Struct bevy_ptr::ConstNonNull

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pub struct ConstNonNull<T: ?Sized>(/* private fields */);

Expand description

A newtype around NonNull that only allows conversion to read-only borrows or pointers.

This type can be thought of as the *const T to NonNull<T>’s *mut T.

Implementations§

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impl<T: ?Sized> ConstNonNull<T>

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pub fn new(ptr: *const T) -> Option<Self>

Creates a new ConstNonNull if ptr is non-null.

§Examples

use bevy_ptr::ConstNonNull;

let x = 0u32;
let ptr = ConstNonNull::<u32>::new(&x as *const _).expect("ptr is null!");

if let Some(ptr) = ConstNonNull::<u32>::new(std::ptr::null()) {
    unreachable!();
}

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pub const unsafe fn new_unchecked(ptr: *const T) -> Self

Creates a new ConstNonNull.

§Safety

ptr must be non-null.

§Examples

use bevy_ptr::ConstNonNull;

let x = 0u32;
let ptr = unsafe { ConstNonNull::new_unchecked(&x as *const _) };

Incorrect usage of this function:

use bevy_ptr::ConstNonNull;

// NEVER DO THAT!!! This is undefined behavior. ⚠️
let ptr = unsafe { ConstNonNull::<u32>::new_unchecked(std::ptr::null()) };

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pub unsafe fn as_ref<'a>(&self) -> &'a T

Returns a shared reference to the value.

§Safety

When calling this method, you have to ensure that all of the following is true:

The pointer must be properly aligned.
It must be “dereferenceable” in the sense defined in the module documentation.
The pointer must point to an initialized instance of T.
You must enforce Rust’s aliasing rules, since the returned lifetime 'a is arbitrarily chosen and does not necessarily reflect the actual lifetime of the data. In particular, while this reference exists, the memory the pointer points to must not get mutated (except inside UnsafeCell).

This applies even if the result of this method is unused! (The part about being initialized is not yet fully decided, but until it is, the only safe approach is to ensure that they are indeed initialized.)

§Examples

use bevy_ptr::ConstNonNull;

let mut x = 0u32;
let ptr = ConstNonNull::new(&mut x as *mut _).expect("ptr is null!");

let ref_x = unsafe { ptr.as_ref() };
println!("{ref_x}");