init.
• ptr should not have yet been dropped by Pointable::drop.
• ptr should not be mutably dereferenced by Pointable::deref_mut concurrently.

unsafe fn deref_mut<'a>(ptr: usize) -> &'a mut Self

Mutably dereferences the given pointer.

Safety

• The given ptr should have been initialized with Pointable::init.
• ptr should not have yet been dropped by Pointable::drop.
• ptr should not be dereferenced by Pointable::deref or Pointable::deref_mut concurrently.

unsafe fn drop(ptr: usize)

Drops the object pointed to by the given pointer.

Safety

• The given ptr should have been initialized with Pointable::init.
• ptr should not have yet been dropped by Pointable::drop.
• ptr should not be dereferenced by Pointable::deref or Pointable::deref_mut concurrently.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementations on Foreign Types

impl<T> Pointable for [MaybeUninit<T>]

const ALIGN: usize

type Init = usize

unsafe fn init(len: Self::Init) -> usize

unsafe fn deref<'a>(ptr: usize) -> &'a Self

unsafe fn deref_mut<'a>(ptr: usize) -> &'a mut Self

unsafe fn drop(ptr: usize)

Implementors

impl<T> Pointable for T

const ALIGN: usize

type Init = T