library/core/src/ptr/mut_ptr.rs

   1 use super::*;
   2 use crate::cmp::Ordering::{self, Equal, Greater, Less};
   3 use crate::intrinsics;
   4 use crate::slice::{self, SliceIndex};
   5
   6 #[lang = "mut_ptr"]
   7 impl<T: ?Sized> *mut T {
   8     /// Returns `true` if the pointer is null.
   9     ///
  10     /// Note that unsized types have many possible null pointers, as only the
  11     /// raw data pointer is considered, not their length, vtable, etc.
  12     /// Therefore, two pointers that are null may still not compare equal to
  13     /// each other.
  14     ///
  15     /// ## Behavior during const evaluation
  16     ///
  17     /// When this function is used during const evaluation, it may return `false` for pointers
  18     /// that turn out to be null at runtime. Specifically, when a pointer to some memory
  19     /// is offset beyond its bounds in such a way that the resulting pointer is null,
  20     /// the function will still return `false`. There is no way for CTFE to know
  21     /// the absolute position of that memory, so we cannot tell if the pointer is
  22     /// null or not.
  23     ///
  24     /// # Examples
  25     ///
  26     /// Basic usage:
  27     ///
  28     /// ```
  29     /// let mut s = [1, 2, 3];
  30     /// let ptr: *mut u32 = s.as_mut_ptr();
  31     /// assert!(!ptr.is_null());
  32     /// ```
  33     #[stable(feature = "rust1", since = "1.0.0")]
  34     #[rustc_const_unstable(feature = "const_ptr_is_null", issue = "74939")]
  35     #[inline]
  36     pub const fn is_null(self) -> bool {
  37         // Compare via a cast to a thin pointer, so fat pointers are only
  38         // considering their "data" part for null-ness.
  39         (self as *mut u8).guaranteed_eq(null_mut())
  40     }
  41
  42     /// Casts to a pointer of another type.
  43     #[stable(feature = "ptr_cast", since = "1.38.0")]
  44     #[rustc_const_stable(feature = "const_ptr_cast", since = "1.38.0")]
  45     #[inline]
  46     pub const fn cast<U>(self) -> *mut U {
  47         self as _
  48     }
  49
  50     /// Decompose a (possibly wide) pointer into is address and metadata components.
  51     ///
  52     /// The pointer can be later reconstructed with [`from_raw_parts_mut`].
  53     #[cfg(not(bootstrap))]
  54     #[unstable(feature = "ptr_metadata", issue = "81513")]
  55     #[rustc_const_unstable(feature = "ptr_metadata", issue = "81513")]
  56     #[inline]
  57     pub const fn to_raw_parts(self) -> (*mut (), <T as super::Pointee>::Metadata) {
  58         (self.cast(), super::metadata(self))
  59     }
  60
  61     /// Returns `None` if the pointer is null, or else returns a shared reference to
  62     /// the value wrapped in `Some`. If the value may be uninitialized, [`as_uninit_ref`]
  63     /// must be used instead.
  64     ///
  65     /// For the mutable counterpart see [`as_mut`].
  66     ///
  67     /// [`as_uninit_ref`]: #method.as_uninit_ref-1
  68     /// [`as_mut`]: #method.as_mut
  69     ///
  70     /// # Safety
  71     ///
  72     /// When calling this method, you have to ensure that *either* the pointer is NULL *or*
  73     /// all of the following is true:
  74     ///
  75     /// * The pointer must be properly aligned.
  76     ///
  77     /// * It must be "dereferencable" in the sense defined in [the module documentation].
  78     ///
  79     /// * The pointer must point to an initialized instance of `T`.
  80     ///
  81     /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
  82     ///   arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
  83     ///   In particular, for the duration of this lifetime, the memory the pointer points to must
  84     ///   not get mutated (except inside `UnsafeCell`).
  85     ///
  86     /// This applies even if the result of this method is unused!
  87     /// (The part about being initialized is not yet fully decided, but until
  88     /// it is, the only safe approach is to ensure that they are indeed initialized.)
  89     ///
  90     /// [the module documentation]: crate::ptr#safety
  91     ///
  92     /// # Examples
  93     ///
  94     /// Basic usage:
  95     ///
  96     /// ```
  97     /// let ptr: *mut u8 = &mut 10u8 as *mut u8;
  98     ///
  99     /// unsafe {
 100     ///     if let Some(val_back) = ptr.as_ref() {
 101     ///         println!("We got back the value: {}!", val_back);
 102     ///     }
 103     /// }
 104     /// ```
 105     ///
 106     /// # Null-unchecked version
 107     ///
 108     /// If you are sure the pointer can never be null and are looking for some kind of
 109     /// `as_ref_unchecked` that returns the `&T` instead of `Option<&T>`, know that you can
 110     /// dereference the pointer directly.
 111     ///
 112     /// ```
 113     /// let ptr: *mut u8 = &mut 10u8 as *mut u8;
 114     ///
 115     /// unsafe {
 116     ///     let val_back = &*ptr;
 117     ///     println!("We got back the value: {}!", val_back);
 118     /// }
 119     /// ```
 120     #[stable(feature = "ptr_as_ref", since = "1.9.0")]
 121     #[inline]
 122     pub unsafe fn as_ref<'a>(self) -> Option<&'a T> {
 123         // SAFETY: the caller must guarantee that `self` is valid for a
 124         // reference if it isn't null.
 125         if self.is_null() { None } else { unsafe { Some(&*self) } }
 126     }
 127
 128     /// Returns `None` if the pointer is null, or else returns a shared reference to
 129     /// the value wrapped in `Some`. In contrast to [`as_ref`], this does not require
 130     /// that the value has to be initialized.
 131     ///
 132     /// For the mutable counterpart see [`as_uninit_mut`].
 133     ///
 134     /// [`as_ref`]: #method.as_ref-1
 135     /// [`as_uninit_mut`]: #method.as_uninit_mut
 136     ///
 137     /// # Safety
 138     ///
 139     /// When calling this method, you have to ensure that *either* the pointer is NULL *or*
 140     /// all of the following is true:
 141     ///
 142     /// * The pointer must be properly aligned.
 143     ///
 144     /// * It must be "dereferencable" in the sense defined in [the module documentation].
 145     ///
 146     /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
 147     ///   arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
 148     ///   In particular, for the duration of this lifetime, the memory the pointer points to must
 149     ///   not get mutated (except inside `UnsafeCell`).
 150     ///
 151     /// This applies even if the result of this method is unused!
 152     ///
 153     /// [the module documentation]: crate::ptr#safety
 154     ///
 155     /// # Examples
 156     ///
 157     /// Basic usage:
 158     ///
 159     /// ```
 160     /// #![feature(ptr_as_uninit)]
 161     ///
 162     /// let ptr: *mut u8 = &mut 10u8 as *mut u8;
 163     ///
 164     /// unsafe {
 165     ///     if let Some(val_back) = ptr.as_uninit_ref() {
 166     ///         println!("We got back the value: {}!", val_back.assume_init());
 167     ///     }
 168     /// }
 169     /// ```
 170     #[inline]
 171     #[unstable(feature = "ptr_as_uninit", issue = "75402")]
 172     pub unsafe fn as_uninit_ref<'a>(self) -> Option<&'a MaybeUninit<T>>
 173     where
 174         T: Sized,
 175     {
 176         // SAFETY: the caller must guarantee that `self` meets all the
 177         // requirements for a reference.
 178         if self.is_null() { None } else { Some(unsafe { &*(self as *const MaybeUninit<T>) }) }
 179     }
 180
 181     /// Calculates the offset from a pointer.
 182     ///
 183     /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
 184     /// offset of `3 * size_of::<T>()` bytes.
 185     ///
 186     /// # Safety
 187     ///
 188     /// If any of the following conditions are violated, the result is Undefined
 189     /// Behavior:
 190     ///
 191     /// * Both the starting and resulting pointer must be either in bounds or one
 192     ///   byte past the end of the same allocated object. Note that in Rust,
 193     ///   every (stack-allocated) variable is considered a separate allocated object.
 194     ///
 195     /// * The computed offset, **in bytes**, cannot overflow an `isize`.
 196     ///
 197     /// * The offset being in bounds cannot rely on "wrapping around" the address
 198     ///   space. That is, the infinite-precision sum, **in bytes** must fit in a usize.
 199     ///
 200     /// The compiler and standard library generally tries to ensure allocations
 201     /// never reach a size where an offset is a concern. For instance, `Vec`
 202     /// and `Box` ensure they never allocate more than `isize::MAX` bytes, so
 203     /// `vec.as_ptr().add(vec.len())` is always safe.
 204     ///
 205     /// Most platforms fundamentally can't even construct such an allocation.
 206     /// For instance, no known 64-bit platform can ever serve a request
 207     /// for 2<sup>63</sup> bytes due to page-table limitations or splitting the address space.
 208     /// However, some 32-bit and 16-bit platforms may successfully serve a request for
 209     /// more than `isize::MAX` bytes with things like Physical Address
 210     /// Extension. As such, memory acquired directly from allocators or memory
 211     /// mapped files *may* be too large to handle with this function.
 212     ///
 213     /// Consider using [`wrapping_offset`] instead if these constraints are
 214     /// difficult to satisfy. The only advantage of this method is that it
 215     /// enables more aggressive compiler optimizations.
 216     ///
 217     /// [`wrapping_offset`]: #method.wrapping_offset
 218     ///
 219     /// # Examples
 220     ///
 221     /// Basic usage:
 222     ///
 223     /// ```
 224     /// let mut s = [1, 2, 3];
 225     /// let ptr: *mut u32 = s.as_mut_ptr();
 226     ///
 227     /// unsafe {
 228     ///     println!("{}", *ptr.offset(1));
 229     ///     println!("{}", *ptr.offset(2));
 230     /// }
 231     /// ```
 232     #[stable(feature = "rust1", since = "1.0.0")]
 233     #[must_use = "returns a new pointer rather than modifying its argument"]
 234     #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
 235     #[inline]
 236     pub const unsafe fn offset(self, count: isize) -> *mut T
 237     where
 238         T: Sized,
 239     {
 240         // SAFETY: the caller must uphold the safety contract for `offset`.
 241         // The obtained pointer is valid for writes since the caller must
 242         // guarantee that it points to the same allocated object as `self`.
 243         unsafe { intrinsics::offset(self, count) as *mut T }
 244     }
 245
 246     /// Calculates the offset from a pointer using wrapping arithmetic.
 247     /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
 248     /// offset of `3 * size_of::<T>()` bytes.
 249     ///
 250     /// # Safety
 251     ///
 252     /// This operation itself is always safe, but using the resulting pointer is not.
 253     ///
 254     /// The resulting pointer remains attached to the same allocated object that `self` points to.
 255     /// It may *not* be used to access a different allocated object. Note that in Rust, every
 256     /// (stack-allocated) variable is considered a separate allocated object.
 257     ///
 258     /// In other words, `let z = x.wrapping_offset((y as isize) - (x as isize))` does *not* make `z`
 259     /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
 260     /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless
 261     /// `x` and `y` point into the same allocated object.
 262     ///
 263     /// Compared to [`offset`], this method basically delays the requirement of staying within the
 264     /// same allocated object: [`offset`] is immediate Undefined Behavior when crossing object
 265     /// boundaries; `wrapping_offset` produces a pointer but still leads to Undefined Behavior if a
 266     /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`offset`]
 267     /// can be optimized better and is thus preferable in performance-sensitive code.
 268     ///
 269     /// The delayed check only considers the value of the pointer that was dereferenced, not the
 270     /// intermediate values used during the computation of the final result. For example,
 271     /// `x.wrapping_offset(o).wrapping_offset(o.wrapping_neg())` is always the same as `x`. In other
 272     /// words, leaving the allocated object and then re-entering it later is permitted.
 273     ///
 274     /// If you need to cross object boundaries, cast the pointer to an integer and
 275     /// do the arithmetic there.
 276     ///
 277     /// [`offset`]: #method.offset
 278     ///
 279     /// # Examples
 280     ///
 281     /// Basic usage:
 282     ///
 283     /// ```
 284     /// // Iterate using a raw pointer in increments of two elements
 285     /// let mut data = [1u8, 2, 3, 4, 5];
 286     /// let mut ptr: *mut u8 = data.as_mut_ptr();
 287     /// let step = 2;
 288     /// let end_rounded_up = ptr.wrapping_offset(6);
 289     ///
 290     /// while ptr != end_rounded_up {
 291     ///     unsafe {
 292     ///         *ptr = 0;
 293     ///     }
 294     ///     ptr = ptr.wrapping_offset(step);
 295     /// }
 296     /// assert_eq!(&data, &[0, 2, 0, 4, 0]);
 297     /// ```
 298     #[stable(feature = "ptr_wrapping_offset", since = "1.16.0")]
 299     #[must_use = "returns a new pointer rather than modifying its argument"]
 300     #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
 301     #[inline]
 302     pub const fn wrapping_offset(self, count: isize) -> *mut T
 303     where
 304         T: Sized,
 305     {
 306         // SAFETY: the `arith_offset` intrinsic has no prerequisites to be called.
 307         unsafe { intrinsics::arith_offset(self, count) as *mut T }
 308     }
 309
 310     /// Returns `None` if the pointer is null, or else returns a unique reference to
 311     /// the value wrapped in `Some`. If the value may be uninitialized, [`as_uninit_mut`]
 312     /// must be used instead.
 313     ///
 314     /// For the shared counterpart see [`as_ref`].
 315     ///
 316     /// [`as_uninit_mut`]: #method.as_uninit_mut
 317     /// [`as_ref`]: #method.as_ref-1
 318     ///
 319     /// # Safety
 320     ///
 321     /// When calling this method, you have to ensure that *either* the pointer is NULL *or*
 322     /// all of the following is true:
 323     ///
 324     /// * The pointer must be properly aligned.
 325     ///
 326     /// * It must be "dereferencable" in the sense defined in [the module documentation].
 327     ///
 328     /// * The pointer must point to an initialized instance of `T`.
 329     ///
 330     /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
 331     ///   arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
 332     ///   In particular, for the duration of this lifetime, the memory the pointer points to must
 333     ///   not get accessed (read or written) through any other pointer.
 334     ///
 335     /// This applies even if the result of this method is unused!
 336     /// (The part about being initialized is not yet fully decided, but until
 337     /// it is, the only safe approach is to ensure that they are indeed initialized.)
 338     ///
 339     /// [the module documentation]: crate::ptr#safety
 340     ///
 341     /// # Examples
 342     ///
 343     /// Basic usage:
 344     ///
 345     /// ```
 346     /// let mut s = [1, 2, 3];
 347     /// let ptr: *mut u32 = s.as_mut_ptr();
 348     /// let first_value = unsafe { ptr.as_mut().unwrap() };
 349     /// *first_value = 4;
 350     /// # assert_eq!(s, [4, 2, 3]);
 351     /// println!("{:?}", s); // It'll print: "[4, 2, 3]".
 352     /// ```
 353     ///
 354     /// # Null-unchecked version
 355     ///
 356     /// If you are sure the pointer can never be null and are looking for some kind of
 357     /// `as_mut_unchecked` that returns the `&mut T` instead of `Option<&mut T>`, know that
 358     /// you can dereference the pointer directly.
 359     ///
 360     /// ```
 361     /// let mut s = [1, 2, 3];
 362     /// let ptr: *mut u32 = s.as_mut_ptr();
 363     /// let first_value = unsafe { &mut *ptr };
 364     /// *first_value = 4;
 365     /// # assert_eq!(s, [4, 2, 3]);
 366     /// println!("{:?}", s); // It'll print: "[4, 2, 3]".
 367     /// ```
 368     #[stable(feature = "ptr_as_ref", since = "1.9.0")]
 369     #[inline]
 370     pub unsafe fn as_mut<'a>(self) -> Option<&'a mut T> {
 371         // SAFETY: the caller must guarantee that `self` is be valid for
 372         // a mutable reference if it isn't null.
 373         if self.is_null() { None } else { unsafe { Some(&mut *self) } }
 374     }
 375
 376     /// Returns `None` if the pointer is null, or else returns a unique reference to
 377     /// the value wrapped in `Some`. In contrast to [`as_mut`], this does not require
 378     /// that the value has to be initialized.
 379     ///
 380     /// For the shared counterpart see [`as_uninit_ref`].
 381     ///
 382     /// [`as_mut`]: #method.as_mut
 383     /// [`as_uninit_ref`]: #method.as_uninit_ref-1
 384     ///
 385     /// # Safety
 386     ///
 387     /// When calling this method, you have to ensure that *either* the pointer is NULL *or*
 388     /// all of the following is true:
 389     ///
 390     /// * The pointer must be properly aligned.
 391     ///
 392     /// * It must be "dereferencable" in the sense defined in [the module documentation].
 393     ///
 394     /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
 395     ///   arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
 396     ///   In particular, for the duration of this lifetime, the memory the pointer points to must
 397     ///   not get accessed (read or written) through any other pointer.
 398     ///
 399     /// This applies even if the result of this method is unused!
 400     ///
 401     /// [the module documentation]: crate::ptr#safety
 402     #[inline]
 403     #[unstable(feature = "ptr_as_uninit", issue = "75402")]
 404     pub unsafe fn as_uninit_mut<'a>(self) -> Option<&'a mut MaybeUninit<T>>
 405     where
 406         T: Sized,
 407     {
 408         // SAFETY: the caller must guarantee that `self` meets all the
 409         // requirements for a reference.
 410         if self.is_null() { None } else { Some(unsafe { &mut *(self as *mut MaybeUninit<T>) }) }
 411     }
 412
 413     /// Returns whether two pointers are guaranteed to be equal.
 414     ///
 415     /// At runtime this function behaves like `self == other`.
 416     /// However, in some contexts (e.g., compile-time evaluation),
 417     /// it is not always possible to determine equality of two pointers, so this function may
 418     /// spuriously return `false` for pointers that later actually turn out to be equal.
 419     /// But when it returns `true`, the pointers are guaranteed to be equal.
 420     ///
 421     /// This function is the mirror of [`guaranteed_ne`], but not its inverse. There are pointer
 422     /// comparisons for which both functions return `false`.
 423     ///
 424     /// [`guaranteed_ne`]: #method.guaranteed_ne
 425     ///
 426     /// The return value may change depending on the compiler version and unsafe code may not
 427     /// rely on the result of this function for soundness. It is suggested to only use this function
 428     /// for performance optimizations where spurious `false` return values by this function do not
 429     /// affect the outcome, but just the performance.
 430     /// The consequences of using this method to make runtime and compile-time code behave
 431     /// differently have not been explored. This method should not be used to introduce such
 432     /// differences, and it should also not be stabilized before we have a better understanding
 433     /// of this issue.
 434     #[unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
 435     #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
 436     #[inline]
 437     pub const fn guaranteed_eq(self, other: *mut T) -> bool
 438     where
 439         T: Sized,
 440     {
 441         intrinsics::ptr_guaranteed_eq(self as *const _, other as *const _)
 442     }
 443
 444     /// Returns whether two pointers are guaranteed to be unequal.
 445     ///
 446     /// At runtime this function behaves like `self != other`.
 447     /// However, in some contexts (e.g., compile-time evaluation),
 448     /// it is not always possible to determine the inequality of two pointers, so this function may
 449     /// spuriously return `false` for pointers that later actually turn out to be unequal.
 450     /// But when it returns `true`, the pointers are guaranteed to be unequal.
 451     ///
 452     /// This function is the mirror of [`guaranteed_eq`], but not its inverse. There are pointer
 453     /// comparisons for which both functions return `false`.
 454     ///
 455     /// [`guaranteed_eq`]: #method.guaranteed_eq
 456     ///
 457     /// The return value may change depending on the compiler version and unsafe code may not
 458     /// rely on the result of this function for soundness. It is suggested to only use this function
 459     /// for performance optimizations where spurious `false` return values by this function do not
 460     /// affect the outcome, but just the performance.
 461     /// The consequences of using this method to make runtime and compile-time code behave
 462     /// differently have not been explored. This method should not be used to introduce such
 463     /// differences, and it should also not be stabilized before we have a better understanding
 464     /// of this issue.
 465     #[unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
 466     #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
 467     #[inline]
 468     pub const unsafe fn guaranteed_ne(self, other: *mut T) -> bool
 469     where
 470         T: Sized,
 471     {
 472         intrinsics::ptr_guaranteed_ne(self as *const _, other as *const _)
 473     }
 474
 475     /// Calculates the distance between two pointers. The returned value is in
 476     /// units of T: the distance in bytes is divided by `mem::size_of::<T>()`.
 477     ///
 478     /// This function is the inverse of [`offset`].
 479     ///
 480     /// [`offset`]: #method.offset-1
 481     ///
 482     /// # Safety
 483     ///
 484     /// If any of the following conditions are violated, the result is Undefined
 485     /// Behavior:
 486     ///
 487     /// * Both the starting and other pointer must be either in bounds or one
 488     ///   byte past the end of the same allocated object. Note that in Rust,
 489     ///   every (stack-allocated) variable is considered a separate allocated object.
 490     ///
 491     /// * Both pointers must be *derived from* a pointer to the same object.
 492     ///   (See below for an example.)
 493     ///
 494     /// * The distance between the pointers, in bytes, must be an exact multiple
 495     ///   of the size of `T`.
 496     ///
 497     /// * The distance between the pointers, **in bytes**, cannot overflow an `isize`.
 498     ///
 499     /// * The distance being in bounds cannot rely on "wrapping around" the address space.
 500     ///
 501     /// Rust types are never larger than `isize::MAX` and Rust allocations never wrap around the
 502     /// address space, so two pointers within some value of any Rust type `T` will always satisfy
 503     /// the last two conditions. The standard library also generally ensures that allocations
 504     /// never reach a size where an offset is a concern. For instance, `Vec` and `Box` ensure they
 505     /// never allocate more than `isize::MAX` bytes, so `ptr_into_vec.offset_from(vec.as_ptr())`
 506     /// always satisfies the last two conditions.
 507     ///
 508     /// Most platforms fundamentally can't even construct such a large allocation.
 509     /// For instance, no known 64-bit platform can ever serve a request
 510     /// for 2<sup>63</sup> bytes due to page-table limitations or splitting the address space.
 511     /// However, some 32-bit and 16-bit platforms may successfully serve a request for
 512     /// more than `isize::MAX` bytes with things like Physical Address
 513     /// Extension. As such, memory acquired directly from allocators or memory
 514     /// mapped files *may* be too large to handle with this function.
 515     /// (Note that [`offset`] and [`add`] also have a similar limitation and hence cannot be used on
 516     /// such large allocations either.)
 517     ///
 518     /// [`add`]: #method.add
 519     ///
 520     /// # Panics
 521     ///
 522     /// This function panics if `T` is a Zero-Sized Type ("ZST").
 523     ///
 524     /// # Examples
 525     ///
 526     /// Basic usage:
 527     ///
 528     /// ```
 529     /// let mut a = [0; 5];
 530     /// let ptr1: *mut i32 = &mut a[1];
 531     /// let ptr2: *mut i32 = &mut a[3];
 532     /// unsafe {
 533     ///     assert_eq!(ptr2.offset_from(ptr1), 2);
 534     ///     assert_eq!(ptr1.offset_from(ptr2), -2);
 535     ///     assert_eq!(ptr1.offset(2), ptr2);
 536     ///     assert_eq!(ptr2.offset(-2), ptr1);
 537     /// }
 538     /// ```
 539     ///
 540     /// *Incorrect* usage:
 541     ///
 542     /// ```rust,no_run
 543     /// let ptr1 = Box::into_raw(Box::new(0u8));
 544     /// let ptr2 = Box::into_raw(Box::new(1u8));
 545     /// let diff = (ptr2 as isize).wrapping_sub(ptr1 as isize);
 546     /// // Make ptr2_other an "alias" of ptr2, but derived from ptr1.
 547     /// let ptr2_other = (ptr1 as *mut u8).wrapping_offset(diff);
 548     /// assert_eq!(ptr2 as usize, ptr2_other as usize);
 549     /// // Since ptr2_other and ptr2 are derived from pointers to different objects,
 550     /// // computing their offset is undefined behavior, even though
 551     /// // they point to the same address!
 552     /// unsafe {
 553     ///     let zero = ptr2_other.offset_from(ptr2); // Undefined Behavior
 554     /// }
 555     /// ```
 556     #[stable(feature = "ptr_offset_from", since = "1.47.0")]
 557     #[rustc_const_unstable(feature = "const_ptr_offset_from", issue = "41079")]
 558     #[inline]
 559     pub const unsafe fn offset_from(self, origin: *const T) -> isize
 560     where
 561         T: Sized,
 562     {
 563         // SAFETY: the caller must uphold the safety contract for `offset_from`.
 564         unsafe { (self as *const T).offset_from(origin) }
 565     }
 566
 567     /// Calculates the offset from a pointer (convenience for `.offset(count as isize)`).
 568     ///
 569     /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
 570     /// offset of `3 * size_of::<T>()` bytes.
 571     ///
 572     /// # Safety
 573     ///
 574     /// If any of the following conditions are violated, the result is Undefined
 575     /// Behavior:
 576     ///
 577     /// * Both the starting and resulting pointer must be either in bounds or one
 578     ///   byte past the end of the same allocated object. Note that in Rust,
 579     ///   every (stack-allocated) variable is considered a separate allocated object.
 580     ///
 581     /// * The computed offset, **in bytes**, cannot overflow an `isize`.
 582     ///
 583     /// * The offset being in bounds cannot rely on "wrapping around" the address
 584     ///   space. That is, the infinite-precision sum must fit in a `usize`.
 585     ///
 586     /// The compiler and standard library generally tries to ensure allocations
 587     /// never reach a size where an offset is a concern. For instance, `Vec`
 588     /// and `Box` ensure they never allocate more than `isize::MAX` bytes, so
 589     /// `vec.as_ptr().add(vec.len())` is always safe.
 590     ///
 591     /// Most platforms fundamentally can't even construct such an allocation.
 592     /// For instance, no known 64-bit platform can ever serve a request
 593     /// for 2<sup>63</sup> bytes due to page-table limitations or splitting the address space.
 594     /// However, some 32-bit and 16-bit platforms may successfully serve a request for
 595     /// more than `isize::MAX` bytes with things like Physical Address
 596     /// Extension. As such, memory acquired directly from allocators or memory
 597     /// mapped files *may* be too large to handle with this function.
 598     ///
 599     /// Consider using [`wrapping_add`] instead if these constraints are
 600     /// difficult to satisfy. The only advantage of this method is that it
 601     /// enables more aggressive compiler optimizations.
 602     ///
 603     /// [`wrapping_add`]: #method.wrapping_add
 604     ///
 605     /// # Examples
 606     ///
 607     /// Basic usage:
 608     ///
 609     /// ```
 610     /// let s: &str = "123";
 611     /// let ptr: *const u8 = s.as_ptr();
 612     ///
 613     /// unsafe {
 614     ///     println!("{}", *ptr.add(1) as char);
 615     ///     println!("{}", *ptr.add(2) as char);
 616     /// }
 617     /// ```
 618     #[stable(feature = "pointer_methods", since = "1.26.0")]
 619     #[must_use = "returns a new pointer rather than modifying its argument"]
 620     #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
 621     #[inline]
 622     pub const unsafe fn add(self, count: usize) -> Self
 623     where
 624         T: Sized,
 625     {
 626         // SAFETY: the caller must uphold the safety contract for `offset`.
 627         unsafe { self.offset(count as isize) }
 628     }
 629
 630     /// Calculates the offset from a pointer (convenience for
 631     /// `.offset((count as isize).wrapping_neg())`).
 632     ///
 633     /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
 634     /// offset of `3 * size_of::<T>()` bytes.
 635     ///
 636     /// # Safety
 637     ///
 638     /// If any of the following conditions are violated, the result is Undefined
 639     /// Behavior:
 640     ///
 641     /// * Both the starting and resulting pointer must be either in bounds or one
 642     ///   byte past the end of the same allocated object. Note that in Rust,
 643     ///   every (stack-allocated) variable is considered a separate allocated object.
 644     ///
 645     /// * The computed offset cannot exceed `isize::MAX` **bytes**.
 646     ///
 647     /// * The offset being in bounds cannot rely on "wrapping around" the address
 648     ///   space. That is, the infinite-precision sum must fit in a usize.
 649     ///
 650     /// The compiler and standard library generally tries to ensure allocations
 651     /// never reach a size where an offset is a concern. For instance, `Vec`
 652     /// and `Box` ensure they never allocate more than `isize::MAX` bytes, so
 653     /// `vec.as_ptr().add(vec.len()).sub(vec.len())` is always safe.
 654     ///
 655     /// Most platforms fundamentally can't even construct such an allocation.
 656     /// For instance, no known 64-bit platform can ever serve a request
 657     /// for 2<sup>63</sup> bytes due to page-table limitations or splitting the address space.
 658     /// However, some 32-bit and 16-bit platforms may successfully serve a request for
 659     /// more than `isize::MAX` bytes with things like Physical Address
 660     /// Extension. As such, memory acquired directly from allocators or memory
 661     /// mapped files *may* be too large to handle with this function.
 662     ///
 663     /// Consider using [`wrapping_sub`] instead if these constraints are
 664     /// difficult to satisfy. The only advantage of this method is that it
 665     /// enables more aggressive compiler optimizations.
 666     ///
 667     /// [`wrapping_sub`]: #method.wrapping_sub
 668     ///
 669     /// # Examples
 670     ///
 671     /// Basic usage:
 672     ///
 673     /// ```
 674     /// let s: &str = "123";
 675     ///
 676     /// unsafe {
 677     ///     let end: *const u8 = s.as_ptr().add(3);
 678     ///     println!("{}", *end.sub(1) as char);
 679     ///     println!("{}", *end.sub(2) as char);
 680     /// }
 681     /// ```
 682     #[stable(feature = "pointer_methods", since = "1.26.0")]
 683     #[must_use = "returns a new pointer rather than modifying its argument"]
 684     #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
 685     #[inline]
 686     pub const unsafe fn sub(self, count: usize) -> Self
 687     where
 688         T: Sized,
 689     {
 690         // SAFETY: the caller must uphold the safety contract for `offset`.
 691         unsafe { self.offset((count as isize).wrapping_neg()) }
 692     }
 693
 694     /// Calculates the offset from a pointer using wrapping arithmetic.
 695     /// (convenience for `.wrapping_offset(count as isize)`)
 696     ///
 697     /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
 698     /// offset of `3 * size_of::<T>()` bytes.
 699     ///
 700     /// # Safety
 701     ///
 702     /// This operation itself is always safe, but using the resulting pointer is not.
 703     ///
 704     /// The resulting pointer remains attached to the same allocated object that `self` points to.
 705     /// It may *not* be used to access a different allocated object. Note that in Rust, every
 706     /// (stack-allocated) variable is considered a separate allocated object.
 707     ///
 708     /// In other words, `let z = x.wrapping_add((y as usize) - (x as usize))` does *not* make `z`
 709     /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
 710     /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless
 711     /// `x` and `y` point into the same allocated object.
 712     ///
 713     /// Compared to [`add`], this method basically delays the requirement of staying within the
 714     /// same allocated object: [`add`] is immediate Undefined Behavior when crossing object
 715     /// boundaries; `wrapping_add` produces a pointer but still leads to Undefined Behavior if a
 716     /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`add`]
 717     /// can be optimized better and is thus preferable in performance-sensitive code.
 718     ///
 719     /// The delayed check only considers the value of the pointer that was dereferenced, not the
 720     /// intermediate values used during the computation of the final result. For example,
 721     /// `x.wrapping_add(o).wrapping_sub(o)` is always the same as `x`. In other words, leaving the
 722     /// allocated object and then re-entering it later is permitted.
 723     ///
 724     /// If you need to cross object boundaries, cast the pointer to an integer and
 725     /// do the arithmetic there.
 726     ///
 727     /// [`add`]: #method.add
 728     ///
 729     /// # Examples
 730     ///
 731     /// Basic usage:
 732     ///
 733     /// ```
 734     /// // Iterate using a raw pointer in increments of two elements
 735     /// let data = [1u8, 2, 3, 4, 5];
 736     /// let mut ptr: *const u8 = data.as_ptr();
 737     /// let step = 2;
 738     /// let end_rounded_up = ptr.wrapping_add(6);
 739     ///
 740     /// // This loop prints "1, 3, 5, "
 741     /// while ptr != end_rounded_up {
 742     ///     unsafe {
 743     ///         print!("{}, ", *ptr);
 744     ///     }
 745     ///     ptr = ptr.wrapping_add(step);
 746     /// }
 747     /// ```
 748     #[stable(feature = "pointer_methods", since = "1.26.0")]
 749     #[must_use = "returns a new pointer rather than modifying its argument"]
 750     #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
 751     #[inline]
 752     pub const fn wrapping_add(self, count: usize) -> Self
 753     where
 754         T: Sized,
 755     {
 756         self.wrapping_offset(count as isize)
 757     }
 758
 759     /// Calculates the offset from a pointer using wrapping arithmetic.
 760     /// (convenience for `.wrapping_offset((count as isize).wrapping_neg())`)
 761     ///
 762     /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
 763     /// offset of `3 * size_of::<T>()` bytes.
 764     ///
 765     /// # Safety
 766     ///
 767     /// This operation itself is always safe, but using the resulting pointer is not.
 768     ///
 769     /// The resulting pointer remains attached to the same allocated object that `self` points to.
 770     /// It may *not* be used to access a different allocated object. Note that in Rust, every
 771     /// (stack-allocated) variable is considered a separate allocated object.
 772     ///
 773     /// In other words, `let z = x.wrapping_sub((x as usize) - (y as usize))` does *not* make `z`
 774     /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
 775     /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless
 776     /// `x` and `y` point into the same allocated object.
 777     ///
 778     /// Compared to [`sub`], this method basically delays the requirement of staying within the
 779     /// same allocated object: [`sub`] is immediate Undefined Behavior when crossing object
 780     /// boundaries; `wrapping_sub` produces a pointer but still leads to Undefined Behavior if a
 781     /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`sub`]
 782     /// can be optimized better and is thus preferable in performance-sensitive code.
 783     ///
 784     /// The delayed check only considers the value of the pointer that was dereferenced, not the
 785     /// intermediate values used during the computation of the final result. For example,
 786     /// `x.wrapping_add(o).wrapping_sub(o)` is always the same as `x`. In other words, leaving the
 787     /// allocated object and then re-entering it later is permitted.
 788     ///
 789     /// If you need to cross object boundaries, cast the pointer to an integer and
 790     /// do the arithmetic there.
 791     ///
 792     /// [`sub`]: #method.sub
 793     ///
 794     /// # Examples
 795     ///
 796     /// Basic usage:
 797     ///
 798     /// ```
 799     /// // Iterate using a raw pointer in increments of two elements (backwards)
 800     /// let data = [1u8, 2, 3, 4, 5];
 801     /// let mut ptr: *const u8 = data.as_ptr();
 802     /// let start_rounded_down = ptr.wrapping_sub(2);
 803     /// ptr = ptr.wrapping_add(4);
 804     /// let step = 2;
 805     /// // This loop prints "5, 3, 1, "
 806     /// while ptr != start_rounded_down {
 807     ///     unsafe {
 808     ///         print!("{}, ", *ptr);
 809     ///     }
 810     ///     ptr = ptr.wrapping_sub(step);
 811     /// }
 812     /// ```
 813     #[stable(feature = "pointer_methods", since = "1.26.0")]
 814     #[must_use = "returns a new pointer rather than modifying its argument"]
 815     #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
 816     #[inline]
 817     pub const fn wrapping_sub(self, count: usize) -> Self
 818     where
 819         T: Sized,
 820     {
 821         self.wrapping_offset((count as isize).wrapping_neg())
 822     }
 823
 824     /// Sets the pointer value to `ptr`.
 825     ///
 826     /// In case `self` is a (fat) pointer to an unsized type, this operation
 827     /// will only affect the pointer part, whereas for (thin) pointers to
 828     /// sized types, this has the same effect as a simple assignment.
 829     ///
 830     /// The resulting pointer will have provenance of `val`, i.e., for a fat
 831     /// pointer, this operation is semantically the same as creating a new
 832     /// fat pointer with the data pointer value of `val` but the metadata of
 833     /// `self`.
 834     ///
 835     /// # Examples
 836     ///
 837     /// This function is primarily useful for allowing byte-wise pointer
 838     /// arithmetic on potentially fat pointers:
 839     ///
 840     /// ```
 841     /// #![feature(set_ptr_value)]
 842     /// # use core::fmt::Debug;
 843     /// let mut arr: [i32; 3] = [1, 2, 3];
 844     /// let mut ptr = &mut arr[0] as *mut dyn Debug;
 845     /// let thin = ptr as *mut u8;
 846     /// unsafe {
 847     ///     ptr = ptr.set_ptr_value(thin.add(8));
 848     ///     # assert_eq!(*(ptr as *mut i32), 3);
 849     ///     println!("{:?}", &*ptr); // will print "3"
 850     /// }
 851     /// ```
 852     #[unstable(feature = "set_ptr_value", issue = "75091")]
 853     #[must_use = "returns a new pointer rather than modifying its argument"]
 854     #[inline]
 855     pub fn set_ptr_value(mut self, val: *mut u8) -> Self {
 856         let thin = &mut self as *mut *mut T as *mut *mut u8;
 857         // SAFETY: In case of a thin pointer, this operations is identical
 858         // to a simple assignment. In case of a fat pointer, with the current
 859         // fat pointer layout implementation, the first field of such a
 860         // pointer is always the data pointer, which is likewise assigned.
 861         unsafe { *thin = val };
 862         self
 863     }
 864
 865     /// Reads the value from `self` without moving it. This leaves the
 866     /// memory in `self` unchanged.
 867     ///
 868     /// See [`ptr::read`] for safety concerns and examples.
 869     ///
 870     /// [`ptr::read`]: crate::ptr::read()
 871     #[stable(feature = "pointer_methods", since = "1.26.0")]
 872     #[rustc_const_unstable(feature = "const_ptr_read", issue = "80377")]
 873     #[inline]
 874     pub const unsafe fn read(self) -> T
 875     where
 876         T: Sized,
 877     {
 878         // SAFETY: the caller must uphold the safety contract for ``.
 879         unsafe { read(self) }
 880     }
 881
 882     /// Performs a volatile read of the value from `self` without moving it. This
 883     /// leaves the memory in `self` unchanged.
 884     ///
 885     /// Volatile operations are intended to act on I/O memory, and are guaranteed
 886     /// to not be elided or reordered by the compiler across other volatile
 887     /// operations.
 888     ///
 889     /// See [`ptr::read_volatile`] for safety concerns and examples.
 890     ///
 891     /// [`ptr::read_volatile`]: crate::ptr::read_volatile()
 892     #[stable(feature = "pointer_methods", since = "1.26.0")]
 893     #[inline]
 894     pub unsafe fn read_volatile(self) -> T
 895     where
 896         T: Sized,
 897     {
 898         // SAFETY: the caller must uphold the safety contract for `read_volatile`.
 899         unsafe { read_volatile(self) }
 900     }
 901
 902     /// Reads the value from `self` without moving it. This leaves the
 903     /// memory in `self` unchanged.
 904     ///
 905     /// Unlike `read`, the pointer may be unaligned.
 906     ///
 907     /// See [`ptr::read_unaligned`] for safety concerns and examples.
 908     ///
 909     /// [`ptr::read_unaligned`]: crate::ptr::read_unaligned()
 910     #[stable(feature = "pointer_methods", since = "1.26.0")]
 911     #[rustc_const_unstable(feature = "const_ptr_read", issue = "80377")]
 912     #[inline]
 913     pub const unsafe fn read_unaligned(self) -> T
 914     where
 915         T: Sized,
 916     {
 917         // SAFETY: the caller must uphold the safety contract for `read_unaligned`.
 918         unsafe { read_unaligned(self) }
 919     }
 920
 921     /// Copies `count * size_of<T>` bytes from `self` to `dest`. The source
 922     /// and destination may overlap.
 923     ///
 924     /// NOTE: this has the *same* argument order as [`ptr::copy`].
 925     ///
 926     /// See [`ptr::copy`] for safety concerns and examples.
 927     ///
 928     /// [`ptr::copy`]: crate::ptr::copy()
 929     #[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
 930     #[stable(feature = "pointer_methods", since = "1.26.0")]
 931     #[inline]
 932     pub const unsafe fn copy_to(self, dest: *mut T, count: usize)
 933     where
 934         T: Sized,
 935     {
 936         // SAFETY: the caller must uphold the safety contract for `copy`.
 937         unsafe { copy(self, dest, count) }
 938     }
 939
 940     /// Copies `count * size_of<T>` bytes from `self` to `dest`. The source
 941     /// and destination may *not* overlap.
 942     ///
 943     /// NOTE: this has the *same* argument order as [`ptr::copy_nonoverlapping`].
 944     ///
 945     /// See [`ptr::copy_nonoverlapping`] for safety concerns and examples.
 946     ///
 947     /// [`ptr::copy_nonoverlapping`]: crate::ptr::copy_nonoverlapping()
 948     #[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
 949     #[stable(feature = "pointer_methods", since = "1.26.0")]
 950     #[inline]
 951     pub const unsafe fn copy_to_nonoverlapping(self, dest: *mut T, count: usize)
 952     where
 953         T: Sized,
 954     {
 955         // SAFETY: the caller must uphold the safety contract for `copy_nonoverlapping`.
 956         unsafe { copy_nonoverlapping(self, dest, count) }
 957     }
 958
 959     /// Copies `count * size_of<T>` bytes from `src` to `self`. The source
 960     /// and destination may overlap.
 961     ///
 962     /// NOTE: this has the *opposite* argument order of [`ptr::copy`].
 963     ///
 964     /// See [`ptr::copy`] for safety concerns and examples.
 965     ///
 966     /// [`ptr::copy`]: crate::ptr::copy()
 967     #[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
 968     #[stable(feature = "pointer_methods", since = "1.26.0")]
 969     #[inline]
 970     pub const unsafe fn copy_from(self, src: *const T, count: usize)
 971     where
 972         T: Sized,
 973     {
 974         // SAFETY: the caller must uphold the safety contract for `copy`.
 975         unsafe { copy(src, self, count) }
 976     }
 977
 978     /// Copies `count * size_of<T>` bytes from `src` to `self`. The source
 979     /// and destination may *not* overlap.
 980     ///
 981     /// NOTE: this has the *opposite* argument order of [`ptr::copy_nonoverlapping`].
 982     ///
 983     /// See [`ptr::copy_nonoverlapping`] for safety concerns and examples.
 984     ///
 985     /// [`ptr::copy_nonoverlapping`]: crate::ptr::copy_nonoverlapping()
 986     #[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
 987     #[stable(feature = "pointer_methods", since = "1.26.0")]
 988     #[inline]
 989     pub const unsafe fn copy_from_nonoverlapping(self, src: *const T, count: usize)
 990     where
 991         T: Sized,
 992     {
 993         // SAFETY: the caller must uphold the safety contract for `copy_nonoverlapping`.
 994         unsafe { copy_nonoverlapping(src, self, count) }
 995     }
 996
 997     /// Executes the destructor (if any) of the pointed-to value.
 998     ///
 999     /// See [`ptr::drop_in_place`] for safety concerns and examples.
1000     ///
1001     /// [`ptr::drop_in_place`]: crate::ptr::drop_in_place()
1002     #[stable(feature = "pointer_methods", since = "1.26.0")]
1003     #[inline]
1004     pub unsafe fn drop_in_place(self) {
1005         // SAFETY: the caller must uphold the safety contract for `drop_in_place`.
1006         unsafe { drop_in_place(self) }
1007     }
1008
1009     /// Overwrites a memory location with the given value without reading or
1010     /// dropping the old value.
1011     ///
1012     /// See [`ptr::write`] for safety concerns and examples.
1013     ///
1014     /// [`ptr::write`]: crate::ptr::write()
1015     #[stable(feature = "pointer_methods", since = "1.26.0")]
1016     #[inline]
1017     pub unsafe fn write(self, val: T)
1018     where
1019         T: Sized,
1020     {
1021         // SAFETY: the caller must uphold the safety contract for `write`.
1022         unsafe { write(self, val) }
1023     }
1024
1025     /// Invokes memset on the specified pointer, setting `count * size_of::<T>()`
1026     /// bytes of memory starting at `self` to `val`.
1027     ///
1028     /// See [`ptr::write_bytes`] for safety concerns and examples.
1029     ///
1030     /// [`ptr::write_bytes`]: crate::ptr::write_bytes()
1031     #[stable(feature = "pointer_methods", since = "1.26.0")]
1032     #[inline]
1033     pub unsafe fn write_bytes(self, val: u8, count: usize)
1034     where
1035         T: Sized,
1036     {
1037         // SAFETY: the caller must uphold the safety contract for `write_bytes`.
1038         unsafe { write_bytes(self, val, count) }
1039     }
1040
1041     /// Performs a volatile write of a memory location with the given value without
1042     /// reading or dropping the old value.
1043     ///
1044     /// Volatile operations are intended to act on I/O memory, and are guaranteed
1045     /// to not be elided or reordered by the compiler across other volatile
1046     /// operations.
1047     ///
1048     /// See [`ptr::write_volatile`] for safety concerns and examples.
1049     ///
1050     /// [`ptr::write_volatile`]: crate::ptr::write_volatile()
1051     #[stable(feature = "pointer_methods", since = "1.26.0")]
1052     #[inline]
1053     pub unsafe fn write_volatile(self, val: T)
1054     where
1055         T: Sized,
1056     {
1057         // SAFETY: the caller must uphold the safety contract for `write_volatile`.
1058         unsafe { write_volatile(self, val) }
1059     }
1060
1061     /// Overwrites a memory location with the given value without reading or
1062     /// dropping the old value.
1063     ///
1064     /// Unlike `write`, the pointer may be unaligned.
1065     ///
1066     /// See [`ptr::write_unaligned`] for safety concerns and examples.
1067     ///
1068     /// [`ptr::write_unaligned`]: crate::ptr::write_unaligned()
1069     #[stable(feature = "pointer_methods", since = "1.26.0")]
1070     #[rustc_const_unstable(feature = "const_ptr_write", issue = "none")]
1071     #[inline]
1072     pub const unsafe fn write_unaligned(self, val: T)
1073     where
1074         T: Sized,
1075     {
1076         // SAFETY: the caller must uphold the safety contract for `write_unaligned`.
1077         unsafe { write_unaligned(self, val) }
1078     }
1079
1080     /// Replaces the value at `self` with `src`, returning the old
1081     /// value, without dropping either.
1082     ///
1083     /// See [`ptr::replace`] for safety concerns and examples.
1084     ///
1085     /// [`ptr::replace`]: crate::ptr::replace()
1086     #[stable(feature = "pointer_methods", since = "1.26.0")]
1087     #[inline]
1088     pub unsafe fn replace(self, src: T) -> T
1089     where
1090         T: Sized,
1091     {
1092         // SAFETY: the caller must uphold the safety contract for `replace`.
1093         unsafe { replace(self, src) }
1094     }
1095
1096     /// Swaps the values at two mutable locations of the same type, without
1097     /// deinitializing either. They may overlap, unlike `mem::swap` which is
1098     /// otherwise equivalent.
1099     ///
1100     /// See [`ptr::swap`] for safety concerns and examples.
1101     ///
1102     /// [`ptr::swap`]: crate::ptr::swap()
1103     #[stable(feature = "pointer_methods", since = "1.26.0")]
1104     #[inline]
1105     pub unsafe fn swap(self, with: *mut T)
1106     where
1107         T: Sized,
1108     {
1109         // SAFETY: the caller must uphold the safety contract for `swap`.
1110         unsafe { swap(self, with) }
1111     }
1112
1113     /// Computes the offset that needs to be applied to the pointer in order to make it aligned to
1114     /// `align`.
1115     ///
1116     /// If it is not possible to align the pointer, the implementation returns
1117     /// `usize::MAX`. It is permissible for the implementation to *always*
1118     /// return `usize::MAX`. Only your algorithm's performance can depend
1119     /// on getting a usable offset here, not its correctness.
1120     ///
1121     /// The offset is expressed in number of `T` elements, and not bytes. The value returned can be
1122     /// used with the `wrapping_add` method.
1123     ///
1124     /// There are no guarantees whatsoever that offsetting the pointer will not overflow or go
1125     /// beyond the allocation that the pointer points into. It is up to the caller to ensure that
1126     /// the returned offset is correct in all terms other than alignment.
1127     ///
1128     /// # Panics
1129     ///
1130     /// The function panics if `align` is not a power-of-two.
1131     ///
1132     /// # Examples
1133     ///
1134     /// Accessing adjacent `u8` as `u16`
1135     ///
1136     /// ```
1137     /// # fn foo(n: usize) {
1138     /// # use std::mem::align_of;
1139     /// # unsafe {
1140     /// let x = [5u8, 6u8, 7u8, 8u8, 9u8];
1141     /// let ptr = x.as_ptr().add(n) as *const u8;
1142     /// let offset = ptr.align_offset(align_of::<u16>());
1143     /// if offset < x.len() - n - 1 {
1144     ///     let u16_ptr = ptr.add(offset) as *const u16;
1145     ///     assert_ne!(*u16_ptr, 500);
1146     /// } else {
1147     ///     // while the pointer can be aligned via `offset`, it would point
1148     ///     // outside the allocation
1149     /// }
1150     /// # } }
1151     /// ```
1152     #[stable(feature = "align_offset", since = "1.36.0")]
1153     pub fn align_offset(self, align: usize) -> usize
1154     where
1155         T: Sized,
1156     {
1157         if !align.is_power_of_two() {
1158             panic!("align_offset: align is not a power-of-two");
1159         }
1160         // SAFETY: `align` has been checked to be a power of 2 above
1161         unsafe { align_offset(self, align) }
1162     }
1163 }
1164
1165 #[lang = "mut_slice_ptr"]
1166 impl<T> *mut [T] {
1167     /// Returns the length of a raw slice.
1168     ///
1169     /// The returned value is the number of **elements**, not the number of bytes.
1170     ///
1171     /// This function is safe, even when the raw slice cannot be cast to a slice
1172     /// reference because the pointer is null or unaligned.
1173     ///
1174     /// # Examples
1175     ///
1176     /// ```rust
1177     /// #![feature(slice_ptr_len)]
1178     /// use std::ptr;
1179     ///
1180     /// let slice: *mut [i8] = ptr::slice_from_raw_parts_mut(ptr::null_mut(), 3);
1181     /// assert_eq!(slice.len(), 3);
1182     /// ```
1183     #[inline]
1184     #[unstable(feature = "slice_ptr_len", issue = "71146")]
1185     #[rustc_const_unstable(feature = "const_slice_ptr_len", issue = "71146")]
1186     pub const fn len(self) -> usize {
1187         #[cfg(bootstrap)]
1188         {
1189             // SAFETY: this is safe because `*const [T]` and `FatPtr<T>` have the same layout.
1190             // Only `std` can make this guarantee.
1191             unsafe { Repr { rust_mut: self }.raw }.len
1192         }
1193         #[cfg(not(bootstrap))]
1194         metadata(self)
1195     }
1196
1197     /// Returns a raw pointer to the slice's buffer.
1198     ///
1199     /// This is equivalent to casting `self` to `*mut T`, but more type-safe.
1200     ///
1201     /// # Examples
1202     ///
1203     /// ```rust
1204     /// #![feature(slice_ptr_get)]
1205     /// use std::ptr;
1206     ///
1207     /// let slice: *mut [i8] = ptr::slice_from_raw_parts_mut(ptr::null_mut(), 3);
1208     /// assert_eq!(slice.as_mut_ptr(), 0 as *mut i8);
1209     /// ```
1210     #[inline]
1211     #[unstable(feature = "slice_ptr_get", issue = "74265")]
1212     #[rustc_const_unstable(feature = "slice_ptr_get", issue = "74265")]
1213     pub const fn as_mut_ptr(self) -> *mut T {
1214         self as *mut T
1215     }
1216
1217     /// Returns a raw pointer to an element or subslice, without doing bounds
1218     /// checking.
1219     ///
1220     /// Calling this method with an out-of-bounds index or when `self` is not dereferencable
1221     /// is *[undefined behavior]* even if the resulting pointer is not used.
1222     ///
1223     /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1224     ///
1225     /// # Examples
1226     ///
1227     /// ```
1228     /// #![feature(slice_ptr_get)]
1229     ///
1230     /// let x = &mut [1, 2, 4] as *mut [i32];
1231     ///
1232     /// unsafe {
1233     ///     assert_eq!(x.get_unchecked_mut(1), x.as_mut_ptr().add(1));
1234     /// }
1235     /// ```
1236     #[unstable(feature = "slice_ptr_get", issue = "74265")]
1237     #[inline]
1238     pub unsafe fn get_unchecked_mut<I>(self, index: I) -> *mut I::Output
1239     where
1240         I: SliceIndex<[T]>,
1241     {
1242         // SAFETY: the caller ensures that `self` is dereferencable and `index` in-bounds.
1243         unsafe { index.get_unchecked_mut(self) }
1244     }
1245
1246     /// Returns `None` if the pointer is null, or else returns a shared slice to
1247     /// the value wrapped in `Some`. In contrast to [`as_ref`], this does not require
1248     /// that the value has to be initialized.
1249     ///
1250     /// For the mutable counterpart see [`as_uninit_slice_mut`].
1251     ///
1252     /// [`as_ref`]: #method.as_ref-1
1253     /// [`as_uninit_slice_mut`]: #method.as_uninit_slice_mut
1254     ///
1255     /// # Safety
1256     ///
1257     /// When calling this method, you have to ensure that *either* the pointer is NULL *or*
1258     /// all of the following is true:
1259     ///
1260     /// * The pointer must be [valid] for reads for `ptr.len() * mem::size_of::<T>()` many bytes,
1261     ///   and it must be properly aligned. This means in particular:
1262     ///
1263     ///     * The entire memory range of this slice must be contained within a single allocated object!
1264     ///       Slices can never span across multiple allocated objects.
1265     ///
1266     ///     * The pointer must be aligned even for zero-length slices. One
1267     ///       reason for this is that enum layout optimizations may rely on references
1268     ///       (including slices of any length) being aligned and non-null to distinguish
1269     ///       them from other data. You can obtain a pointer that is usable as `data`
1270     ///       for zero-length slices using [`NonNull::dangling()`].
1271     ///
1272     /// * The total size `ptr.len() * mem::size_of::<T>()` of the slice must be no larger than `isize::MAX`.
1273     ///   See the safety documentation of [`pointer::offset`].
1274     ///
1275     /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
1276     ///   arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
1277     ///   In particular, for the duration of this lifetime, the memory the pointer points to must
1278     ///   not get mutated (except inside `UnsafeCell`).
1279     ///
1280     /// This applies even if the result of this method is unused!
1281     ///
1282     /// See also [`slice::from_raw_parts`][].
1283     ///
1284     /// [valid]: crate::ptr#safety
1285     #[inline]
1286     #[unstable(feature = "ptr_as_uninit", issue = "75402")]
1287     pub unsafe fn as_uninit_slice<'a>(self) -> Option<&'a [MaybeUninit<T>]> {
1288         if self.is_null() {
1289             None
1290         } else {
1291             // SAFETY: the caller must uphold the safety contract for `as_uninit_slice`.
1292             Some(unsafe { slice::from_raw_parts(self as *const MaybeUninit<T>, self.len()) })
1293         }
1294     }
1295
1296     /// Returns `None` if the pointer is null, or else returns a unique slice to
1297     /// the value wrapped in `Some`. In contrast to [`as_mut`], this does not require
1298     /// that the value has to be initialized.
1299     ///
1300     /// For the shared counterpart see [`as_uninit_slice`].
1301     ///
1302     /// [`as_mut`]: #method.as_mut
1303     /// [`as_uninit_slice`]: #method.as_uninit_slice-1
1304     ///
1305     /// # Safety
1306     ///
1307     /// When calling this method, you have to ensure that *either* the pointer is NULL *or*
1308     /// all of the following is true:
1309     ///
1310     /// * The pointer must be [valid] for reads and writes for `ptr.len() * mem::size_of::<T>()`
1311     ///   many bytes, and it must be properly aligned. This means in particular:
1312     ///
1313     ///     * The entire memory range of this slice must be contained within a single allocated object!
1314     ///       Slices can never span across multiple allocated objects.
1315     ///
1316     ///     * The pointer must be aligned even for zero-length slices. One
1317     ///       reason for this is that enum layout optimizations may rely on references
1318     ///       (including slices of any length) being aligned and non-null to distinguish
1319     ///       them from other data. You can obtain a pointer that is usable as `data`
1320     ///       for zero-length slices using [`NonNull::dangling()`].
1321     ///
1322     /// * The total size `ptr.len() * mem::size_of::<T>()` of the slice must be no larger than `isize::MAX`.
1323     ///   See the safety documentation of [`pointer::offset`].
1324     ///
1325     /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
1326     ///   arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
1327     ///   In particular, for the duration of this lifetime, the memory the pointer points to must
1328     ///   not get accessed (read or written) through any other pointer.
1329     ///
1330     /// This applies even if the result of this method is unused!
1331     ///
1332     /// See also [`slice::from_raw_parts_mut`][].
1333     ///
1334     /// [valid]: crate::ptr#safety
1335     #[inline]
1336     #[unstable(feature = "ptr_as_uninit", issue = "75402")]
1337     pub unsafe fn as_uninit_slice_mut<'a>(self) -> Option<&'a mut [MaybeUninit<T>]> {
1338         if self.is_null() {
1339             None
1340         } else {
1341             // SAFETY: the caller must uphold the safety contract for `as_uninit_slice_mut`.
1342             Some(unsafe { slice::from_raw_parts_mut(self as *mut MaybeUninit<T>, self.len()) })
1343         }
1344     }
1345 }
1346
1347 // Equality for pointers
1348 #[stable(feature = "rust1", since = "1.0.0")]
1349 impl<T: ?Sized> PartialEq for *mut T {
1350     #[inline]
1351     fn eq(&self, other: &*mut T) -> bool {
1352         *self == *other
1353     }
1354 }
1355
1356 #[stable(feature = "rust1", since = "1.0.0")]
1357 impl<T: ?Sized> Eq for *mut T {}
1358
1359 #[stable(feature = "rust1", since = "1.0.0")]
1360 impl<T: ?Sized> Ord for *mut T {
1361     #[inline]
1362     fn cmp(&self, other: &*mut T) -> Ordering {
1363         if self < other {
1364             Less
1365         } else if self == other {
1366             Equal
1367         } else {
1368             Greater
1369         }
1370     }
1371 }
1372
1373 #[stable(feature = "rust1", since = "1.0.0")]
1374 impl<T: ?Sized> PartialOrd for *mut T {
1375     #[inline]
1376     fn partial_cmp(&self, other: &*mut T) -> Option<Ordering> {
1377         Some(self.cmp(other))
1378     }
1379
1380     #[inline]
1381     fn lt(&self, other: &*mut T) -> bool {
1382         *self < *other
1383     }
1384
1385     #[inline]
1386     fn le(&self, other: &*mut T) -> bool {
1387         *self <= *other
1388     }
1389
1390     #[inline]
1391     fn gt(&self, other: &*mut T) -> bool {
1392         *self > *other
1393     }
1394
1395     #[inline]
1396     fn ge(&self, other: &*mut T) -> bool {
1397         *self >= *other
1398     }
1399 }