# 1.25.0[−][src]Struct core::ptr::NonNull

    #[repr(transparent)]pub struct NonNull<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: Sized> NonNull<T>`[src]

#### `pub const fn dangling() -> Self` 1.25.0 (const: 1.32.0)[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: ?Sized> NonNull<T>`[src]

#### `pub const unsafe fn new_unchecked(ptr: *mut T) -> Self` 1.25.0 (const: 1.32.0)[src]

Creates a new `NonNull`.

# Safety

`ptr` must be non-null.

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

Creates a new `NonNull` if `ptr` is non-null.

#### `pub const fn as_ptr(self) -> *mut T` 1.25.0 (const: 1.32.0)[src]

Acquires the underlying `*mut` pointer.

#### `pub unsafe fn as_ref(&self) -> &T`[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`[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 (const: 1.32.0)[src]

Casts to a pointer of another type.

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

#### `pub fn slice_from_raw_parts(data: NonNull<T>, len: usize) -> Self`[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>]`[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>]`[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::{Allocator, Layout, Global};
    use std::mem::MaybeUninit;
    use std::ptr::NonNull;

    let memory: NonNull<[u8]> = Global.allocate(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::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: ?Sized> Clone for NonNull<T>`[src]

#### `pub fn clone(&self) -> Self`[src]

Returns a copy of the value. Read more

#### `pub fn clone_from(&mut self, source: &Self)`1.0.0[src]

Performs copy-assignment from `source`. Read more

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

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

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

#### `pub fn fmt(&self, f: &mut Formatter<'_>) -> Result`[src]

Formats the value using the given formatter. Read more

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

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

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

#### `pub fn from(reference: &T) -> Self`[src]

Performs the conversion.

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

#### `pub fn from(reference: &mut T) -> Self`[src]

Performs the conversion.

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

#### `pub fn hash<H: Hasher>(&self, state: &mut H)`[src]

Feeds this value into the given `Hasher`. Read more

#### `pub fn hash_slice<H: Hasher>(data: &[Self], state: &mut H) where
Self: Sized,` 1.3.0[src]

Feeds a slice of this type into the given `Hasher`. Read more

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

#### `pub fn cmp(&self, other: &Self) -> Ordering`[src]

This method returns an `Ordering` between `self` and `other`. Read more

#### `#[must_use]pub fn max(self, other: Self) -> Self where
Self: Sized,` 1.21.0[src]

Compares and returns the maximum of two values. Read more

#### `#[must_use]pub fn min(self, other: Self) -> Self where
Self: Sized,` 1.21.0[src]

Compares and returns the minimum of two values. Read more

#### `#[must_use]pub fn clamp(self, min: Self, max: Self) -> Self where
Self: Sized,` 1.50.0[src]

Restrict a value to a certain interval. Read more

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

#### `pub fn eq(&self, other: &Self) -> bool`[src]

This method tests for `self` and `other` values to be equal, and is used by `==`. Read more

#### `#[must_use]pub fn ne(&self, other: &Rhs) -> bool` 1.0.0[src]

This method tests for `!=`.

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

#### `pub fn partial_cmp(&self, other: &Self) -> Option<Ordering>`[src]

This method returns an ordering between `self` and `other` values if one exists. Read more

#### `#[must_use]pub fn lt(&self, other: &Rhs) -> bool` 1.0.0[src]

This method tests less than (for `self` and `other`) and is used by the `<` operator. Read more

#### `#[must_use]pub fn le(&self, other: &Rhs) -> bool` 1.0.0[src]

This method tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more

#### `#[must_use]pub fn gt(&self, other: &Rhs) -> bool` 1.0.0[src]

This method tests greater than (for `self` and `other`) and is used by the `>` operator. Read more

#### `#[must_use]pub fn ge(&self, other: &Rhs) -> bool` 1.0.0[src]

This method tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more

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

#### `pub fn fmt(&self, f: &mut Formatter<'_>) -> Result`[src]

Formats the value using the given formatter.

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

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

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

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

## Auto Trait Implementations

### `impl<T: ?Sized> Unpin for NonNull<T>`[src]

## Blanket Implementations

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

#### `pub fn type_id(&Self) -> TypeId`[src]

Gets the `TypeId` of `self`. Read more

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

#### `pub fn borrow(&Self) -> &T`[src]

Immutably borrows from an owned value. Read more

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

#### `pub fn borrow_mut(&mut Self) -> &mut T`[src]

Mutably borrows from an owned value. Read more

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

#### `pub fn from(T) -> T`[src]

Performs the conversion.

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

#### `pub fn into(Self) -> U`[src]

Performs the conversion.

### `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.

#### `pub fn try_from(U) -> Result<T, <T as TryFrom<U>>::Error>`[src]

Performs the conversion.

### `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.

#### `pub fn try_into(Self) -> Result<U, <U as TryFrom<T>>::Error>`[src]

Performs the conversion.