Struct wasmer_types::entity::__core::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>

pub const fn dangling() -> NonNull<T>

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.

impl<T> NonNull<T> where
    T: ?Sized, 

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

Creates a new NonNull.

Safety

ptr must be non-null.

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

Creates a new NonNull if ptr is non-null.

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

Acquires the underlying *mut pointer.

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

Dereferences the content.

The resulting lifetime is bound to self so this behaves "as if" it were actually an instance of T that is getting borrowed. If a longer (unbound) lifetime is needed, use &*my_ptr.as_ptr().

Safety

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

• self is properly aligned
• self must point to an initialized instance of T; in particular, the pointer must be "dereferencable" in the sense defined here.

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.)

Additionally, the lifetime of self does not necessarily reflect the actual lifetime of the data. You must enforce Rust's aliasing rules. In particular, for the duration of this lifetime, the memory the pointer points to must not get mutated (except inside UnsafeCell).

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

Mutably dereferences the content.

The resulting lifetime is bound to self so this behaves "as if" it were actually an instance of T that is getting borrowed. If a longer (unbound) lifetime is needed, use &mut *my_ptr.as_ptr().

Safety

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

• self is properly aligned
• self must point to an initialized instance of T; in particular, the pointer must be "dereferenceable" in the sense defined here.

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.)

Additionally, the lifetime of self does not necessarily reflect the actual lifetime of the data. You must enforce Rust's aliasing rules. In particular, for the duration of this lifetime, the memory this pointer points to must not get accessed (read or written) through any other pointer.

pub const fn cast<U>(self) -> NonNull<U>

Casts to a pointer of another type.

impl<T> NonNull<[T]>

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

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

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);

(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 const fn len(self) -> usize

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

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);

pub const fn as_non_null_ptr(self) -> NonNull<T>

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

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());

pub const fn as_mut_ptr(self) -> *mut T

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

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);

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

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

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));
}

Trait Implementations

impl<T> Clone for NonNull<T> where
    T: ?Sized, 

fn clone(&self) -> NonNull<T>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T> Copy for NonNull<T> where
    T: ?Sized, 

impl<T> Debug for NonNull<T> where
    T: ?Sized, 

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl<T> Eq for NonNull<T> where
    T: ?Sized, 

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

fn from(reference: &T) -> NonNull<T>

Performs the conversion.

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

fn from(reference: &mut T) -> NonNull<T>

Performs the conversion.

impl<T> From<Unique<T>> for NonNull<T> where
    T: ?Sized, 

fn from(unique: Unique<T>) -> NonNull<T>

Performs the conversion.

impl<T> Hash for NonNull<T> where
    T: ?Sized, 

fn hash<H>(&self, state: &mut H) where
    H: Hasher, 

Feeds this value into the given [Hasher].

fn hash_slice<H>(data: &[Self], state: &mut H) where
    H: Hasher, 

Feeds a slice of this type into the given [Hasher].

impl<T> Ord for NonNull<T> where
    T: ?Sized, 

fn cmp(&self, other: &NonNull<T>) -> Ordering

This method returns an [Ordering] between self and other.

#[must_use]fn max(self, other: Self) -> Self

Compares and returns the maximum of two values.

#[must_use]fn min(self, other: Self) -> Self

Compares and returns the minimum of two values.

#[must_use]fn clamp(self, min: Self, max: Self) -> Self

🔬 This is a nightly-only experimental API. (clamp)

Restrict a value to a certain interval.

impl<T> PartialEq<NonNull<T>> for NonNull<T> where
    T: ?Sized, 

fn eq(&self, other: &NonNull<T>) -> bool

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

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

This method tests for !=.

impl<T> PartialOrd<NonNull<T>> for NonNull<T> where
    T: ?Sized, 

fn partial_cmp(&self, other: &NonNull<T>) -> Option<Ordering>

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

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

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

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

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

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

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

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

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

impl<T> Pointer for NonNull<T> where
    T: ?Sized, 

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl<T> !Send for NonNull<T> where
    T: ?Sized, 

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

impl<T> !Sync for NonNull<T> where
    T: ?Sized, 

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

impl<T> UnwindSafe for NonNull<T> where
    T: RefUnwindSafe + ?Sized,