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|
use crate::cmp::Ordering;
use crate::convert::From;
use crate::fmt;
use crate::hash;
use crate::intrinsics::assert_unsafe_precondition;
use crate::marker::Unsize;
use crate::mem::{self, MaybeUninit};
use crate::num::NonZeroUsize;
use crate::ops::{CoerceUnsized, DispatchFromDyn};
use crate::ptr::Unique;
use crate::slice::{self, SliceIndex};
/// `*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>` was chosen to be covariant over `T`. This makes it
/// possible to use `NonNull<T>` when building covariant types, but introduces the
/// risk of unsoundness if used in a type that shouldn't actually be covariant.
/// (The opposite choice was made for `*mut T` even though technically the unsoundness
/// could only be caused by calling unsafe functions.)
///
/// 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.
///
/// If your type cannot safely be covariant, you must ensure it contains some
/// additional field to provide invariance. Often this field will be a [`PhantomData`]
/// type like `PhantomData<Cell<T>>` or `PhantomData<&'a mut T>`.
///
/// 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.
///
/// [covariant]: https://doc.rust-lang.org/reference/subtyping.html
/// [`PhantomData`]: crate::marker::PhantomData
/// [`UnsafeCell<T>`]: crate::cell::UnsafeCell
#[stable(feature = "nonnull", since = "1.25.0")]
#[repr(transparent)]
#[rustc_layout_scalar_valid_range_start(1)]
#[rustc_nonnull_optimization_guaranteed]
pub struct NonNull<T: ?Sized> {
pointer: *const T,
}
/// `NonNull` pointers are not `Send` because the data they reference may be aliased.
// N.B., this impl is unnecessary, but should provide better error messages.
#[stable(feature = "nonnull", since = "1.25.0")]
impl<T: ?Sized> !Send for NonNull<T> {}
/// `NonNull` pointers are not `Sync` because the data they reference may be aliased.
// N.B., this impl is unnecessary, but should provide better error messages.
#[stable(feature = "nonnull", since = "1.25.0")]
impl<T: ?Sized> !Sync for NonNull<T> {}
impl<T: Sized> 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.
///
/// # Examples
///
/// ```
/// use std::ptr::NonNull;
///
/// let ptr = NonNull::<u32>::dangling();
/// // Important: don't try to access the value of `ptr` without
/// // initializing it first! The pointer is not null but isn't valid either!
/// ```
#[stable(feature = "nonnull", since = "1.25.0")]
#[rustc_const_stable(feature = "const_nonnull_dangling", since = "1.36.0")]
#[must_use]
#[inline]
pub const fn dangling() -> Self {
// SAFETY: mem::align_of() returns a non-zero usize which is then casted
// to a *mut T. Therefore, `ptr` is not null and the conditions for
// calling new_unchecked() are respected.
unsafe {
let ptr = crate::ptr::invalid_mut::<T>(mem::align_of::<T>());
NonNull::new_unchecked(ptr)
}
}
/// 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`].
///
/// [`as_ref`]: NonNull::as_ref
/// [`as_uninit_mut`]: NonNull::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 "dereferenceable" 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, 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 module documentation]: crate::ptr#safety
#[inline]
#[must_use]
#[unstable(feature = "ptr_as_uninit", issue = "75402")]
#[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
pub const unsafe fn as_uninit_ref<'a>(self) -> &'a MaybeUninit<T> {
// SAFETY: the caller must guarantee that `self` meets all the
// requirements for a reference.
unsafe { &*self.cast().as_ptr() }
}
/// 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`].
///
/// [`as_mut`]: NonNull::as_mut
/// [`as_uninit_ref`]: NonNull::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 "dereferenceable" 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, while this reference exists, 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 module documentation]: crate::ptr#safety
#[inline]
#[must_use]
#[unstable(feature = "ptr_as_uninit", issue = "75402")]
#[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
pub const unsafe fn as_uninit_mut<'a>(self) -> &'a mut MaybeUninit<T> {
// SAFETY: the caller must guarantee that `self` meets all the
// requirements for a reference.
unsafe { &mut *self.cast().as_ptr() }
}
}
impl<T: ?Sized> NonNull<T> {
/// Creates a new `NonNull`.
///
/// # Safety
///
/// `ptr` must be non-null.
///
/// # Examples
///
/// ```
/// use std::ptr::NonNull;
///
/// let mut x = 0u32;
/// let ptr = unsafe { NonNull::new_unchecked(&mut x as *mut _) };
/// ```
///
/// *Incorrect* usage of this function:
///
/// ```rust,no_run
/// use std::ptr::NonNull;
///
/// // NEVER DO THAT!!! This is undefined behavior. ⚠️
/// let ptr = unsafe { NonNull::<u32>::new_unchecked(std::ptr::null_mut()) };
/// ```
#[stable(feature = "nonnull", since = "1.25.0")]
#[rustc_const_stable(feature = "const_nonnull_new_unchecked", since = "1.25.0")]
#[inline]
pub const unsafe fn new_unchecked(ptr: *mut T) -> Self {
// SAFETY: the caller must guarantee that `ptr` is non-null.
unsafe {
assert_unsafe_precondition!("NonNull::new_unchecked requires that the pointer is non-null", [T: ?Sized](ptr: *mut T) => !ptr.is_null());
NonNull { pointer: ptr as _ }
}
}
/// Creates a new `NonNull` if `ptr` is non-null.
///
/// # Examples
///
/// ```
/// use std::ptr::NonNull;
///
/// let mut x = 0u32;
/// let ptr = NonNull::<u32>::new(&mut x as *mut _).expect("ptr is null!");
///
/// if let Some(ptr) = NonNull::<u32>::new(std::ptr::null_mut()) {
/// unreachable!();
/// }
/// ```
#[stable(feature = "nonnull", since = "1.25.0")]
#[rustc_const_unstable(feature = "const_nonnull_new", issue = "93235")]
#[inline]
pub const fn new(ptr: *mut T) -> Option<Self> {
if !ptr.is_null() {
// SAFETY: The pointer is already checked and is not null
Some(unsafe { Self::new_unchecked(ptr) })
} else {
None
}
}
/// Performs the same functionality as [`std::ptr::from_raw_parts`], except that a
/// `NonNull` pointer is returned, as opposed to a raw `*const` pointer.
///
/// See the documentation of [`std::ptr::from_raw_parts`] for more details.
///
/// [`std::ptr::from_raw_parts`]: crate::ptr::from_raw_parts
#[unstable(feature = "ptr_metadata", issue = "81513")]
#[rustc_const_unstable(feature = "ptr_metadata", issue = "81513")]
#[inline]
pub const fn from_raw_parts(
data_address: NonNull<()>,
metadata: <T as super::Pointee>::Metadata,
) -> NonNull<T> {
// SAFETY: The result of `ptr::from::raw_parts_mut` is non-null because `data_address` is.
unsafe {
NonNull::new_unchecked(super::from_raw_parts_mut(data_address.as_ptr(), metadata))
}
}
/// Decompose a (possibly wide) pointer into its address and metadata components.
///
/// The pointer can be later reconstructed with [`NonNull::from_raw_parts`].
#[unstable(feature = "ptr_metadata", issue = "81513")]
#[rustc_const_unstable(feature = "ptr_metadata", issue = "81513")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub const fn to_raw_parts(self) -> (NonNull<()>, <T as super::Pointee>::Metadata) {
(self.cast(), super::metadata(self.as_ptr()))
}
/// Gets the "address" portion of the pointer.
///
/// For more details see the equivalent method on a raw pointer, [`pointer::addr`].
///
/// This API and its claimed semantics are part of the Strict Provenance experiment,
/// see the [`ptr` module documentation][crate::ptr].
#[must_use]
#[inline]
#[unstable(feature = "strict_provenance", issue = "95228")]
pub fn addr(self) -> NonZeroUsize {
// SAFETY: The pointer is guaranteed by the type to be non-null,
// meaning that the address will be non-zero.
unsafe { NonZeroUsize::new_unchecked(self.pointer.addr()) }
}
/// Creates a new pointer with the given address.
///
/// For more details see the equivalent method on a raw pointer, [`pointer::with_addr`].
///
/// This API and its claimed semantics are part of the Strict Provenance experiment,
/// see the [`ptr` module documentation][crate::ptr].
#[must_use]
#[inline]
#[unstable(feature = "strict_provenance", issue = "95228")]
pub fn with_addr(self, addr: NonZeroUsize) -> Self {
// SAFETY: The result of `ptr::from::with_addr` is non-null because `addr` is guaranteed to be non-zero.
unsafe { NonNull::new_unchecked(self.pointer.with_addr(addr.get()) as *mut _) }
}
/// Creates a new pointer by mapping `self`'s address to a new one.
///
/// For more details see the equivalent method on a raw pointer, [`pointer::map_addr`].
///
/// This API and its claimed semantics are part of the Strict Provenance experiment,
/// see the [`ptr` module documentation][crate::ptr].
#[must_use]
#[inline]
#[unstable(feature = "strict_provenance", issue = "95228")]
pub fn map_addr(self, f: impl FnOnce(NonZeroUsize) -> NonZeroUsize) -> Self {
self.with_addr(f(self.addr()))
}
/// Acquires the underlying `*mut` pointer.
///
/// # Examples
///
/// ```
/// use std::ptr::NonNull;
///
/// let mut x = 0u32;
/// let ptr = NonNull::new(&mut x).expect("ptr is null!");
///
/// let x_value = unsafe { *ptr.as_ptr() };
/// assert_eq!(x_value, 0);
///
/// unsafe { *ptr.as_ptr() += 2; }
/// let x_value = unsafe { *ptr.as_ptr() };
/// assert_eq!(x_value, 2);
/// ```
#[stable(feature = "nonnull", since = "1.25.0")]
#[rustc_const_stable(feature = "const_nonnull_as_ptr", since = "1.32.0")]
#[must_use]
#[inline(always)]
pub const fn as_ptr(self) -> *mut T {
self.pointer as *mut T
}
/// 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`].
///
/// [`as_uninit_ref`]: NonNull::as_uninit_ref
/// [`as_mut`]: NonNull::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 "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 std::ptr::NonNull;
///
/// let mut x = 0u32;
/// let ptr = NonNull::new(&mut x as *mut _).expect("ptr is null!");
///
/// let ref_x = unsafe { ptr.as_ref() };
/// println!("{ref_x}");
/// ```
///
/// [the module documentation]: crate::ptr#safety
#[stable(feature = "nonnull", since = "1.25.0")]
#[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
#[must_use]
#[inline(always)]
pub const unsafe fn as_ref<'a>(&self) -> &'a T {
// SAFETY: the caller must guarantee that `self` meets all the
// requirements for a reference.
unsafe { &*self.as_ptr() }
}
/// 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`].
///
/// [`as_uninit_mut`]: NonNull::as_uninit_mut
/// [`as_ref`]: NonNull::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 "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 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.)
/// # Examples
///
/// ```
/// use std::ptr::NonNull;
///
/// let mut x = 0u32;
/// let mut ptr = NonNull::new(&mut x).expect("null pointer");
///
/// let x_ref = unsafe { ptr.as_mut() };
/// assert_eq!(*x_ref, 0);
/// *x_ref += 2;
/// assert_eq!(*x_ref, 2);
/// ```
///
/// [the module documentation]: crate::ptr#safety
#[stable(feature = "nonnull", since = "1.25.0")]
#[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
#[must_use]
#[inline(always)]
pub const unsafe fn as_mut<'a>(&mut self) -> &'a mut T {
// SAFETY: the caller must guarantee that `self` meets all the
// requirements for a mutable reference.
unsafe { &mut *self.as_ptr() }
}
/// Casts to a pointer of another type.
///
/// # Examples
///
/// ```
/// use std::ptr::NonNull;
///
/// let mut x = 0u32;
/// let ptr = NonNull::new(&mut x as *mut _).expect("null pointer");
///
/// let casted_ptr = ptr.cast::<i8>();
/// let raw_ptr: *mut i8 = casted_ptr.as_ptr();
/// ```
#[stable(feature = "nonnull_cast", since = "1.27.0")]
#[rustc_const_stable(feature = "const_nonnull_cast", since = "1.36.0")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub const fn cast<U>(self) -> NonNull<U> {
// SAFETY: `self` is a `NonNull` pointer which is necessarily non-null
unsafe { NonNull::new_unchecked(self.as_ptr() as *mut U) }
}
/// See [`pointer::add`] for semantics and safety requirements.
#[inline]
pub(crate) const unsafe fn add(self, delta: usize) -> Self
where
T: Sized,
{
// SAFETY: We require that the delta stays in-bounds of the object, and
// thus it cannot become null, as that would require wrapping the
// address space, which no legal objects are allowed to do.
// And the caller promised the `delta` is sound to add.
unsafe { NonNull { pointer: self.pointer.add(delta) } }
}
}
impl<T> NonNull<[T]> {
/// 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
///
/// ```rust
/// 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.)
#[stable(feature = "nonnull_slice_from_raw_parts", since = "1.70.0")]
#[rustc_const_unstable(feature = "const_slice_from_raw_parts_mut", issue = "67456")]
#[must_use]
#[inline]
pub const fn slice_from_raw_parts(data: NonNull<T>, len: usize) -> Self {
// SAFETY: `data` is a `NonNull` pointer which is necessarily non-null
unsafe { Self::new_unchecked(super::slice_from_raw_parts_mut(data.as_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
///
/// ```rust
/// use std::ptr::NonNull;
///
/// let slice: NonNull<[i8]> = NonNull::slice_from_raw_parts(NonNull::dangling(), 3);
/// assert_eq!(slice.len(), 3);
/// ```
#[stable(feature = "slice_ptr_len_nonnull", since = "1.63.0")]
#[rustc_const_stable(feature = "const_slice_ptr_len_nonnull", since = "1.63.0")]
#[rustc_allow_const_fn_unstable(const_slice_ptr_len)]
#[must_use]
#[inline]
pub const fn len(self) -> usize {
self.as_ptr().len()
}
/// Returns a non-null pointer to the slice's buffer.
///
/// # Examples
///
/// ```rust
/// #![feature(slice_ptr_get)]
/// use std::ptr::NonNull;
///
/// let slice: NonNull<[i8]> = NonNull::slice_from_raw_parts(NonNull::dangling(), 3);
/// assert_eq!(slice.as_non_null_ptr(), NonNull::<i8>::dangling());
/// ```
#[inline]
#[must_use]
#[unstable(feature = "slice_ptr_get", issue = "74265")]
#[rustc_const_unstable(feature = "slice_ptr_get", issue = "74265")]
pub const fn as_non_null_ptr(self) -> NonNull<T> {
// SAFETY: We know `self` is non-null.
unsafe { NonNull::new_unchecked(self.as_ptr().as_mut_ptr()) }
}
/// Returns a raw pointer to the slice's buffer.
///
/// # Examples
///
/// ```rust
/// #![feature(slice_ptr_get)]
/// use std::ptr::NonNull;
///
/// let slice: NonNull<[i8]> = NonNull::slice_from_raw_parts(NonNull::dangling(), 3);
/// assert_eq!(slice.as_mut_ptr(), NonNull::<i8>::dangling().as_ptr());
/// ```
#[inline]
#[must_use]
#[unstable(feature = "slice_ptr_get", issue = "74265")]
#[rustc_const_unstable(feature = "slice_ptr_get", issue = "74265")]
pub const fn as_mut_ptr(self) -> *mut T {
self.as_non_null_ptr().as_ptr()
}
/// 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`].
///
/// [`as_ref`]: NonNull::as_ref
/// [`as_uninit_slice_mut`]: NonNull::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, 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!
///
/// See also [`slice::from_raw_parts`].
///
/// [valid]: crate::ptr#safety
#[inline]
#[must_use]
#[unstable(feature = "ptr_as_uninit", issue = "75402")]
#[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
pub const unsafe fn as_uninit_slice<'a>(self) -> &'a [MaybeUninit<T>] {
// SAFETY: the caller must uphold the safety contract for `as_uninit_slice`.
unsafe { slice::from_raw_parts(self.cast().as_ptr(), self.len()) }
}
/// 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`].
///
/// [`as_mut`]: NonNull::as_mut
/// [`as_uninit_slice`]: NonNull::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, while this reference exists, 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`].
///
/// [valid]: crate::ptr#safety
///
/// # Examples
///
/// ```rust
/// #![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.
/// # #[allow(unused_variables)]
/// let slice: &mut [MaybeUninit<u8>] = unsafe { memory.as_uninit_slice_mut() };
/// # Ok::<_, std::alloc::AllocError>(())
/// ```
#[inline]
#[must_use]
#[unstable(feature = "ptr_as_uninit", issue = "75402")]
#[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
pub const unsafe fn as_uninit_slice_mut<'a>(self) -> &'a mut [MaybeUninit<T>] {
// SAFETY: the caller must uphold the safety contract for `as_uninit_slice_mut`.
unsafe { slice::from_raw_parts_mut(self.cast().as_ptr(), self.len()) }
}
/// 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 dereferenceable
/// is *[undefined behavior]* even if the resulting pointer is not used.
///
/// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
///
/// # Examples
///
/// ```
/// #![feature(slice_ptr_get)]
/// 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));
/// }
/// ```
#[unstable(feature = "slice_ptr_get", issue = "74265")]
#[inline]
pub unsafe fn get_unchecked_mut<I>(self, index: I) -> NonNull<I::Output>
where
I: SliceIndex<[T]>,
{
// SAFETY: the caller ensures that `self` is dereferenceable and `index` in-bounds.
// As a consequence, the resulting pointer cannot be null.
unsafe { NonNull::new_unchecked(self.as_ptr().get_unchecked_mut(index)) }
}
}
#[stable(feature = "nonnull", since = "1.25.0")]
impl<T: ?Sized> Clone for NonNull<T> {
#[inline(always)]
fn clone(&self) -> Self {
*self
}
}
#[stable(feature = "nonnull", since = "1.25.0")]
impl<T: ?Sized> Copy for NonNull<T> {}
#[unstable(feature = "coerce_unsized", issue = "18598")]
impl<T: ?Sized, U: ?Sized> CoerceUnsized<NonNull<U>> for NonNull<T> where T: Unsize<U> {}
#[unstable(feature = "dispatch_from_dyn", issue = "none")]
impl<T: ?Sized, U: ?Sized> DispatchFromDyn<NonNull<U>> for NonNull<T> where T: Unsize<U> {}
#[stable(feature = "nonnull", since = "1.25.0")]
impl<T: ?Sized> fmt::Debug for NonNull<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Pointer::fmt(&self.as_ptr(), f)
}
}
#[stable(feature = "nonnull", since = "1.25.0")]
impl<T: ?Sized> fmt::Pointer for NonNull<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Pointer::fmt(&self.as_ptr(), f)
}
}
#[stable(feature = "nonnull", since = "1.25.0")]
impl<T: ?Sized> Eq for NonNull<T> {}
#[stable(feature = "nonnull", since = "1.25.0")]
impl<T: ?Sized> PartialEq for NonNull<T> {
#[inline]
fn eq(&self, other: &Self) -> bool {
self.as_ptr() == other.as_ptr()
}
}
#[stable(feature = "nonnull", since = "1.25.0")]
impl<T: ?Sized> Ord for NonNull<T> {
#[inline]
fn cmp(&self, other: &Self) -> Ordering {
self.as_ptr().cmp(&other.as_ptr())
}
}
#[stable(feature = "nonnull", since = "1.25.0")]
impl<T: ?Sized> PartialOrd for NonNull<T> {
#[inline]
fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
self.as_ptr().partial_cmp(&other.as_ptr())
}
}
#[stable(feature = "nonnull", since = "1.25.0")]
impl<T: ?Sized> hash::Hash for NonNull<T> {
#[inline]
fn hash<H: hash::Hasher>(&self, state: &mut H) {
self.as_ptr().hash(state)
}
}
#[unstable(feature = "ptr_internals", issue = "none")]
impl<T: ?Sized> From<Unique<T>> for NonNull<T> {
#[inline]
fn from(unique: Unique<T>) -> Self {
// SAFETY: A Unique pointer cannot be null, so the conditions for
// new_unchecked() are respected.
unsafe { NonNull::new_unchecked(unique.as_ptr()) }
}
}
#[stable(feature = "nonnull", since = "1.25.0")]
impl<T: ?Sized> From<&mut T> for NonNull<T> {
/// Converts a `&mut T` to a `NonNull<T>`.
///
/// This conversion is safe and infallible since references cannot be null.
#[inline]
fn from(reference: &mut T) -> Self {
// SAFETY: A mutable reference cannot be null.
unsafe { NonNull { pointer: reference as *mut T } }
}
}
#[stable(feature = "nonnull", since = "1.25.0")]
impl<T: ?Sized> From<&T> for NonNull<T> {
/// Converts a `&T` to a `NonNull<T>`.
///
/// This conversion is safe and infallible since references cannot be null.
#[inline]
fn from(reference: &T) -> Self {
// SAFETY: A reference cannot be null, so the conditions for
// new_unchecked() are respected.
unsafe { NonNull { pointer: reference as *const T } }
}
}
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