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nest-open-source / manifest_repos / toolchain / 6143c57c644e0da7c4a10d1b4af322f92e74e6f7 / . / x86_64 / usr / lib / rustlib / src / rust / library / core / src / ptr / mut_ptr.rs
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use super::*;
use crate::cmp::Ordering::{self, Equal, Greater, Less};
use crate::intrinsics;
use crate::slice::{self, SliceIndex};
impl<T: ?Sized> *mut T {
/// Returns `true` if the pointer is null.
///
/// Note that unsized types have many possible null pointers, as only the
/// raw data pointer is considered, not their length, vtable, etc.
/// Therefore, two pointers that are null may still not compare equal to
/// each other.
///
/// ## Behavior during const evaluation
///
/// When this function is used during const evaluation, it may return `false` for pointers
/// that turn out to be null at runtime. Specifically, when a pointer to some memory
/// is offset beyond its bounds in such a way that the resulting pointer is null,
/// the function will still return `false`. There is no way for CTFE to know
/// the absolute position of that memory, so we cannot tell if the pointer is
/// null or not.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let mut s = [1, 2, 3];
/// let ptr: *mut u32 = s.as_mut_ptr();
/// assert!(!ptr.is_null());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_ptr_is_null", issue = "74939")]
#[inline]
pub const fn is_null(self) -> bool {
// Compare via a cast to a thin pointer, so fat pointers are only
// considering their "data" part for null-ness.
match (self as *mut u8).guaranteed_eq(null_mut()) {
None => false,
Some(res) => res,
}
}
/// Casts to a pointer of another type.
#[stable(feature = "ptr_cast", since = "1.38.0")]
#[rustc_const_stable(feature = "const_ptr_cast", since = "1.38.0")]
#[inline(always)]
pub const fn cast<U>(self) -> *mut U {
self as _
}
/// Use the pointer value in a new pointer of another type.
///
/// In case `val` is a (fat) pointer to an unsized type, this operation
/// will ignore the pointer part, whereas for (thin) pointers to sized
/// types, this has the same effect as a simple cast.
///
/// The resulting pointer will have provenance of `self`, i.e., for a fat
/// pointer, this operation is semantically the same as creating a new
/// fat pointer with the data pointer value of `self` but the metadata of
/// `val`.
///
/// # Examples
///
/// This function is primarily useful for allowing byte-wise pointer
/// arithmetic on potentially fat pointers:
///
/// ```
/// #![feature(set_ptr_value)]
/// # use core::fmt::Debug;
/// let mut arr: [i32; 3] = [1, 2, 3];
/// let mut ptr = arr.as_mut_ptr() as *mut dyn Debug;
/// let thin = ptr as *mut u8;
/// unsafe {
/// ptr = thin.add(8).with_metadata_of(ptr);
/// # assert_eq!(*(ptr as *mut i32), 3);
/// println!("{:?}", &*ptr); // will print "3"
/// }
/// ```
#[unstable(feature = "set_ptr_value", issue = "75091")]
#[rustc_const_unstable(feature = "set_ptr_value", issue = "75091")]
#[must_use = "returns a new pointer rather than modifying its argument"]
#[inline]
pub const fn with_metadata_of<U>(self, meta: *const U) -> *mut U
where
U: ?Sized,
{
from_raw_parts_mut::<U>(self as *mut (), metadata(meta))
}
/// Changes constness without changing the type.
///
/// This is a bit safer than `as` because it wouldn't silently change the type if the code is
/// refactored.
///
/// While not strictly required (`*mut T` coerces to `*const T`), this is provided for symmetry
/// with [`cast_mut`] on `*const T` and may have documentation value if used instead of implicit
/// coercion.
///
/// [`cast_mut`]: #method.cast_mut
#[stable(feature = "ptr_const_cast", since = "1.65.0")]
#[rustc_const_stable(feature = "ptr_const_cast", since = "1.65.0")]
#[inline(always)]
pub const fn cast_const(self) -> *const T {
self as _
}
/// Casts a pointer to its raw bits.
///
/// This is equivalent to `as usize`, but is more specific to enhance readability.
/// The inverse method is [`from_bits`](#method.from_bits-1).
///
/// In particular, `*p as usize` and `p as usize` will both compile for
/// pointers to numeric types but do very different things, so using this
/// helps emphasize that reading the bits was intentional.
///
/// # Examples
///
/// ```
/// #![feature(ptr_to_from_bits)]
/// # #[cfg(not(miri))] { // doctest does not work with strict provenance
/// let mut array = [13, 42];
/// let mut it = array.iter_mut();
/// let p0: *mut i32 = it.next().unwrap();
/// assert_eq!(<*mut _>::from_bits(p0.to_bits()), p0);
/// let p1: *mut i32 = it.next().unwrap();
/// assert_eq!(p1.to_bits() - p0.to_bits(), 4);
/// }
/// ```
#[unstable(feature = "ptr_to_from_bits", issue = "91126")]
#[deprecated(
since = "1.67",
note = "replaced by the `exposed_addr` method, or update your code \
to follow the strict provenance rules using its APIs"
)]
#[inline(always)]
pub fn to_bits(self) -> usize
where
T: Sized,
{
self as usize
}
/// Creates a pointer from its raw bits.
///
/// This is equivalent to `as *mut T`, but is more specific to enhance readability.
/// The inverse method is [`to_bits`](#method.to_bits-1).
///
/// # Examples
///
/// ```
/// #![feature(ptr_to_from_bits)]
/// # #[cfg(not(miri))] { // doctest does not work with strict provenance
/// use std::ptr::NonNull;
/// let dangling: *mut u8 = NonNull::dangling().as_ptr();
/// assert_eq!(<*mut u8>::from_bits(1), dangling);
/// }
/// ```
#[unstable(feature = "ptr_to_from_bits", issue = "91126")]
#[deprecated(
since = "1.67",
note = "replaced by the `ptr::from_exposed_addr_mut` function, or \
update your code to follow the strict provenance rules using its APIs"
)]
#[allow(fuzzy_provenance_casts)] // this is an unstable and semi-deprecated cast function
#[inline(always)]
pub fn from_bits(bits: usize) -> Self
where
T: Sized,
{
bits as Self
}
/// Gets the "address" portion of the pointer.
///
/// This is similar to `self as usize`, which semantically discards *provenance* and
/// *address-space* information. However, unlike `self as usize`, casting the returned address
/// back to a pointer yields [`invalid`][], which is undefined behavior to dereference. To
/// properly restore the lost information and obtain a dereferenceable pointer, use
/// [`with_addr`][pointer::with_addr] or [`map_addr`][pointer::map_addr].
///
/// If using those APIs is not possible because there is no way to preserve a pointer with the
/// required provenance, use [`expose_addr`][pointer::expose_addr] and
/// [`from_exposed_addr_mut`][from_exposed_addr_mut] instead. However, note that this makes
/// your code less portable and less amenable to tools that check for compliance with the Rust
/// memory model.
///
/// On most platforms this will produce a value with the same bytes as the original
/// pointer, because all the bytes are dedicated to describing the address.
/// Platforms which need to store additional information in the pointer may
/// perform a change of representation to produce a value containing only the address
/// portion of the pointer. What that means is up to the platform to define.
///
/// This API and its claimed semantics are part of the Strict Provenance experiment, and as such
/// might change in the future (including possibly weakening this so it becomes wholly
/// equivalent to `self as usize`). See the [module documentation][crate::ptr] for details.
#[must_use]
#[inline(always)]
#[unstable(feature = "strict_provenance", issue = "95228")]
pub fn addr(self) -> usize
where
T: Sized,
{
// FIXME(strict_provenance_magic): I am magic and should be a compiler intrinsic.
// SAFETY: Pointer-to-integer transmutes are valid (if you are okay with losing the
// provenance).
unsafe { mem::transmute(self) }
}
/// Gets the "address" portion of the pointer, and 'exposes' the "provenance" part for future
/// use in [`from_exposed_addr`][].
///
/// This is equivalent to `self as usize`, which semantically discards *provenance* and
/// *address-space* information. Furthermore, this (like the `as` cast) has the implicit
/// side-effect of marking the provenance as 'exposed', so on platforms that support it you can
/// later call [`from_exposed_addr_mut`][] to reconstitute the original pointer including its
/// provenance. (Reconstructing address space information, if required, is your responsibility.)
///
/// Using this method means that code is *not* following Strict Provenance rules. Supporting
/// [`from_exposed_addr_mut`][] complicates specification and reasoning and may not be supported
/// by tools that help you to stay conformant with the Rust memory model, so it is recommended
/// to use [`addr`][pointer::addr] wherever possible.
///
/// On most platforms this will produce a value with the same bytes as the original pointer,
/// because all the bytes are dedicated to describing the address. Platforms which need to store
/// additional information in the pointer may not support this operation, since the 'expose'
/// side-effect which is required for [`from_exposed_addr_mut`][] to work is typically not
/// available.
///
/// This API and its claimed semantics are part of the Strict Provenance experiment, see the
/// [module documentation][crate::ptr] for details.
///
/// [`from_exposed_addr_mut`]: from_exposed_addr_mut
#[must_use]
#[inline(always)]
#[unstable(feature = "strict_provenance", issue = "95228")]
pub fn expose_addr(self) -> usize
where
T: Sized,
{
// FIXME(strict_provenance_magic): I am magic and should be a compiler intrinsic.
self as usize
}
/// Creates a new pointer with the given address.
///
/// This performs the same operation as an `addr as ptr` cast, but copies
/// the *address-space* and *provenance* of `self` to the new pointer.
/// This allows us to dynamically preserve and propagate this important
/// information in a way that is otherwise impossible with a unary cast.
///
/// This is equivalent to using [`wrapping_offset`][pointer::wrapping_offset] to offset
/// `self` to the given address, and therefore has all the same capabilities and restrictions.
///
/// This API and its claimed semantics are part of the Strict Provenance experiment,
/// see the [module documentation][crate::ptr] for details.
#[must_use]
#[inline]
#[unstable(feature = "strict_provenance", issue = "95228")]
pub fn with_addr(self, addr: usize) -> Self
where
T: Sized,
{
// FIXME(strict_provenance_magic): I am magic and should be a compiler intrinsic.
//
// In the mean-time, this operation is defined to be "as if" it was
// a wrapping_offset, so we can emulate it as such. This should properly
// restore pointer provenance even under today's compiler.
let self_addr = self.addr() as isize;
let dest_addr = addr as isize;
let offset = dest_addr.wrapping_sub(self_addr);
// This is the canonical desugarring of this operation
self.wrapping_byte_offset(offset)
}
/// Creates a new pointer by mapping `self`'s address to a new one.
///
/// This is a convenience for [`with_addr`][pointer::with_addr], see that method for details.
///
/// This API and its claimed semantics are part of the Strict Provenance experiment,
/// see the [module documentation][crate::ptr] for details.
#[must_use]
#[inline]
#[unstable(feature = "strict_provenance", issue = "95228")]
pub fn map_addr(self, f: impl FnOnce(usize) -> usize) -> Self
where
T: Sized,
{
self.with_addr(f(self.addr()))
}
/// Decompose a (possibly wide) pointer into its address and metadata components.
///
/// The pointer can be later reconstructed with [`from_raw_parts_mut`].
#[unstable(feature = "ptr_metadata", issue = "81513")]
#[rustc_const_unstable(feature = "ptr_metadata", issue = "81513")]
#[inline]
pub const fn to_raw_parts(self) -> (*mut (), <T as super::Pointee>::Metadata) {
(self.cast(), super::metadata(self))
}
/// Returns `None` if the pointer is null, or else returns a shared reference to
/// the value wrapped in `Some`. If the value may be uninitialized, [`as_uninit_ref`]
/// must be used instead.
///
/// For the mutable counterpart see [`as_mut`].
///
/// [`as_uninit_ref`]: #method.as_uninit_ref-1
/// [`as_mut`]: #method.as_mut
///
/// # Safety
///
/// When calling this method, you have to ensure that *either* the pointer is null *or*
/// 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.)
///
/// [the module documentation]: crate::ptr#safety
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let ptr: *mut u8 = &mut 10u8 as *mut u8;
///
/// unsafe {
/// if let Some(val_back) = ptr.as_ref() {
/// println!("We got back the value: {val_back}!");
/// }
/// }
/// ```
///
/// # Null-unchecked version
///
/// If you are sure the pointer can never be null and are looking for some kind of
/// `as_ref_unchecked` that returns the `&T` instead of `Option<&T>`, know that you can
/// dereference the pointer directly.
///
/// ```
/// let ptr: *mut u8 = &mut 10u8 as *mut u8;
///
/// unsafe {
/// let val_back = &*ptr;
/// println!("We got back the value: {val_back}!");
/// }
/// ```
#[stable(feature = "ptr_as_ref", since = "1.9.0")]
#[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
#[inline]
pub const unsafe fn as_ref<'a>(self) -> Option<&'a T> {
// SAFETY: the caller must guarantee that `self` is valid for a
// reference if it isn't null.
if self.is_null() { None } else { unsafe { Some(&*self) } }
}
/// Returns `None` if the pointer is null, or else returns a shared reference to
/// the value wrapped in `Some`. 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`]: #method.as_ref-1
/// [`as_uninit_mut`]: #method.as_uninit_mut
///
/// # Safety
///
/// When calling this method, you have to ensure that *either* the pointer is null *or*
/// 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
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(ptr_as_uninit)]
///
/// let ptr: *mut u8 = &mut 10u8 as *mut u8;
///
/// unsafe {
/// if let Some(val_back) = ptr.as_uninit_ref() {
/// println!("We got back the value: {}!", val_back.assume_init());
/// }
/// }
/// ```
#[inline]
#[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) -> Option<&'a MaybeUninit<T>>
where
T: Sized,
{
// SAFETY: the caller must guarantee that `self` meets all the
// requirements for a reference.
if self.is_null() { None } else { Some(unsafe { &*(self as *const MaybeUninit<T>) }) }
}
/// Calculates the offset from a pointer.
///
/// `count` is in units of T; e.g., a `count` of 3 represents a pointer
/// offset of `3 * size_of::<T>()` bytes.
///
/// # Safety
///
/// If any of the following conditions are violated, the result is Undefined
/// Behavior:
///
/// * Both the starting and resulting pointer must be either in bounds or one
/// byte past the end of the same [allocated object].
///
/// * The computed offset, **in bytes**, cannot overflow an `isize`.
///
/// * The offset being in bounds cannot rely on "wrapping around" the address
/// space. That is, the infinite-precision sum, **in bytes** must fit in a usize.
///
/// The compiler and standard library generally tries to ensure allocations
/// never reach a size where an offset is a concern. For instance, `Vec`
/// and `Box` ensure they never allocate more than `isize::MAX` bytes, so
/// `vec.as_ptr().add(vec.len())` is always safe.
///
/// Most platforms fundamentally can't even construct such an allocation.
/// For instance, no known 64-bit platform can ever serve a request
/// for 2<sup>63</sup> bytes due to page-table limitations or splitting the address space.
/// However, some 32-bit and 16-bit platforms may successfully serve a request for
/// more than `isize::MAX` bytes with things like Physical Address
/// Extension. As such, memory acquired directly from allocators or memory
/// mapped files *may* be too large to handle with this function.
///
/// Consider using [`wrapping_offset`] instead if these constraints are
/// difficult to satisfy. The only advantage of this method is that it
/// enables more aggressive compiler optimizations.
///
/// [`wrapping_offset`]: #method.wrapping_offset
/// [allocated object]: crate::ptr#allocated-object
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let mut s = [1, 2, 3];
/// let ptr: *mut u32 = s.as_mut_ptr();
///
/// unsafe {
/// println!("{}", *ptr.offset(1));
/// println!("{}", *ptr.offset(2));
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[must_use = "returns a new pointer rather than modifying its argument"]
#[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn offset(self, count: isize) -> *mut T
where
T: Sized,
{
// SAFETY: the caller must uphold the safety contract for `offset`.
// The obtained pointer is valid for writes since the caller must
// guarantee that it points to the same allocated object as `self`.
unsafe { intrinsics::offset(self, count) as *mut T }
}
/// Calculates the offset from a pointer in bytes.
///
/// `count` is in units of **bytes**.
///
/// This is purely a convenience for casting to a `u8` pointer and
/// using [offset][pointer::offset] on it. See that method for documentation
/// and safety requirements.
///
/// For non-`Sized` pointees this operation changes only the data pointer,
/// leaving the metadata untouched.
#[must_use]
#[inline(always)]
#[unstable(feature = "pointer_byte_offsets", issue = "96283")]
#[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn byte_offset(self, count: isize) -> Self {
// SAFETY: the caller must uphold the safety contract for `offset`.
unsafe { self.cast::<u8>().offset(count).with_metadata_of(self) }
}
/// Calculates the offset from a pointer using wrapping arithmetic.
/// `count` is in units of T; e.g., a `count` of 3 represents a pointer
/// offset of `3 * size_of::<T>()` bytes.
///
/// # Safety
///
/// This operation itself is always safe, but using the resulting pointer is not.
///
/// The resulting pointer "remembers" the [allocated object] that `self` points to; it must not
/// be used to read or write other allocated objects.
///
/// In other words, `let z = x.wrapping_offset((y as isize) - (x as isize))` does *not* make `z`
/// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
/// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless
/// `x` and `y` point into the same allocated object.
///
/// Compared to [`offset`], this method basically delays the requirement of staying within the
/// same allocated object: [`offset`] is immediate Undefined Behavior when crossing object
/// boundaries; `wrapping_offset` produces a pointer but still leads to Undefined Behavior if a
/// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`offset`]
/// can be optimized better and is thus preferable in performance-sensitive code.
///
/// The delayed check only considers the value of the pointer that was dereferenced, not the
/// intermediate values used during the computation of the final result. For example,
/// `x.wrapping_offset(o).wrapping_offset(o.wrapping_neg())` is always the same as `x`. In other
/// words, leaving the allocated object and then re-entering it later is permitted.
///
/// [`offset`]: #method.offset
/// [allocated object]: crate::ptr#allocated-object
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// // Iterate using a raw pointer in increments of two elements
/// let mut data = [1u8, 2, 3, 4, 5];
/// let mut ptr: *mut u8 = data.as_mut_ptr();
/// let step = 2;
/// let end_rounded_up = ptr.wrapping_offset(6);
///
/// while ptr != end_rounded_up {
/// unsafe {
/// *ptr = 0;
/// }
/// ptr = ptr.wrapping_offset(step);
/// }
/// assert_eq!(&data, &[0, 2, 0, 4, 0]);
/// ```
#[stable(feature = "ptr_wrapping_offset", since = "1.16.0")]
#[must_use = "returns a new pointer rather than modifying its argument"]
#[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
#[inline(always)]
pub const fn wrapping_offset(self, count: isize) -> *mut T
where
T: Sized,
{
// SAFETY: the `arith_offset` intrinsic has no prerequisites to be called.
unsafe { intrinsics::arith_offset(self, count) as *mut T }
}
/// Calculates the offset from a pointer in bytes using wrapping arithmetic.
///
/// `count` is in units of **bytes**.
///
/// This is purely a convenience for casting to a `u8` pointer and
/// using [wrapping_offset][pointer::wrapping_offset] on it. See that method
/// for documentation.
///
/// For non-`Sized` pointees this operation changes only the data pointer,
/// leaving the metadata untouched.
#[must_use]
#[inline(always)]
#[unstable(feature = "pointer_byte_offsets", issue = "96283")]
#[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
pub const fn wrapping_byte_offset(self, count: isize) -> Self {
self.cast::<u8>().wrapping_offset(count).with_metadata_of(self)
}
/// Masks out bits of the pointer according to a mask.
///
/// This is convenience for `ptr.map_addr(|a| a & mask)`.
///
/// For non-`Sized` pointees this operation changes only the data pointer,
/// leaving the metadata untouched.
///
/// ## Examples
///
/// ```
/// #![feature(ptr_mask, strict_provenance)]
/// let mut v = 17_u32;
/// let ptr: *mut u32 = &mut v;
///
/// // `u32` is 4 bytes aligned,
/// // which means that lower 2 bits are always 0.
/// let tag_mask = 0b11;
/// let ptr_mask = !tag_mask;
///
/// // We can store something in these lower bits
/// let tagged_ptr = ptr.map_addr(|a| a | 0b10);
///
/// // Get the "tag" back
/// let tag = tagged_ptr.addr() & tag_mask;
/// assert_eq!(tag, 0b10);
///
/// // Note that `tagged_ptr` is unaligned, it's UB to read from/write to it.
/// // To get original pointer `mask` can be used:
/// let masked_ptr = tagged_ptr.mask(ptr_mask);
/// assert_eq!(unsafe { *masked_ptr }, 17);
///
/// unsafe { *masked_ptr = 0 };
/// assert_eq!(v, 0);
/// ```
#[unstable(feature = "ptr_mask", issue = "98290")]
#[must_use = "returns a new pointer rather than modifying its argument"]
#[inline(always)]
pub fn mask(self, mask: usize) -> *mut T {
intrinsics::ptr_mask(self.cast::<()>(), mask).cast_mut().with_metadata_of(self)
}
/// Returns `None` if the pointer is null, or else returns a unique reference to
/// the value wrapped in `Some`. If the value may be uninitialized, [`as_uninit_mut`]
/// must be used instead.
///
/// For the shared counterpart see [`as_ref`].
///
/// [`as_uninit_mut`]: #method.as_uninit_mut
/// [`as_ref`]: #method.as_ref-1
///
/// # Safety
///
/// When calling this method, you have to ensure that *either* the pointer is null *or*
/// 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.)
///
/// [the module documentation]: crate::ptr#safety
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let mut s = [1, 2, 3];
/// let ptr: *mut u32 = s.as_mut_ptr();
/// let first_value = unsafe { ptr.as_mut().unwrap() };
/// *first_value = 4;
/// # assert_eq!(s, [4, 2, 3]);
/// println!("{s:?}"); // It'll print: "[4, 2, 3]".
/// ```
///
/// # Null-unchecked version
///
/// If you are sure the pointer can never be null and are looking for some kind of
/// `as_mut_unchecked` that returns the `&mut T` instead of `Option<&mut T>`, know that
/// you can dereference the pointer directly.
///
/// ```
/// let mut s = [1, 2, 3];
/// let ptr: *mut u32 = s.as_mut_ptr();
/// let first_value = unsafe { &mut *ptr };
/// *first_value = 4;
/// # assert_eq!(s, [4, 2, 3]);
/// println!("{s:?}"); // It'll print: "[4, 2, 3]".
/// ```
#[stable(feature = "ptr_as_ref", since = "1.9.0")]
#[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
#[inline]
pub const unsafe fn as_mut<'a>(self) -> Option<&'a mut T> {
// SAFETY: the caller must guarantee that `self` is be valid for
// a mutable reference if it isn't null.
if self.is_null() { None } else { unsafe { Some(&mut *self) } }
}
/// Returns `None` if the pointer is null, or else returns a unique reference to
/// the value wrapped in `Some`. 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`]: #method.as_mut
/// [`as_uninit_ref`]: #method.as_uninit_ref-1
///
/// # Safety
///
/// When calling this method, you have to ensure that *either* the pointer is null *or*
/// 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]
#[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) -> Option<&'a mut MaybeUninit<T>>
where
T: Sized,
{
// SAFETY: the caller must guarantee that `self` meets all the
// requirements for a reference.
if self.is_null() { None } else { Some(unsafe { &mut *(self as *mut MaybeUninit<T>) }) }
}
/// Returns whether two pointers are guaranteed to be equal.
///
/// At runtime this function behaves like `Some(self == other)`.
/// However, in some contexts (e.g., compile-time evaluation),
/// it is not always possible to determine equality of two pointers, so this function may
/// spuriously return `None` for pointers that later actually turn out to have its equality known.
/// But when it returns `Some`, the pointers' equality is guaranteed to be known.
///
/// The return value may change from `Some` to `None` and vice versa depending on the compiler
/// version and unsafe code must not
/// rely on the result of this function for soundness. It is suggested to only use this function
/// for performance optimizations where spurious `None` return values by this function do not
/// affect the outcome, but just the performance.
/// The consequences of using this method to make runtime and compile-time code behave
/// differently have not been explored. This method should not be used to introduce such
/// differences, and it should also not be stabilized before we have a better understanding
/// of this issue.
#[unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
#[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
#[inline]
pub const fn guaranteed_eq(self, other: *mut T) -> Option<bool>
where
T: Sized,
{
(self as *const T).guaranteed_eq(other as _)
}
/// Returns whether two pointers are guaranteed to be inequal.
///
/// At runtime this function behaves like `Some(self != other)`.
/// However, in some contexts (e.g., compile-time evaluation),
/// it is not always possible to determine inequality of two pointers, so this function may
/// spuriously return `None` for pointers that later actually turn out to have its inequality known.
/// But when it returns `Some`, the pointers' inequality is guaranteed to be known.
///
/// The return value may change from `Some` to `None` and vice versa depending on the compiler
/// version and unsafe code must not
/// rely on the result of this function for soundness. It is suggested to only use this function
/// for performance optimizations where spurious `None` return values by this function do not
/// affect the outcome, but just the performance.
/// The consequences of using this method to make runtime and compile-time code behave
/// differently have not been explored. This method should not be used to introduce such
/// differences, and it should also not be stabilized before we have a better understanding
/// of this issue.
#[unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
#[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
#[inline]
pub const fn guaranteed_ne(self, other: *mut T) -> Option<bool>
where
T: Sized,
{
(self as *const T).guaranteed_ne(other as _)
}
/// Calculates the distance between two pointers. The returned value is in
/// units of T: the distance in bytes divided by `mem::size_of::<T>()`.
///
/// This function is the inverse of [`offset`].
///
/// [`offset`]: #method.offset-1
///
/// # Safety
///
/// If any of the following conditions are violated, the result is Undefined
/// Behavior:
///
/// * Both the starting and other pointer must be either in bounds or one
/// byte past the end of the same [allocated object].
///
/// * Both pointers must be *derived from* a pointer to the same object.
/// (See below for an example.)
///
/// * The distance between the pointers, in bytes, must be an exact multiple
/// of the size of `T`.
///
/// * The distance between the pointers, **in bytes**, cannot overflow an `isize`.
///
/// * The distance being in bounds cannot rely on "wrapping around" the address space.
///
/// Rust types are never larger than `isize::MAX` and Rust allocations never wrap around the
/// address space, so two pointers within some value of any Rust type `T` will always satisfy
/// the last two conditions. The standard library also generally ensures that allocations
/// never reach a size where an offset is a concern. For instance, `Vec` and `Box` ensure they
/// never allocate more than `isize::MAX` bytes, so `ptr_into_vec.offset_from(vec.as_ptr())`
/// always satisfies the last two conditions.
///
/// Most platforms fundamentally can't even construct such a large allocation.
/// For instance, no known 64-bit platform can ever serve a request
/// for 2<sup>63</sup> bytes due to page-table limitations or splitting the address space.
/// However, some 32-bit and 16-bit platforms may successfully serve a request for
/// more than `isize::MAX` bytes with things like Physical Address
/// Extension. As such, memory acquired directly from allocators or memory
/// mapped files *may* be too large to handle with this function.
/// (Note that [`offset`] and [`add`] also have a similar limitation and hence cannot be used on
/// such large allocations either.)
///
/// [`add`]: #method.add
/// [allocated object]: crate::ptr#allocated-object
///
/// # Panics
///
/// This function panics if `T` is a Zero-Sized Type ("ZST").
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let mut a = [0; 5];
/// let ptr1: *mut i32 = &mut a[1];
/// let ptr2: *mut i32 = &mut a[3];
/// unsafe {
/// assert_eq!(ptr2.offset_from(ptr1), 2);
/// assert_eq!(ptr1.offset_from(ptr2), -2);
/// assert_eq!(ptr1.offset(2), ptr2);
/// assert_eq!(ptr2.offset(-2), ptr1);
/// }
/// ```
///
/// *Incorrect* usage:
///
/// ```rust,no_run
/// let ptr1 = Box::into_raw(Box::new(0u8));
/// let ptr2 = Box::into_raw(Box::new(1u8));
/// let diff = (ptr2 as isize).wrapping_sub(ptr1 as isize);
/// // Make ptr2_other an "alias" of ptr2, but derived from ptr1.
/// let ptr2_other = (ptr1 as *mut u8).wrapping_offset(diff);
/// assert_eq!(ptr2 as usize, ptr2_other as usize);
/// // Since ptr2_other and ptr2 are derived from pointers to different objects,
/// // computing their offset is undefined behavior, even though
/// // they point to the same address!
/// unsafe {
/// let zero = ptr2_other.offset_from(ptr2); // Undefined Behavior
/// }
/// ```
#[stable(feature = "ptr_offset_from", since = "1.47.0")]
#[rustc_const_stable(feature = "const_ptr_offset_from", since = "1.65.0")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn offset_from(self, origin: *const T) -> isize
where
T: Sized,
{
// SAFETY: the caller must uphold the safety contract for `offset_from`.
unsafe { (self as *const T).offset_from(origin) }
}
/// Calculates the distance between two pointers. The returned value is in
/// units of **bytes**.
///
/// This is purely a convenience for casting to a `u8` pointer and
/// using [offset_from][pointer::offset_from] on it. See that method for
/// documentation and safety requirements.
///
/// For non-`Sized` pointees this operation considers only the data pointers,
/// ignoring the metadata.
#[inline(always)]
#[unstable(feature = "pointer_byte_offsets", issue = "96283")]
#[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn byte_offset_from<U: ?Sized>(self, origin: *const U) -> isize {
// SAFETY: the caller must uphold the safety contract for `offset_from`.
unsafe { self.cast::<u8>().offset_from(origin.cast::<u8>()) }
}
/// Calculates the distance between two pointers, *where it's known that
/// `self` is equal to or greater than `origin`*. The returned value is in
/// units of T: the distance in bytes is divided by `mem::size_of::<T>()`.
///
/// This computes the same value that [`offset_from`](#method.offset_from)
/// would compute, but with the added precondition that the offset is
/// guaranteed to be non-negative. This method is equivalent to
/// `usize::from(self.offset_from(origin)).unwrap_unchecked()`,
/// but it provides slightly more information to the optimizer, which can
/// sometimes allow it to optimize slightly better with some backends.
///
/// This method can be though of as recovering the `count` that was passed
/// to [`add`](#method.add) (or, with the parameters in the other order,
/// to [`sub`](#method.sub)). The following are all equivalent, assuming
/// that their safety preconditions are met:
/// ```rust
/// # #![feature(ptr_sub_ptr)]
/// # unsafe fn blah(ptr: *mut i32, origin: *mut i32, count: usize) -> bool {
/// ptr.sub_ptr(origin) == count
/// # &&
/// origin.add(count) == ptr
/// # &&
/// ptr.sub(count) == origin
/// # }
/// ```
///
/// # Safety
///
/// - The distance between the pointers must be non-negative (`self >= origin`)
///
/// - *All* the safety conditions of [`offset_from`](#method.offset_from)
/// apply to this method as well; see it for the full details.
///
/// Importantly, despite the return type of this method being able to represent
/// a larger offset, it's still *not permitted* to pass pointers which differ
/// by more than `isize::MAX` *bytes*. As such, the result of this method will
/// always be less than or equal to `isize::MAX as usize`.
///
/// # Panics
///
/// This function panics if `T` is a Zero-Sized Type ("ZST").
///
/// # Examples
///
/// ```
/// #![feature(ptr_sub_ptr)]
///
/// let mut a = [0; 5];
/// let p: *mut i32 = a.as_mut_ptr();
/// unsafe {
/// let ptr1: *mut i32 = p.add(1);
/// let ptr2: *mut i32 = p.add(3);
///
/// assert_eq!(ptr2.sub_ptr(ptr1), 2);
/// assert_eq!(ptr1.add(2), ptr2);
/// assert_eq!(ptr2.sub(2), ptr1);
/// assert_eq!(ptr2.sub_ptr(ptr2), 0);
/// }
///
/// // This would be incorrect, as the pointers are not correctly ordered:
/// // ptr1.offset_from(ptr2)
#[unstable(feature = "ptr_sub_ptr", issue = "95892")]
#[rustc_const_unstable(feature = "const_ptr_sub_ptr", issue = "95892")]
#[inline]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn sub_ptr(self, origin: *const T) -> usize
where
T: Sized,
{
// SAFETY: the caller must uphold the safety contract for `sub_ptr`.
unsafe { (self as *const T).sub_ptr(origin) }
}
/// Calculates the offset from a pointer (convenience for `.offset(count as isize)`).
///
/// `count` is in units of T; e.g., a `count` of 3 represents a pointer
/// offset of `3 * size_of::<T>()` bytes.
///
/// # Safety
///
/// If any of the following conditions are violated, the result is Undefined
/// Behavior:
///
/// * Both the starting and resulting pointer must be either in bounds or one
/// byte past the end of the same [allocated object].
///
/// * The computed offset, **in bytes**, cannot overflow an `isize`.
///
/// * The offset being in bounds cannot rely on "wrapping around" the address
/// space. That is, the infinite-precision sum must fit in a `usize`.
///
/// The compiler and standard library generally tries to ensure allocations
/// never reach a size where an offset is a concern. For instance, `Vec`
/// and `Box` ensure they never allocate more than `isize::MAX` bytes, so
/// `vec.as_ptr().add(vec.len())` is always safe.
///
/// Most platforms fundamentally can't even construct such an allocation.
/// For instance, no known 64-bit platform can ever serve a request
/// for 2<sup>63</sup> bytes due to page-table limitations or splitting the address space.
/// However, some 32-bit and 16-bit platforms may successfully serve a request for
/// more than `isize::MAX` bytes with things like Physical Address
/// Extension. As such, memory acquired directly from allocators or memory
/// mapped files *may* be too large to handle with this function.
///
/// Consider using [`wrapping_add`] instead if these constraints are
/// difficult to satisfy. The only advantage of this method is that it
/// enables more aggressive compiler optimizations.
///
/// [`wrapping_add`]: #method.wrapping_add
/// [allocated object]: crate::ptr#allocated-object
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let s: &str = "123";
/// let ptr: *const u8 = s.as_ptr();
///
/// unsafe {
/// println!("{}", *ptr.add(1) as char);
/// println!("{}", *ptr.add(2) as char);
/// }
/// ```
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[must_use = "returns a new pointer rather than modifying its argument"]
#[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn add(self, count: usize) -> Self
where
T: Sized,
{
// SAFETY: the caller must uphold the safety contract for `offset`.
unsafe { self.offset(count as isize) }
}
/// Calculates the offset from a pointer in bytes (convenience for `.byte_offset(count as isize)`).
///
/// `count` is in units of bytes.
///
/// This is purely a convenience for casting to a `u8` pointer and
/// using [add][pointer::add] on it. See that method for documentation
/// and safety requirements.
///
/// For non-`Sized` pointees this operation changes only the data pointer,
/// leaving the metadata untouched.
#[must_use]
#[inline(always)]
#[unstable(feature = "pointer_byte_offsets", issue = "96283")]
#[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn byte_add(self, count: usize) -> Self {
// SAFETY: the caller must uphold the safety contract for `add`.
unsafe { self.cast::<u8>().add(count).with_metadata_of(self) }
}
/// Calculates the offset from a pointer (convenience for
/// `.offset((count as isize).wrapping_neg())`).
///
/// `count` is in units of T; e.g., a `count` of 3 represents a pointer
/// offset of `3 * size_of::<T>()` bytes.
///
/// # Safety
///
/// If any of the following conditions are violated, the result is Undefined
/// Behavior:
///
/// * Both the starting and resulting pointer must be either in bounds or one
/// byte past the end of the same [allocated object].
///
/// * The computed offset cannot exceed `isize::MAX` **bytes**.
///
/// * The offset being in bounds cannot rely on "wrapping around" the address
/// space. That is, the infinite-precision sum must fit in a usize.
///
/// The compiler and standard library generally tries to ensure allocations
/// never reach a size where an offset is a concern. For instance, `Vec`
/// and `Box` ensure they never allocate more than `isize::MAX` bytes, so
/// `vec.as_ptr().add(vec.len()).sub(vec.len())` is always safe.
///
/// Most platforms fundamentally can't even construct such an allocation.
/// For instance, no known 64-bit platform can ever serve a request
/// for 2<sup>63</sup> bytes due to page-table limitations or splitting the address space.
/// However, some 32-bit and 16-bit platforms may successfully serve a request for
/// more than `isize::MAX` bytes with things like Physical Address
/// Extension. As such, memory acquired directly from allocators or memory
/// mapped files *may* be too large to handle with this function.
///
/// Consider using [`wrapping_sub`] instead if these constraints are
/// difficult to satisfy. The only advantage of this method is that it
/// enables more aggressive compiler optimizations.
///
/// [`wrapping_sub`]: #method.wrapping_sub
/// [allocated object]: crate::ptr#allocated-object
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let s: &str = "123";
///
/// unsafe {
/// let end: *const u8 = s.as_ptr().add(3);
/// println!("{}", *end.sub(1) as char);
/// println!("{}", *end.sub(2) as char);
/// }
/// ```
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[must_use = "returns a new pointer rather than modifying its argument"]
#[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
#[inline]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn sub(self, count: usize) -> Self
where
T: Sized,
{
// SAFETY: the caller must uphold the safety contract for `offset`.
unsafe { self.offset((count as isize).wrapping_neg()) }
}
/// Calculates the offset from a pointer in bytes (convenience for
/// `.byte_offset((count as isize).wrapping_neg())`).
///
/// `count` is in units of bytes.
///
/// This is purely a convenience for casting to a `u8` pointer and
/// using [sub][pointer::sub] on it. See that method for documentation
/// and safety requirements.
///
/// For non-`Sized` pointees this operation changes only the data pointer,
/// leaving the metadata untouched.
#[must_use]
#[inline(always)]
#[unstable(feature = "pointer_byte_offsets", issue = "96283")]
#[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn byte_sub(self, count: usize) -> Self {
// SAFETY: the caller must uphold the safety contract for `sub`.
unsafe { self.cast::<u8>().sub(count).with_metadata_of(self) }
}
/// Calculates the offset from a pointer using wrapping arithmetic.
/// (convenience for `.wrapping_offset(count as isize)`)
///
/// `count` is in units of T; e.g., a `count` of 3 represents a pointer
/// offset of `3 * size_of::<T>()` bytes.
///
/// # Safety
///
/// This operation itself is always safe, but using the resulting pointer is not.
///
/// The resulting pointer "remembers" the [allocated object] that `self` points to; it must not
/// be used to read or write other allocated objects.
///
/// In other words, `let z = x.wrapping_add((y as usize) - (x as usize))` does *not* make `z`
/// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
/// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless
/// `x` and `y` point into the same allocated object.
///
/// Compared to [`add`], this method basically delays the requirement of staying within the
/// same allocated object: [`add`] is immediate Undefined Behavior when crossing object
/// boundaries; `wrapping_add` produces a pointer but still leads to Undefined Behavior if a
/// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`add`]
/// can be optimized better and is thus preferable in performance-sensitive code.
///
/// The delayed check only considers the value of the pointer that was dereferenced, not the
/// intermediate values used during the computation of the final result. For example,
/// `x.wrapping_add(o).wrapping_sub(o)` is always the same as `x`. In other words, leaving the
/// allocated object and then re-entering it later is permitted.
///
/// [`add`]: #method.add
/// [allocated object]: crate::ptr#allocated-object
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// // Iterate using a raw pointer in increments of two elements
/// let data = [1u8, 2, 3, 4, 5];
/// let mut ptr: *const u8 = data.as_ptr();
/// let step = 2;
/// let end_rounded_up = ptr.wrapping_add(6);
///
/// // This loop prints "1, 3, 5, "
/// while ptr != end_rounded_up {
/// unsafe {
/// print!("{}, ", *ptr);
/// }
/// ptr = ptr.wrapping_add(step);
/// }
/// ```
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[must_use = "returns a new pointer rather than modifying its argument"]
#[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
#[inline(always)]
pub const fn wrapping_add(self, count: usize) -> Self
where
T: Sized,
{
self.wrapping_offset(count as isize)
}
/// Calculates the offset from a pointer in bytes using wrapping arithmetic.
/// (convenience for `.wrapping_byte_offset(count as isize)`)
///
/// `count` is in units of bytes.
///
/// This is purely a convenience for casting to a `u8` pointer and
/// using [wrapping_add][pointer::wrapping_add] on it. See that method for documentation.
///
/// For non-`Sized` pointees this operation changes only the data pointer,
/// leaving the metadata untouched.
#[must_use]
#[inline(always)]
#[unstable(feature = "pointer_byte_offsets", issue = "96283")]
#[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
pub const fn wrapping_byte_add(self, count: usize) -> Self {
self.cast::<u8>().wrapping_add(count).with_metadata_of(self)
}
/// Calculates the offset from a pointer using wrapping arithmetic.
/// (convenience for `.wrapping_offset((count as isize).wrapping_neg())`)
///
/// `count` is in units of T; e.g., a `count` of 3 represents a pointer
/// offset of `3 * size_of::<T>()` bytes.
///
/// # Safety
///
/// This operation itself is always safe, but using the resulting pointer is not.
///
/// The resulting pointer "remembers" the [allocated object] that `self` points to; it must not
/// be used to read or write other allocated objects.
///
/// In other words, `let z = x.wrapping_sub((x as usize) - (y as usize))` does *not* make `z`
/// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
/// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless
/// `x` and `y` point into the same allocated object.
///
/// Compared to [`sub`], this method basically delays the requirement of staying within the
/// same allocated object: [`sub`] is immediate Undefined Behavior when crossing object
/// boundaries; `wrapping_sub` produces a pointer but still leads to Undefined Behavior if a
/// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`sub`]
/// can be optimized better and is thus preferable in performance-sensitive code.
///
/// The delayed check only considers the value of the pointer that was dereferenced, not the
/// intermediate values used during the computation of the final result. For example,
/// `x.wrapping_add(o).wrapping_sub(o)` is always the same as `x`. In other words, leaving the
/// allocated object and then re-entering it later is permitted.
///
/// [`sub`]: #method.sub
/// [allocated object]: crate::ptr#allocated-object
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// // Iterate using a raw pointer in increments of two elements (backwards)
/// let data = [1u8, 2, 3, 4, 5];
/// let mut ptr: *const u8 = data.as_ptr();
/// let start_rounded_down = ptr.wrapping_sub(2);
/// ptr = ptr.wrapping_add(4);
/// let step = 2;
/// // This loop prints "5, 3, 1, "
/// while ptr != start_rounded_down {
/// unsafe {
/// print!("{}, ", *ptr);
/// }
/// ptr = ptr.wrapping_sub(step);
/// }
/// ```
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[must_use = "returns a new pointer rather than modifying its argument"]
#[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
#[inline]
pub const fn wrapping_sub(self, count: usize) -> Self
where
T: Sized,
{
self.wrapping_offset((count as isize).wrapping_neg())
}
/// Calculates the offset from a pointer in bytes using wrapping arithmetic.
/// (convenience for `.wrapping_offset((count as isize).wrapping_neg())`)
///
/// `count` is in units of bytes.
///
/// This is purely a convenience for casting to a `u8` pointer and
/// using [wrapping_sub][pointer::wrapping_sub] on it. See that method for documentation.
///
/// For non-`Sized` pointees this operation changes only the data pointer,
/// leaving the metadata untouched.
#[must_use]
#[inline(always)]
#[unstable(feature = "pointer_byte_offsets", issue = "96283")]
#[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
pub const fn wrapping_byte_sub(self, count: usize) -> Self {
self.cast::<u8>().wrapping_sub(count).with_metadata_of(self)
}
/// Reads the value from `self` without moving it. This leaves the
/// memory in `self` unchanged.
///
/// See [`ptr::read`] for safety concerns and examples.
///
/// [`ptr::read`]: crate::ptr::read()
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[rustc_const_unstable(feature = "const_ptr_read", issue = "80377")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn read(self) -> T
where
T: Sized,
{
// SAFETY: the caller must uphold the safety contract for ``.
unsafe { read(self) }
}
/// Performs a volatile read of the value from `self` without moving it. This
/// leaves the memory in `self` unchanged.
///
/// Volatile operations are intended to act on I/O memory, and are guaranteed
/// to not be elided or reordered by the compiler across other volatile
/// operations.
///
/// See [`ptr::read_volatile`] for safety concerns and examples.
///
/// [`ptr::read_volatile`]: crate::ptr::read_volatile()
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub unsafe fn read_volatile(self) -> T
where
T: Sized,
{
// SAFETY: the caller must uphold the safety contract for `read_volatile`.
unsafe { read_volatile(self) }
}
/// Reads the value from `self` without moving it. This leaves the
/// memory in `self` unchanged.
///
/// Unlike `read`, the pointer may be unaligned.
///
/// See [`ptr::read_unaligned`] for safety concerns and examples.
///
/// [`ptr::read_unaligned`]: crate::ptr::read_unaligned()
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[rustc_const_unstable(feature = "const_ptr_read", issue = "80377")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn read_unaligned(self) -> T
where
T: Sized,
{
// SAFETY: the caller must uphold the safety contract for `read_unaligned`.
unsafe { read_unaligned(self) }
}
/// Copies `count * size_of<T>` bytes from `self` to `dest`. The source
/// and destination may overlap.
///
/// NOTE: this has the *same* argument order as [`ptr::copy`].
///
/// See [`ptr::copy`] for safety concerns and examples.
///
/// [`ptr::copy`]: crate::ptr::copy()
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn copy_to(self, dest: *mut T, count: usize)
where
T: Sized,
{
// SAFETY: the caller must uphold the safety contract for `copy`.
unsafe { copy(self, dest, count) }
}
/// Copies `count * size_of<T>` bytes from `self` to `dest`. The source
/// and destination may *not* overlap.
///
/// NOTE: this has the *same* argument order as [`ptr::copy_nonoverlapping`].
///
/// See [`ptr::copy_nonoverlapping`] for safety concerns and examples.
///
/// [`ptr::copy_nonoverlapping`]: crate::ptr::copy_nonoverlapping()
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn copy_to_nonoverlapping(self, dest: *mut T, count: usize)
where
T: Sized,
{
// SAFETY: the caller must uphold the safety contract for `copy_nonoverlapping`.
unsafe { copy_nonoverlapping(self, dest, count) }
}
/// Copies `count * size_of<T>` bytes from `src` to `self`. The source
/// and destination may overlap.
///
/// NOTE: this has the *opposite* argument order of [`ptr::copy`].
///
/// See [`ptr::copy`] for safety concerns and examples.
///
/// [`ptr::copy`]: crate::ptr::copy()
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn copy_from(self, src: *const T, count: usize)
where
T: Sized,
{
// SAFETY: the caller must uphold the safety contract for `copy`.
unsafe { copy(src, self, count) }
}
/// Copies `count * size_of<T>` bytes from `src` to `self`. The source
/// and destination may *not* overlap.
///
/// NOTE: this has the *opposite* argument order of [`ptr::copy_nonoverlapping`].
///
/// See [`ptr::copy_nonoverlapping`] for safety concerns and examples.
///
/// [`ptr::copy_nonoverlapping`]: crate::ptr::copy_nonoverlapping()
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn copy_from_nonoverlapping(self, src: *const T, count: usize)
where
T: Sized,
{
// SAFETY: the caller must uphold the safety contract for `copy_nonoverlapping`.
unsafe { copy_nonoverlapping(src, self, count) }
}
/// Executes the destructor (if any) of the pointed-to value.
///
/// See [`ptr::drop_in_place`] for safety concerns and examples.
///
/// [`ptr::drop_in_place`]: crate::ptr::drop_in_place()
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[inline(always)]
pub unsafe fn drop_in_place(self) {
// SAFETY: the caller must uphold the safety contract for `drop_in_place`.
unsafe { drop_in_place(self) }
}
/// Overwrites a memory location with the given value without reading or
/// dropping the old value.
///
/// See [`ptr::write`] for safety concerns and examples.
///
/// [`ptr::write`]: crate::ptr::write()
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[rustc_const_unstable(feature = "const_ptr_write", issue = "86302")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn write(self, val: T)
where
T: Sized,
{
// SAFETY: the caller must uphold the safety contract for `write`.
unsafe { write(self, val) }
}
/// Invokes memset on the specified pointer, setting `count * size_of::<T>()`
/// bytes of memory starting at `self` to `val`.
///
/// See [`ptr::write_bytes`] for safety concerns and examples.
///
/// [`ptr::write_bytes`]: crate::ptr::write_bytes()
#[doc(alias = "memset")]
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[rustc_const_unstable(feature = "const_ptr_write", issue = "86302")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn write_bytes(self, val: u8, count: usize)
where
T: Sized,
{
// SAFETY: the caller must uphold the safety contract for `write_bytes`.
unsafe { write_bytes(self, val, count) }
}
/// Performs a volatile write of a memory location with the given value without
/// reading or dropping the old value.
///
/// Volatile operations are intended to act on I/O memory, and are guaranteed
/// to not be elided or reordered by the compiler across other volatile
/// operations.
///
/// See [`ptr::write_volatile`] for safety concerns and examples.
///
/// [`ptr::write_volatile`]: crate::ptr::write_volatile()
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub unsafe fn write_volatile(self, val: T)
where
T: Sized,
{
// SAFETY: the caller must uphold the safety contract for `write_volatile`.
unsafe { write_volatile(self, val) }
}
/// Overwrites a memory location with the given value without reading or
/// dropping the old value.
///
/// Unlike `write`, the pointer may be unaligned.
///
/// See [`ptr::write_unaligned`] for safety concerns and examples.
///
/// [`ptr::write_unaligned`]: crate::ptr::write_unaligned()
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[rustc_const_unstable(feature = "const_ptr_write", issue = "86302")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn write_unaligned(self, val: T)
where
T: Sized,
{
// SAFETY: the caller must uphold the safety contract for `write_unaligned`.
unsafe { write_unaligned(self, val) }
}
/// Replaces the value at `self` with `src`, returning the old
/// value, without dropping either.
///
/// See [`ptr::replace`] for safety concerns and examples.
///
/// [`ptr::replace`]: crate::ptr::replace()
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[inline(always)]
pub unsafe fn replace(self, src: T) -> T
where
T: Sized,
{
// SAFETY: the caller must uphold the safety contract for `replace`.
unsafe { replace(self, src) }
}
/// Swaps the values at two mutable locations of the same type, without
/// deinitializing either. They may overlap, unlike `mem::swap` which is
/// otherwise equivalent.
///
/// See [`ptr::swap`] for safety concerns and examples.
///
/// [`ptr::swap`]: crate::ptr::swap()
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[rustc_const_unstable(feature = "const_swap", issue = "83163")]
#[inline(always)]
pub const unsafe fn swap(self, with: *mut T)
where
T: Sized,
{
// SAFETY: the caller must uphold the safety contract for `swap`.
unsafe { swap(self, with) }
}
/// Computes the offset that needs to be applied to the pointer in order to make it aligned to
/// `align`.
///
/// If it is not possible to align the pointer, the implementation returns
/// `usize::MAX`. It is permissible for the implementation to *always*
/// return `usize::MAX`. Only your algorithm's performance can depend
/// on getting a usable offset here, not its correctness.
///
/// The offset is expressed in number of `T` elements, and not bytes. The value returned can be
/// used with the `wrapping_add` method.
///
/// There are no guarantees whatsoever that offsetting the pointer will not overflow or go
/// beyond the allocation that the pointer points into. It is up to the caller to ensure that
/// the returned offset is correct in all terms other than alignment.
///
/// # Panics
///
/// The function panics if `align` is not a power-of-two.
///
/// # Examples
///
/// Accessing adjacent `u8` as `u16`
///
/// ```
/// use std::mem::align_of;
///
/// # unsafe {
/// let mut x = [5_u8, 6, 7, 8, 9];
/// let ptr = x.as_mut_ptr();
/// let offset = ptr.align_offset(align_of::<u16>());
///
/// if offset < x.len() - 1 {
/// let u16_ptr = ptr.add(offset).cast::<u16>();
/// *u16_ptr = 0;
///
/// assert!(x == [0, 0, 7, 8, 9] || x == [5, 0, 0, 8, 9]);
/// } else {
/// // while the pointer can be aligned via `offset`, it would point
/// // outside the allocation
/// }
/// # }
/// ```
#[must_use]
#[inline]
#[stable(feature = "align_offset", since = "1.36.0")]
#[rustc_const_unstable(feature = "const_align_offset", issue = "90962")]
pub const fn align_offset(self, align: usize) -> usize
where
T: Sized,
{
if !align.is_power_of_two() {
panic!("align_offset: align is not a power-of-two");
}
#[cfg(bootstrap)]
{
fn rt_impl<T>(p: *mut T, align: usize) -> usize {
// SAFETY: `align` has been checked to be a power of 2 above
unsafe { align_offset(p, align) }
}
const fn ctfe_impl<T>(_: *mut T, _: usize) -> usize {
usize::MAX
}
// SAFETY:
// It is permissible for `align_offset` to always return `usize::MAX`,
// algorithm correctness can not depend on `align_offset` returning non-max values.
//
// As such the behaviour can't change after replacing `align_offset` with `usize::MAX`, only performance can.
unsafe { intrinsics::const_eval_select((self, align), ctfe_impl, rt_impl) }
}
#[cfg(not(bootstrap))]
{
// SAFETY: `align` has been checked to be a power of 2 above
unsafe { align_offset(self, align) }
}
}
/// Returns whether the pointer is properly aligned for `T`.
///
/// # Examples
///
/// Basic usage:
/// ```
/// #![feature(pointer_is_aligned)]
/// #![feature(pointer_byte_offsets)]
///
/// // On some platforms, the alignment of i32 is less than 4.
/// #[repr(align(4))]
/// struct AlignedI32(i32);
///
/// let mut data = AlignedI32(42);
/// let ptr = &mut data as *mut AlignedI32;
///
/// assert!(ptr.is_aligned());
/// assert!(!ptr.wrapping_byte_add(1).is_aligned());
/// ```
///
/// # At compiletime
/// **Note: Alignment at compiletime is experimental and subject to change. See the
/// [tracking issue] for details.**
///
/// At compiletime, the compiler may not know where a value will end up in memory.
/// Calling this function on a pointer created from a reference at compiletime will only
/// return `true` if the pointer is guaranteed to be aligned. This means that the pointer
/// is never aligned if cast to a type with a stricter alignment than the reference's
/// underlying allocation.
///
#[cfg_attr(bootstrap, doc = "```ignore")]
#[cfg_attr(not(bootstrap), doc = "```")]
/// #![feature(pointer_is_aligned)]
/// #![feature(const_pointer_is_aligned)]
/// #![feature(const_mut_refs)]
///
/// // On some platforms, the alignment of primitives is less than their size.
/// #[repr(align(4))]
/// struct AlignedI32(i32);
/// #[repr(align(8))]
/// struct AlignedI64(i64);
///
/// const _: () = {
/// let mut data = AlignedI32(42);
/// let ptr = &mut data as *mut AlignedI32;
/// assert!(ptr.is_aligned());
///
/// // At runtime either `ptr1` or `ptr2` would be aligned, but at compiletime neither is aligned.
/// let ptr1 = ptr.cast::<AlignedI64>();
/// let ptr2 = ptr.wrapping_add(1).cast::<AlignedI64>();
/// assert!(!ptr1.is_aligned());
/// assert!(!ptr2.is_aligned());
/// };
/// ```
///
/// Due to this behavior, it is possible that a runtime pointer derived from a compiletime
/// pointer is aligned, even if the compiletime pointer wasn't aligned.
///
#[cfg_attr(bootstrap, doc = "```ignore")]
#[cfg_attr(not(bootstrap), doc = "```")]
/// #![feature(pointer_is_aligned)]
/// #![feature(const_pointer_is_aligned)]
///
/// // On some platforms, the alignment of primitives is less than their size.
/// #[repr(align(4))]
/// struct AlignedI32(i32);
/// #[repr(align(8))]
/// struct AlignedI64(i64);
///
/// // At compiletime, neither `COMPTIME_PTR` nor `COMPTIME_PTR + 1` is aligned.
/// // Also, note that mutable references are not allowed in the final value of constants.
/// const COMPTIME_PTR: *mut AlignedI32 = (&AlignedI32(42) as *const AlignedI32).cast_mut();
/// const _: () = assert!(!COMPTIME_PTR.cast::<AlignedI64>().is_aligned());
/// const _: () = assert!(!COMPTIME_PTR.wrapping_add(1).cast::<AlignedI64>().is_aligned());
///
/// // At runtime, either `runtime_ptr` or `runtime_ptr + 1` is aligned.
/// let runtime_ptr = COMPTIME_PTR;
/// assert_ne!(
/// runtime_ptr.cast::<AlignedI64>().is_aligned(),
/// runtime_ptr.wrapping_add(1).cast::<AlignedI64>().is_aligned(),
/// );
/// ```
///
/// If a pointer is created from a fixed address, this function behaves the same during
/// runtime and compiletime.
///
#[cfg_attr(bootstrap, doc = "```ignore")]
#[cfg_attr(not(bootstrap), doc = "```")]
/// #![feature(pointer_is_aligned)]
/// #![feature(const_pointer_is_aligned)]
///
/// // On some platforms, the alignment of primitives is less than their size.
/// #[repr(align(4))]
/// struct AlignedI32(i32);
/// #[repr(align(8))]
/// struct AlignedI64(i64);
///
/// const _: () = {
/// let ptr = 40 as *mut AlignedI32;
/// assert!(ptr.is_aligned());
///
/// // For pointers with a known address, runtime and compiletime behavior are identical.
/// let ptr1 = ptr.cast::<AlignedI64>();
/// let ptr2 = ptr.wrapping_add(1).cast::<AlignedI64>();
/// assert!(ptr1.is_aligned());
/// assert!(!ptr2.is_aligned());
/// };
/// ```
///
/// [tracking issue]: https://github.com/rust-lang/rust/issues/104203
#[must_use]
#[inline]
#[unstable(feature = "pointer_is_aligned", issue = "96284")]
#[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "104203")]
pub const fn is_aligned(self) -> bool
where
T: Sized,
{
self.is_aligned_to(mem::align_of::<T>())
}
/// Returns whether the pointer is aligned to `align`.
///
/// For non-`Sized` pointees this operation considers only the data pointer,
/// ignoring the metadata.
///
/// # Panics
///
/// The function panics if `align` is not a power-of-two (this includes 0).
///
/// # Examples
///
/// Basic usage:
/// ```
/// #![feature(pointer_is_aligned)]
/// #![feature(pointer_byte_offsets)]
///
/// // On some platforms, the alignment of i32 is less than 4.
/// #[repr(align(4))]
/// struct AlignedI32(i32);
///
/// let mut data = AlignedI32(42);
/// let ptr = &mut data as *mut AlignedI32;
///
/// assert!(ptr.is_aligned_to(1));
/// assert!(ptr.is_aligned_to(2));
/// assert!(ptr.is_aligned_to(4));
///
/// assert!(ptr.wrapping_byte_add(2).is_aligned_to(2));
/// assert!(!ptr.wrapping_byte_add(2).is_aligned_to(4));
///
/// assert_ne!(ptr.is_aligned_to(8), ptr.wrapping_add(1).is_aligned_to(8));
/// ```
///
/// # At compiletime
/// **Note: Alignment at compiletime is experimental and subject to change. See the
/// [tracking issue] for details.**
///
/// At compiletime, the compiler may not know where a value will end up in memory.
/// Calling this function on a pointer created from a reference at compiletime will only
/// return `true` if the pointer is guaranteed to be aligned. This means that the pointer
/// cannot be stricter aligned than the reference's underlying allocation.
///
#[cfg_attr(bootstrap, doc = "```ignore")]
#[cfg_attr(not(bootstrap), doc = "```")]
/// #![feature(pointer_is_aligned)]
/// #![feature(const_pointer_is_aligned)]
/// #![feature(const_mut_refs)]
///
/// // On some platforms, the alignment of i32 is less than 4.
/// #[repr(align(4))]
/// struct AlignedI32(i32);
///
/// const _: () = {
/// let mut data = AlignedI32(42);
/// let ptr = &mut data as *mut AlignedI32;
///
/// assert!(ptr.is_aligned_to(1));
/// assert!(ptr.is_aligned_to(2));
/// assert!(ptr.is_aligned_to(4));
///
/// // At compiletime, we know for sure that the pointer isn't aligned to 8.
/// assert!(!ptr.is_aligned_to(8));
/// assert!(!ptr.wrapping_add(1).is_aligned_to(8));
/// };
/// ```
///
/// Due to this behavior, it is possible that a runtime pointer derived from a compiletime
/// pointer is aligned, even if the compiletime pointer wasn't aligned.
///
#[cfg_attr(bootstrap, doc = "```ignore")]
#[cfg_attr(not(bootstrap), doc = "```")]
/// #![feature(pointer_is_aligned)]
/// #![feature(const_pointer_is_aligned)]
///
/// // On some platforms, the alignment of i32 is less than 4.
/// #[repr(align(4))]
/// struct AlignedI32(i32);
///
/// // At compiletime, neither `COMPTIME_PTR` nor `COMPTIME_PTR + 1` is aligned.
/// // Also, note that mutable references are not allowed in the final value of constants.
/// const COMPTIME_PTR: *mut AlignedI32 = (&AlignedI32(42) as *const AlignedI32).cast_mut();
/// const _: () = assert!(!COMPTIME_PTR.is_aligned_to(8));
/// const _: () = assert!(!COMPTIME_PTR.wrapping_add(1).is_aligned_to(8));
///
/// // At runtime, either `runtime_ptr` or `runtime_ptr + 1` is aligned.
/// let runtime_ptr = COMPTIME_PTR;
/// assert_ne!(
/// runtime_ptr.is_aligned_to(8),
/// runtime_ptr.wrapping_add(1).is_aligned_to(8),
/// );
/// ```
///
/// If a pointer is created from a fixed address, this function behaves the same during
/// runtime and compiletime.
///
#[cfg_attr(bootstrap, doc = "```ignore")]
#[cfg_attr(not(bootstrap), doc = "```")]
/// #![feature(pointer_is_aligned)]
/// #![feature(const_pointer_is_aligned)]
///
/// const _: () = {
/// let ptr = 40 as *mut u8;
/// assert!(ptr.is_aligned_to(1));
/// assert!(ptr.is_aligned_to(2));
/// assert!(ptr.is_aligned_to(4));
/// assert!(ptr.is_aligned_to(8));
/// assert!(!ptr.is_aligned_to(16));
/// };
/// ```
///
/// [tracking issue]: https://github.com/rust-lang/rust/issues/104203
#[must_use]
#[inline]
#[unstable(feature = "pointer_is_aligned", issue = "96284")]
#[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "104203")]
pub const fn is_aligned_to(self, align: usize) -> bool {
if !align.is_power_of_two() {
panic!("is_aligned_to: align is not a power-of-two");
}
// We can't use the address of `self` in a `const fn`, so we use `align_offset` instead.
// The cast to `()` is used to
// 1. deal with fat pointers; and
// 2. ensure that `align_offset` doesn't actually try to compute an offset.
self.cast::<()>().align_offset(align) == 0
}
}
impl<T> *mut [T] {
/// Returns the length of a raw slice.
///
/// The returned value is the number of **elements**, not the number of bytes.
///
/// This function is safe, even when the raw slice cannot be cast to a slice
/// reference because the pointer is null or unaligned.
///
/// # Examples
///
/// ```rust
/// #![feature(slice_ptr_len)]
/// use std::ptr;
///
/// let slice: *mut [i8] = ptr::slice_from_raw_parts_mut(ptr::null_mut(), 3);
/// assert_eq!(slice.len(), 3);
/// ```
#[inline(always)]
#[unstable(feature = "slice_ptr_len", issue = "71146")]
#[rustc_const_unstable(feature = "const_slice_ptr_len", issue = "71146")]
pub const fn len(self) -> usize {
metadata(self)
}
/// Returns `true` if the raw slice has a length of 0.
///
/// # Examples
///
/// ```
/// #![feature(slice_ptr_len)]
///
/// let mut a = [1, 2, 3];
/// let ptr = &mut a as *mut [_];
/// assert!(!ptr.is_empty());
/// ```
#[inline(always)]
#[unstable(feature = "slice_ptr_len", issue = "71146")]
#[rustc_const_unstable(feature = "const_slice_ptr_len", issue = "71146")]
pub const fn is_empty(self) -> bool {
self.len() == 0
}
/// Divides one mutable raw slice into two at an index.
///
/// The first will contain all indices from `[0, mid)` (excluding
/// the index `mid` itself) and the second will contain all
/// indices from `[mid, len)` (excluding the index `len` itself).
///
/// # Panics
///
/// Panics if `mid > len`.
///
/// # Safety
///
/// `mid` must be [in-bounds] of the underlying [allocated object].
/// Which means `self` must be dereferenceable and span a single allocation
/// that is at least `mid * size_of::<T>()` bytes long. Not upholding these
/// requirements is *[undefined behavior]* even if the resulting pointers are not used.
///
/// Since `len` being in-bounds it is not a safety invariant of `*mut [T]` the
/// safety requirements of this method are the same as for [`split_at_mut_unchecked`].
/// The explicit bounds check is only as useful as `len` is correct.
///
/// [`split_at_mut_unchecked`]: #method.split_at_mut_unchecked
/// [in-bounds]: #method.add
/// [allocated object]: crate::ptr#allocated-object
/// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
///
/// # Examples
///
/// ```
/// #![feature(raw_slice_split)]
/// #![feature(slice_ptr_get)]
///
/// let mut v = [1, 0, 3, 0, 5, 6];
/// let ptr = &mut v as *mut [_];
/// unsafe {
/// let (left, right) = ptr.split_at_mut(2);
/// assert_eq!(&*left, [1, 0]);
/// assert_eq!(&*right, [3, 0, 5, 6]);
/// }
/// ```
#[inline(always)]
#[track_caller]
#[unstable(feature = "raw_slice_split", issue = "95595")]
pub unsafe fn split_at_mut(self, mid: usize) -> (*mut [T], *mut [T]) {
assert!(mid <= self.len());
// SAFETY: The assert above is only a safety-net as long as `self.len()` is correct
// The actual safety requirements of this function are the same as for `split_at_mut_unchecked`
unsafe { self.split_at_mut_unchecked(mid) }
}
/// Divides one mutable raw slice into two at an index, without doing bounds checking.
///
/// The first will contain all indices from `[0, mid)` (excluding
/// the index `mid` itself) and the second will contain all
/// indices from `[mid, len)` (excluding the index `len` itself).
///
/// # Safety
///
/// `mid` must be [in-bounds] of the underlying [allocated object].
/// Which means `self` must be dereferenceable and span a single allocation
/// that is at least `mid * size_of::<T>()` bytes long. Not upholding these
/// requirements is *[undefined behavior]* even if the resulting pointers are not used.
///
/// [in-bounds]: #method.add
/// [out-of-bounds index]: #method.add
/// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
///
/// # Examples
///
/// ```
/// #![feature(raw_slice_split)]
///
/// let mut v = [1, 0, 3, 0, 5, 6];
/// // scoped to restrict the lifetime of the borrows
/// unsafe {
/// let ptr = &mut v as *mut [_];
/// let (left, right) = ptr.split_at_mut_unchecked(2);
/// assert_eq!(&*left, [1, 0]);
/// assert_eq!(&*right, [3, 0, 5, 6]);
/// (&mut *left)[1] = 2;
/// (&mut *right)[1] = 4;
/// }
/// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
/// ```
#[inline(always)]
#[unstable(feature = "raw_slice_split", issue = "95595")]
pub unsafe fn split_at_mut_unchecked(self, mid: usize) -> (*mut [T], *mut [T]) {
let len = self.len();
let ptr = self.as_mut_ptr();
// SAFETY: Caller must pass a valid pointer and an index that is in-bounds.
let tail = unsafe { ptr.add(mid) };
(
crate::ptr::slice_from_raw_parts_mut(ptr, mid),
crate::ptr::slice_from_raw_parts_mut(tail, len - mid),
)
}
/// Returns a raw pointer to the slice's buffer.
///
/// This is equivalent to casting `self` to `*mut T`, but more type-safe.
///
/// # Examples
///
/// ```rust
/// #![feature(slice_ptr_get)]
/// use std::ptr;
///
/// let slice: *mut [i8] = ptr::slice_from_raw_parts_mut(ptr::null_mut(), 3);
/// assert_eq!(slice.as_mut_ptr(), ptr::null_mut());
/// ```
#[inline(always)]
#[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 *mut T
}
/// 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.
///
/// [out-of-bounds index]: #method.add
/// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
///
/// # Examples
///
/// ```
/// #![feature(slice_ptr_get)]
///
/// let x = &mut [1, 2, 4] as *mut [i32];
///
/// unsafe {
/// assert_eq!(x.get_unchecked_mut(1), x.as_mut_ptr().add(1));
/// }
/// ```
#[unstable(feature = "slice_ptr_get", issue = "74265")]
#[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
#[inline(always)]
pub const unsafe fn get_unchecked_mut<I>(self, index: I) -> *mut I::Output
where
I: ~const SliceIndex<[T]>,
{
// SAFETY: the caller ensures that `self` is dereferenceable and `index` in-bounds.
unsafe { index.get_unchecked_mut(self) }
}
/// Returns `None` if the pointer is null, or else returns a shared slice to
/// the value wrapped in `Some`. 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`]: #method.as_ref-1
/// [`as_uninit_slice_mut`]: #method.as_uninit_slice_mut
///
/// # Safety
///
/// When calling this method, you have to ensure that *either* the pointer is null *or*
/// 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
/// [allocated object]: crate::ptr#allocated-object
#[inline]
#[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) -> Option<&'a [MaybeUninit<T>]> {
if self.is_null() {
None
} else {
// SAFETY: the caller must uphold the safety contract for `as_uninit_slice`.
Some(unsafe { slice::from_raw_parts(self as *const MaybeUninit<T>, self.len()) })
}
}
/// Returns `None` if the pointer is null, or else returns a unique slice to
/// the value wrapped in `Some`. 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`]: #method.as_mut
/// [`as_uninit_slice`]: #method.as_uninit_slice-1
///
/// # Safety
///
/// When calling this method, you have to ensure that *either* the pointer is null *or*
/// 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
/// [allocated object]: crate::ptr#allocated-object
#[inline]
#[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) -> Option<&'a mut [MaybeUninit<T>]> {
if self.is_null() {
None
} else {
// SAFETY: the caller must uphold the safety contract for `as_uninit_slice_mut`.
Some(unsafe { slice::from_raw_parts_mut(self as *mut MaybeUninit<T>, self.len()) })
}
}
}
// Equality for pointers
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> PartialEq for *mut T {
#[inline(always)]
fn eq(&self, other: &*mut T) -> bool {
*self == *other
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Eq for *mut T {}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Ord for *mut T {
#[inline]
fn cmp(&self, other: &*mut T) -> Ordering {
if self < other {
Less
} else if self == other {
Equal
} else {
Greater
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> PartialOrd for *mut T {
#[inline(always)]
fn partial_cmp(&self, other: &*mut T) -> Option<Ordering> {
Some(self.cmp(other))
}
#[inline(always)]
fn lt(&self, other: &*mut T) -> bool {
*self < *other
}
#[inline(always)]
fn le(&self, other: &*mut T) -> bool {
*self <= *other
}
#[inline(always)]
fn gt(&self, other: &*mut T) -> bool {
*self > *other
}
#[inline(always)]
fn ge(&self, other: &*mut T) -> bool {
*self >= *other
}
}