1.25.0[][src]Struct std::ptr::NonNull

#[repr(transparent)]pub struct NonNull<T> where
    T: ?Sized
{ /* fields omitted */ }

*mut T but non-zero and covariant.

This is often the correct thing to use when building data structures using raw pointers, but is ultimately more dangerous to use because of its additional properties. If you're not sure if you should use NonNull<T>, just use *mut T!

Unlike *mut T, the pointer must always be non-null, even if the pointer is never dereferenced. This is so that enums may use this forbidden value as a discriminant -- Option<NonNull<T>> has the same size as *mut T. However the pointer may still dangle if it isn't dereferenced.

Unlike *mut T, NonNull<T> is covariant over T. If this is incorrect for your use case, you should include some PhantomData in your type to provide invariance, such as PhantomData<Cell<T>> or PhantomData<&'a mut T>. Usually this won't be necessary; covariance is correct for most safe abstractions, such as Box, Rc, Arc, Vec, and LinkedList. This is the case because they provide a public API that follows the normal shared XOR mutable rules of Rust.

Notice that NonNull<T> has a From instance for &T. However, this does not change the fact that mutating through a (pointer derived from a) shared reference is undefined behavior unless the mutation happens inside an UnsafeCell<T>. The same goes for creating a mutable reference from a shared reference. When using this From instance without an UnsafeCell<T>, it is your responsibility to ensure that as_mut is never called, and as_ptr is never used for mutation.

Implementations

impl<T> NonNull<T>[src]

pub const fn dangling() -> NonNull<T>[src]

Creates a new NonNull that is dangling, but well-aligned.

This is useful for initializing types which lazily allocate, like Vec::new does.

Note that the pointer value may potentially represent a valid pointer to a T, which means this must not be used as a "not yet initialized" sentinel value. Types that lazily allocate must track initialization by some other means.

pub unsafe fn as_uninit_ref(&self) -> &MaybeUninit<T>[src]

🔬 This is a nightly-only experimental API. (ptr_as_uninit #75402)

Returns a shared references to the value. In contrast to as_ref, this does not require that the value has to be initialized.

For the mutable counterpart see as_uninit_mut.

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 "dereferencable" in the sense defined in the module documentation.

  • 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, for the duration of this lifetime, the memory the pointer points to must not get mutated (except inside UnsafeCell).

This applies even if the result of this method is unused!

pub unsafe fn as_uninit_mut(&mut self) -> &mut MaybeUninit<T>[src]

🔬 This is a nightly-only experimental API. (ptr_as_uninit #75402)

Returns a unique references to the value. In contrast to as_mut, this does not require that the value has to be initialized.

For the shared counterpart see as_uninit_ref.

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 "dereferencable" in the sense defined in the module documentation.

  • 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, for the duration of this lifetime, the memory the pointer points to must not get accessed (read or written) through any other pointer.

This applies even if the result of this method is unused!

impl<T> NonNull<T> where
    T: ?Sized
[src]

pub const unsafe fn new_unchecked(ptr: *mut T) -> NonNull<T>[src]

Creates a new NonNull.

Safety

ptr must be non-null.

pub fn new(ptr: *mut T) -> Option<NonNull<T>>[src]

Creates a new NonNull if ptr is non-null.

pub const fn as_ptr(self) -> *mut T[src]

Acquires the underlying *mut pointer.

pub unsafe fn as_ref(&self) -> &T

Notable traits for &'_ mut F

impl<'_, F> Future for &'_ mut F where
    F: Unpin + Future + ?Sized
type Output = <F as Future>::Output;impl<'_, I> Iterator for &'_ mut I where
    I: Iterator + ?Sized
type Item = <I as Iterator>::Item;impl<R: Read + ?Sized, '_> Read for &'_ mut Rimpl<W: Write + ?Sized, '_> Write for &'_ mut W
[src]

Returns a shared reference to the value. If the value may be uninitialized, as_uninit_ref must be used instead.

For the mutable counterpart see as_mut.

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 "dereferencable" 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, for the duration of this lifetime, 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.)

pub unsafe fn as_mut(&mut self) -> &mut T

Notable traits for &'_ mut F

impl<'_, F> Future for &'_ mut F where
    F: Unpin + Future + ?Sized
type Output = <F as Future>::Output;impl<'_, I> Iterator for &'_ mut I where
    I: Iterator + ?Sized
type Item = <I as Iterator>::Item;impl<R: Read + ?Sized, '_> Read for &'_ mut Rimpl<W: Write + ?Sized, '_> Write for &'_ mut W
[src]

Returns a unique reference to the value. If the value may be uninitialized, as_uninit_mut must be used instead.

For the shared counterpart see as_ref.

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 "dereferencable" 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, for the duration of this lifetime, the memory the pointer points to must not get accessed (read or written) through any other pointer.

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.)

pub const fn cast<U>(self) -> NonNull<U>1.27.0[src]

Casts to a pointer of another type.

impl<T> NonNull<[T]>[src]

pub fn slice_from_raw_parts(data: NonNull<T>, len: usize) -> NonNull<[T]>[src]

🔬 This is a nightly-only experimental API. (nonnull_slice_from_raw_parts #71941)

Creates a non-null raw slice from a thin pointer and a length.

The len argument is the number of elements, not the number of bytes.

This function is safe, but dereferencing the return value is unsafe. See the documentation of slice::from_raw_parts for slice safety requirements.

Examples

#![feature(nonnull_slice_from_raw_parts)]

use std::ptr::NonNull;

// create a slice pointer when starting out with a pointer to the first element
let mut x = [5, 6, 7];
let nonnull_pointer = NonNull::new(x.as_mut_ptr()).unwrap();
let slice = NonNull::slice_from_raw_parts(nonnull_pointer, 3);
assert_eq!(unsafe { slice.as_ref()[2] }, 7);
Run

(Note that this example artificially demonstrates a use of this method, but let slice = NonNull::from(&x[..]); would be a better way to write code like this.)

pub fn len(self) -> usize[src]

🔬 This is a nightly-only experimental API. (slice_ptr_len #71146)

Returns the length of a non-null raw slice.

The returned value is the number of elements, not the number of bytes.

This function is safe, even when the non-null raw slice cannot be dereferenced to a slice because the pointer does not have a valid address.

Examples

#![feature(slice_ptr_len, nonnull_slice_from_raw_parts)]
use std::ptr::NonNull;

let slice: NonNull<[i8]> = NonNull::slice_from_raw_parts(NonNull::dangling(), 3);
assert_eq!(slice.len(), 3);
Run

pub fn as_non_null_ptr(self) -> NonNull<T>[src]

🔬 This is a nightly-only experimental API. (slice_ptr_get #74265)

Returns a non-null pointer to the slice's buffer.

Examples

#![feature(slice_ptr_get, nonnull_slice_from_raw_parts)]
use std::ptr::NonNull;

let slice: NonNull<[i8]> = NonNull::slice_from_raw_parts(NonNull::dangling(), 3);
assert_eq!(slice.as_non_null_ptr(), NonNull::new(1 as *mut i8).unwrap());
Run

pub fn as_mut_ptr(self) -> *mut T[src]

🔬 This is a nightly-only experimental API. (slice_ptr_get #74265)

Returns a raw pointer to the slice's buffer.

Examples

#![feature(slice_ptr_get, nonnull_slice_from_raw_parts)]
use std::ptr::NonNull;

let slice: NonNull<[i8]> = NonNull::slice_from_raw_parts(NonNull::dangling(), 3);
assert_eq!(slice.as_mut_ptr(), 1 as *mut i8);
Run

pub unsafe fn as_uninit_slice(&self) -> &[MaybeUninit<T>]

Notable traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]
[src]

🔬 This is a nightly-only experimental API. (ptr_as_uninit #75402)

Returns a shared reference to a slice of possibly uninitialized values. In contrast to as_ref, this does not require that the value has to be initialized.

For the mutable counterpart see as_uninit_slice_mut.

Safety

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

  • The pointer must be valid for reads for ptr.len() * mem::size_of::<T>() many bytes, and it must be properly aligned. This means in particular:

    • The entire memory range of this slice must be contained within a single allocated object! Slices can never span across multiple allocated objects.

    • The pointer must be aligned even for zero-length slices. One reason for this is that enum layout optimizations may rely on references (including slices of any length) being aligned and non-null to distinguish them from other data. You can obtain a pointer that is usable as data for zero-length slices using NonNull::dangling().

  • The total size ptr.len() * mem::size_of::<T>() of the slice must be no larger than isize::MAX. See the safety documentation of pointer::offset.

  • 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, for the duration of this lifetime, the memory the pointer points to must not get mutated (except inside UnsafeCell).

This applies even if the result of this method is unused!

See also slice::from_raw_parts.

pub unsafe fn as_uninit_slice_mut(&self) -> &mut [MaybeUninit<T>]

Notable traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]
[src]

🔬 This is a nightly-only experimental API. (ptr_as_uninit #75402)

Returns a unique reference to a slice of possibly uninitialized values. In contrast to as_mut, this does not require that the value has to be initialized.

For the shared counterpart see as_uninit_slice.

Safety

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

  • The pointer must be valid for reads and writes for ptr.len() * mem::size_of::<T>() many bytes, and it must be properly aligned. This means in particular:

    • The entire memory range of this slice must be contained within a single allocated object! Slices can never span across multiple allocated objects.

    • The pointer must be aligned even for zero-length slices. One reason for this is that enum layout optimizations may rely on references (including slices of any length) being aligned and non-null to distinguish them from other data. You can obtain a pointer that is usable as data for zero-length slices using NonNull::dangling().

  • The total size ptr.len() * mem::size_of::<T>() of the slice must be no larger than isize::MAX. See the safety documentation of pointer::offset.

  • 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, for the duration of this lifetime, the memory the pointer points to must not get accessed (read or written) through any other pointer.

This applies even if the result of this method is unused!

See also slice::from_raw_parts_mut.

Examples

#![feature(allocator_api, ptr_as_uninit)]

use std::alloc::{AllocRef, Layout, Global};
use std::mem::MaybeUninit;
use std::ptr::NonNull;

let memory: NonNull<[u8]> = Global.alloc(Layout::new::<[u8; 32]>())?;
// This is safe as `memory` is valid for reads and writes for `memory.len()` many bytes.
// Note that calling `memory.as_mut()` is not allowed here as the content may be uninitialized.
let slice: &mut [MaybeUninit<u8>] = unsafe { memory.as_uninit_slice_mut() };
Run

pub unsafe fn get_unchecked_mut<I>(
    self,
    index: I
) -> NonNull<<I as SliceIndex<[T]>>::Output> where
    I: SliceIndex<[T]>, 
[src]

🔬 This is a nightly-only experimental API. (slice_ptr_get #74265)

Returns a raw pointer to an element or subslice, without doing bounds checking.

Calling this method with an out-of-bounds index or when self is not dereferencable is undefined behavior even if the resulting pointer is not used.

Examples

#![feature(slice_ptr_get, nonnull_slice_from_raw_parts)]
use std::ptr::NonNull;

let x = &mut [1, 2, 4];
let x = NonNull::slice_from_raw_parts(NonNull::new(x.as_mut_ptr()).unwrap(), x.len());

unsafe {
    assert_eq!(x.get_unchecked_mut(1).as_ptr(), x.as_non_null_ptr().as_ptr().add(1));
}
Run

Trait Implementations

impl<T> Clone for NonNull<T> where
    T: ?Sized
[src]

impl<T, U> CoerceUnsized<NonNull<U>> for NonNull<T> where
    T: Unsize<U> + ?Sized,
    U: ?Sized
[src]

impl<T> Copy for NonNull<T> where
    T: ?Sized
[src]

impl<T> Debug for NonNull<T> where
    T: ?Sized
[src]

impl<T, U> DispatchFromDyn<NonNull<U>> for NonNull<T> where
    T: Unsize<U> + ?Sized,
    U: ?Sized
[src]

impl<T> Eq for NonNull<T> where
    T: ?Sized
[src]

impl<'_, T> From<&'_ T> for NonNull<T> where
    T: ?Sized
[src]

impl<'_, T> From<&'_ mut T> for NonNull<T> where
    T: ?Sized
[src]

impl<T> From<Unique<T>> for NonNull<T> where
    T: ?Sized
[src]

impl<T> Hash for NonNull<T> where
    T: ?Sized
[src]

impl<T> Ord for NonNull<T> where
    T: ?Sized
[src]

impl<T> PartialEq<NonNull<T>> for NonNull<T> where
    T: ?Sized
[src]

impl<T> PartialOrd<NonNull<T>> for NonNull<T> where
    T: ?Sized
[src]

impl<T> Pointer for NonNull<T> where
    T: ?Sized
[src]

impl<T> !Send for NonNull<T> where
    T: ?Sized
[src]

NonNull pointers are not Send because the data they reference may be aliased.

impl<T> !Sync for NonNull<T> where
    T: ?Sized
[src]

NonNull pointers are not Sync because the data they reference may be aliased.

impl<T: RefUnwindSafe + ?Sized> UnwindSafe for NonNull<T>[src]

Auto Trait Implementations

impl<T: ?Sized> RefUnwindSafe for NonNull<T> where
    T: RefUnwindSafe

impl<T: ?Sized> Unpin for NonNull<T>

Blanket Implementations

impl<T> Any for T where
    T: 'static + ?Sized
[src]

impl<T> Borrow<T> for T where
    T: ?Sized
[src]

impl<T> BorrowMut<T> for T where
    T: ?Sized
[src]

impl<T> From<T> for T[src]

impl<T, U> Into<U> for T where
    U: From<T>, 
[src]

impl<T> ToOwned for T where
    T: Clone
[src]

type Owned = T

The resulting type after obtaining ownership.

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 
[src]

type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 
[src]

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.