src/libcore/ptr.rs

   1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 // FIXME: talk about offset, copy_memory, copy_nonoverlapping_memory
  12
  13 //! Raw, unsafe pointers, `*const T`, and `*mut T`.
  14 //!
  15 //! *[See also the pointer primitive types](../../std/primitive.pointer.html).*
  16
  17 #![stable(feature = "rust1", since = "1.0.0")]
  18
  19 use clone::Clone;
  20 use intrinsics;
  21 use ops::{CoerceUnsized, Deref};
  22 use fmt;
  23 use hash;
  24 use option::Option::{self, Some, None};
  25 use marker::{Copy, PhantomData, Send, Sized, Sync, Unsize};
  26 use mem;
  27 use nonzero::NonZero;
  28
  29 use cmp::{PartialEq, Eq, Ord, PartialOrd};
  30 use cmp::Ordering::{self, Less, Equal, Greater};
  31
  32 // FIXME #19649: intrinsic docs don't render, so these have no docs :(
  33
  34 #[stable(feature = "rust1", since = "1.0.0")]
  35 pub use intrinsics::copy_nonoverlapping;
  36
  37 #[stable(feature = "rust1", since = "1.0.0")]
  38 pub use intrinsics::copy;
  39
  40 #[stable(feature = "rust1", since = "1.0.0")]
  41 pub use intrinsics::write_bytes;
  42
  43 #[stable(feature = "drop_in_place", since = "1.8.0")]
  44 pub use intrinsics::drop_in_place;
  45
  46 /// Creates a null raw pointer.
  47 ///
  48 /// # Examples
  49 ///
  50 /// ```
  51 /// use std::ptr;
  52 ///
  53 /// let p: *const i32 = ptr::null();
  54 /// assert!(p.is_null());
  55 /// ```
  56 #[inline]
  57 #[stable(feature = "rust1", since = "1.0.0")]
  58 pub const fn null<T>() -> *const T { 0 as *const T }
  59
  60 /// Creates a null mutable raw pointer.
  61 ///
  62 /// # Examples
  63 ///
  64 /// ```
  65 /// use std::ptr;
  66 ///
  67 /// let p: *mut i32 = ptr::null_mut();
  68 /// assert!(p.is_null());
  69 /// ```
  70 #[inline]
  71 #[stable(feature = "rust1", since = "1.0.0")]
  72 pub const fn null_mut<T>() -> *mut T { 0 as *mut T }
  73
  74 /// Swaps the values at two mutable locations of the same type, without
  75 /// deinitializing either. They may overlap, unlike `mem::swap` which is
  76 /// otherwise equivalent.
  77 ///
  78 /// # Safety
  79 ///
  80 /// This is only unsafe because it accepts a raw pointer.
  81 #[inline]
  82 #[stable(feature = "rust1", since = "1.0.0")]
  83 pub unsafe fn swap<T>(x: *mut T, y: *mut T) {
  84     // Give ourselves some scratch space to work with
  85     let mut tmp: T = mem::uninitialized();
  86
  87     // Perform the swap
  88     copy_nonoverlapping(x, &mut tmp, 1);
  89     copy(y, x, 1); // `x` and `y` may overlap
  90     copy_nonoverlapping(&tmp, y, 1);
  91
  92     // y and t now point to the same thing, but we need to completely forget `tmp`
  93     // because it's no longer relevant.
  94     mem::forget(tmp);
  95 }
  96
  97 /// Replaces the value at `dest` with `src`, returning the old
  98 /// value, without dropping either.
  99 ///
 100 /// # Safety
 101 ///
 102 /// This is only unsafe because it accepts a raw pointer.
 103 /// Otherwise, this operation is identical to `mem::replace`.
 104 #[inline]
 105 #[stable(feature = "rust1", since = "1.0.0")]
 106 pub unsafe fn replace<T>(dest: *mut T, mut src: T) -> T {
 107     mem::swap(&mut *dest, &mut src); // cannot overlap
 108     src
 109 }
 110
 111 /// Reads the value from `src` without moving it. This leaves the
 112 /// memory in `src` unchanged.
 113 ///
 114 /// # Safety
 115 ///
 116 /// Beyond accepting a raw pointer, this is unsafe because it semantically
 117 /// moves the value out of `src` without preventing further usage of `src`.
 118 /// If `T` is not `Copy`, then care must be taken to ensure that the value at
 119 /// `src` is not used before the data is overwritten again (e.g. with `write`,
 120 /// `zero_memory`, or `copy_memory`). Note that `*src = foo` counts as a use
 121 /// because it will attempt to drop the value previously at `*src`.
 122 #[inline(always)]
 123 #[stable(feature = "rust1", since = "1.0.0")]
 124 pub unsafe fn read<T>(src: *const T) -> T {
 125     let mut tmp: T = mem::uninitialized();
 126     copy_nonoverlapping(src, &mut tmp, 1);
 127     tmp
 128 }
 129
 130 #[allow(missing_docs)]
 131 #[inline(always)]
 132 #[unstable(feature = "filling_drop",
 133            reason = "may play a larger role in std::ptr future extensions",
 134            issue = "5016")]
 135 pub unsafe fn read_and_drop<T>(dest: *mut T) -> T {
 136     // Copy the data out from `dest`:
 137     let tmp = read(&*dest);
 138
 139     // Now mark `dest` as dropped:
 140     write_bytes(dest, mem::POST_DROP_U8, 1);
 141
 142     tmp
 143 }
 144
 145 /// Overwrites a memory location with the given value without reading or
 146 /// dropping the old value.
 147 ///
 148 /// # Safety
 149 ///
 150 /// This operation is marked unsafe because it accepts a raw pointer.
 151 ///
 152 /// It does not drop the contents of `dst`. This is safe, but it could leak
 153 /// allocations or resources, so care must be taken not to overwrite an object
 154 /// that should be dropped.
 155 ///
 156 /// This is appropriate for initializing uninitialized memory, or overwriting
 157 /// memory that has previously been `read` from.
 158 #[inline]
 159 #[stable(feature = "rust1", since = "1.0.0")]
 160 pub unsafe fn write<T>(dst: *mut T, src: T) {
 161     intrinsics::move_val_init(&mut *dst, src)
 162 }
 163
 164 /// Performs a volatile read of the value from `src` without moving it. This
 165 /// leaves the memory in `src` unchanged.
 166 ///
 167 /// Volatile operations are intended to act on I/O memory, and are guaranteed
 168 /// to not be elided or reordered by the compiler across other volatile
 169 /// operations.
 170 ///
 171 /// # Notes
 172 ///
 173 /// Rust does not currently have a rigorously and formally defined memory model,
 174 /// so the precise semantics of what "volatile" means here is subject to change
 175 /// over time. That being said, the semantics will almost always end up pretty
 176 /// similar to [C11's definition of volatile][c11].
 177 ///
 178 /// [c11]: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf
 179 ///
 180 /// # Safety
 181 ///
 182 /// Beyond accepting a raw pointer, this is unsafe because it semantically
 183 /// moves the value out of `src` without preventing further usage of `src`.
 184 /// If `T` is not `Copy`, then care must be taken to ensure that the value at
 185 /// `src` is not used before the data is overwritten again (e.g. with `write`,
 186 /// `zero_memory`, or `copy_memory`). Note that `*src = foo` counts as a use
 187 /// because it will attempt to drop the value previously at `*src`.
 188 #[inline]
 189 #[stable(feature = "volatile", since = "1.9.0")]
 190 pub unsafe fn read_volatile<T>(src: *const T) -> T {
 191     intrinsics::volatile_load(src)
 192 }
 193
 194 /// Performs a volatile write of a memory location with the given value without
 195 /// reading or dropping the old value.
 196 ///
 197 /// Volatile operations are intended to act on I/O memory, and are guaranteed
 198 /// to not be elided or reordered by the compiler across other volatile
 199 /// operations.
 200 ///
 201 /// # Notes
 202 ///
 203 /// Rust does not currently have a rigorously and formally defined memory model,
 204 /// so the precise semantics of what "volatile" means here is subject to change
 205 /// over time. That being said, the semantics will almost always end up pretty
 206 /// similar to [C11's definition of volatile][c11].
 207 ///
 208 /// [c11]: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf
 209 ///
 210 /// # Safety
 211 ///
 212 /// This operation is marked unsafe because it accepts a raw pointer.
 213 ///
 214 /// It does not drop the contents of `dst`. This is safe, but it could leak
 215 /// allocations or resources, so care must be taken not to overwrite an object
 216 /// that should be dropped.
 217 ///
 218 /// This is appropriate for initializing uninitialized memory, or overwriting
 219 /// memory that has previously been `read` from.
 220 #[inline]
 221 #[stable(feature = "volatile", since = "1.9.0")]
 222 pub unsafe fn write_volatile<T>(dst: *mut T, src: T) {
 223     intrinsics::volatile_store(dst, src);
 224 }
 225
 226 #[lang = "const_ptr"]
 227 impl<T: ?Sized> *const T {
 228     /// Returns true if the pointer is null.
 229     ///
 230     /// # Examples
 231     ///
 232     /// Basic usage:
 233     ///
 234     /// ```
 235     /// let s: &str = "Follow the rabbit";
 236     /// let ptr: *const u8 = s.as_ptr();
 237     /// assert!(!ptr.is_null());
 238     /// ```
 239     #[stable(feature = "rust1", since = "1.0.0")]
 240     #[inline]
 241     pub fn is_null(self) -> bool where T: Sized {
 242         self == null()
 243     }
 244
 245     /// Returns `None` if the pointer is null, or else returns a reference to
 246     /// the value wrapped in `Some`.
 247     ///
 248     /// # Safety
 249     ///
 250     /// While this method and its mutable counterpart are useful for
 251     /// null-safety, it is important to note that this is still an unsafe
 252     /// operation because the returned value could be pointing to invalid
 253     /// memory.
 254     ///
 255     /// Additionally, the lifetime `'a` returned is arbitrarily chosen and does
 256     /// not necessarily reflect the actual lifetime of the data.
 257     ///
 258     /// # Examples
 259     ///
 260     /// Basic usage:
 261     ///
 262     /// ```ignore
 263     /// let val: *const u8 = &10u8 as *const u8;
 264     ///
 265     /// unsafe {
 266     ///     if let Some(val_back) = val.as_ref() {
 267     ///         println!("We got back the value: {}!", val_back);
 268     ///     }
 269     /// }
 270     /// ```
 271     #[stable(feature = "ptr_as_ref", since = "1.9.0")]
 272     #[inline]
 273     pub unsafe fn as_ref<'a>(self) -> Option<&'a T> where T: Sized {
 274         if self.is_null() {
 275             None
 276         } else {
 277             Some(&*self)
 278         }
 279     }
 280
 281     /// Calculates the offset from a pointer. `count` is in units of T; e.g. a
 282     /// `count` of 3 represents a pointer offset of `3 * sizeof::<T>()` bytes.
 283     ///
 284     /// # Safety
 285     ///
 286     /// Both the starting and resulting pointer must be either in bounds or one
 287     /// byte past the end of an allocated object. If either pointer is out of
 288     /// bounds or arithmetic overflow occurs then
 289     /// any further use of the returned value will result in undefined behavior.
 290     ///
 291     /// # Examples
 292     ///
 293     /// Basic usage:
 294     ///
 295     /// ```
 296     /// let s: &str = "123";
 297     /// let ptr: *const u8 = s.as_ptr();
 298     ///
 299     /// unsafe {
 300     ///     println!("{}", *ptr.offset(1) as char);
 301     ///     println!("{}", *ptr.offset(2) as char);
 302     /// }
 303     /// ```
 304     #[stable(feature = "rust1", since = "1.0.0")]
 305     #[inline]
 306     pub unsafe fn offset(self, count: isize) -> *const T where T: Sized {
 307         intrinsics::offset(self, count)
 308     }
 309 }
 310
 311 #[lang = "mut_ptr"]
 312 impl<T: ?Sized> *mut T {
 313     /// Returns true if the pointer is null.
 314     ///
 315     /// # Examples
 316     ///
 317     /// Basic usage:
 318     ///
 319     /// ```
 320     /// let mut s = [1, 2, 3];
 321     /// let ptr: *mut u32 = s.as_mut_ptr();
 322     /// assert!(!ptr.is_null());
 323     /// ```
 324     #[stable(feature = "rust1", since = "1.0.0")]
 325     #[inline]
 326     pub fn is_null(self) -> bool where T: Sized {
 327         self == null_mut()
 328     }
 329
 330     /// Returns `None` if the pointer is null, or else returns a reference to
 331     /// the value wrapped in `Some`.
 332     ///
 333     /// # Safety
 334     ///
 335     /// While this method and its mutable counterpart are useful for
 336     /// null-safety, it is important to note that this is still an unsafe
 337     /// operation because the returned value could be pointing to invalid
 338     /// memory.
 339     ///
 340     /// Additionally, the lifetime `'a` returned is arbitrarily chosen and does
 341     /// not necessarily reflect the actual lifetime of the data.
 342     ///
 343     /// # Examples
 344     ///
 345     /// Basic usage:
 346     ///
 347     /// ```ignore
 348     /// let val: *mut u8 = &mut 10u8 as *mut u8;
 349     ///
 350     /// unsafe {
 351     ///     if let Some(val_back) = val.as_ref() {
 352     ///         println!("We got back the value: {}!", val_back);
 353     ///     }
 354     /// }
 355     /// ```
 356     #[stable(feature = "ptr_as_ref", since = "1.9.0")]
 357     #[inline]
 358     pub unsafe fn as_ref<'a>(self) -> Option<&'a T> where T: Sized {
 359         if self.is_null() {
 360             None
 361         } else {
 362             Some(&*self)
 363         }
 364     }
 365
 366     /// Calculates the offset from a pointer. `count` is in units of T; e.g. a
 367     /// `count` of 3 represents a pointer offset of `3 * sizeof::<T>()` bytes.
 368     ///
 369     /// # Safety
 370     ///
 371     /// The offset must be in-bounds of the object, or one-byte-past-the-end.
 372     /// Otherwise `offset` invokes Undefined Behavior, regardless of whether
 373     /// the pointer is used.
 374     ///
 375     /// # Examples
 376     ///
 377     /// Basic usage:
 378     ///
 379     /// ```
 380     /// let mut s = [1, 2, 3];
 381     /// let ptr: *mut u32 = s.as_mut_ptr();
 382     ///
 383     /// unsafe {
 384     ///     println!("{}", *ptr.offset(1));
 385     ///     println!("{}", *ptr.offset(2));
 386     /// }
 387     /// ```
 388     #[stable(feature = "rust1", since = "1.0.0")]
 389     #[inline]
 390     pub unsafe fn offset(self, count: isize) -> *mut T where T: Sized {
 391         intrinsics::offset(self, count) as *mut T
 392     }
 393
 394     /// Returns `None` if the pointer is null, or else returns a mutable
 395     /// reference to the value wrapped in `Some`.
 396     ///
 397     /// # Safety
 398     ///
 399     /// As with `as_ref`, this is unsafe because it cannot verify the validity
 400     /// of the returned pointer, nor can it ensure that the lifetime `'a`
 401     /// returned is indeed a valid lifetime for the contained data.
 402     ///
 403     /// # Examples
 404     ///
 405     /// Basic usage:
 406     ///
 407     /// ```
 408     /// let mut s = [1, 2, 3];
 409     /// let ptr: *mut u32 = s.as_mut_ptr();
 410     /// ```
 411     #[stable(feature = "ptr_as_ref", since = "1.9.0")]
 412     #[inline]
 413     pub unsafe fn as_mut<'a>(self) -> Option<&'a mut T> where T: Sized {
 414         if self.is_null() {
 415             None
 416         } else {
 417             Some(&mut *self)
 418         }
 419     }
 420 }
 421
 422 // Equality for pointers
 423 #[stable(feature = "rust1", since = "1.0.0")]
 424 impl<T: ?Sized> PartialEq for *const T {
 425     #[inline]
 426     fn eq(&self, other: &*const T) -> bool { *self == *other }
 427 }
 428
 429 #[stable(feature = "rust1", since = "1.0.0")]
 430 impl<T: ?Sized> Eq for *const T {}
 431
 432 #[stable(feature = "rust1", since = "1.0.0")]
 433 impl<T: ?Sized> PartialEq for *mut T {
 434     #[inline]
 435     fn eq(&self, other: &*mut T) -> bool { *self == *other }
 436 }
 437
 438 #[stable(feature = "rust1", since = "1.0.0")]
 439 impl<T: ?Sized> Eq for *mut T {}
 440
 441 #[stable(feature = "rust1", since = "1.0.0")]
 442 impl<T: ?Sized> Clone for *const T {
 443     #[inline]
 444     fn clone(&self) -> *const T {
 445         *self
 446     }
 447 }
 448
 449 #[stable(feature = "rust1", since = "1.0.0")]
 450 impl<T: ?Sized> Clone for *mut T {
 451     #[inline]
 452     fn clone(&self) -> *mut T {
 453         *self
 454     }
 455 }
 456
 457 // Impls for function pointers
 458 macro_rules! fnptr_impls_safety_abi {
 459     ($FnTy: ty, $($Arg: ident),*) => {
 460         #[stable(feature = "rust1", since = "1.0.0")]
 461         impl<Ret, $($Arg),*> Clone for $FnTy {
 462             #[inline]
 463             fn clone(&self) -> Self {
 464                 *self
 465             }
 466         }
 467
 468         #[stable(feature = "fnptr_impls", since = "1.4.0")]
 469         impl<Ret, $($Arg),*> PartialEq for $FnTy {
 470             #[inline]
 471             fn eq(&self, other: &Self) -> bool {
 472                 *self as usize == *other as usize
 473             }
 474         }
 475
 476         #[stable(feature = "fnptr_impls", since = "1.4.0")]
 477         impl<Ret, $($Arg),*> Eq for $FnTy {}
 478
 479         #[stable(feature = "fnptr_impls", since = "1.4.0")]
 480         impl<Ret, $($Arg),*> PartialOrd for $FnTy {
 481             #[inline]
 482             fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
 483                 (*self as usize).partial_cmp(&(*other as usize))
 484             }
 485         }
 486
 487         #[stable(feature = "fnptr_impls", since = "1.4.0")]
 488         impl<Ret, $($Arg),*> Ord for $FnTy {
 489             #[inline]
 490             fn cmp(&self, other: &Self) -> Ordering {
 491                 (*self as usize).cmp(&(*other as usize))
 492             }
 493         }
 494
 495         #[stable(feature = "fnptr_impls", since = "1.4.0")]
 496         impl<Ret, $($Arg),*> hash::Hash for $FnTy {
 497             fn hash<HH: hash::Hasher>(&self, state: &mut HH) {
 498                 state.write_usize(*self as usize)
 499             }
 500         }
 501
 502         #[stable(feature = "fnptr_impls", since = "1.4.0")]
 503         impl<Ret, $($Arg),*> fmt::Pointer for $FnTy {
 504             fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 505                 fmt::Pointer::fmt(&(*self as *const ()), f)
 506             }
 507         }
 508
 509         #[stable(feature = "fnptr_impls", since = "1.4.0")]
 510         impl<Ret, $($Arg),*> fmt::Debug for $FnTy {
 511             fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 512                 fmt::Pointer::fmt(&(*self as *const ()), f)
 513             }
 514         }
 515     }
 516 }
 517
 518 macro_rules! fnptr_impls_args {
 519     ($($Arg: ident),*) => {
 520         fnptr_impls_safety_abi! { extern "Rust" fn($($Arg),*) -> Ret, $($Arg),* }
 521         fnptr_impls_safety_abi! { extern "C" fn($($Arg),*) -> Ret, $($Arg),* }
 522         fnptr_impls_safety_abi! { unsafe extern "Rust" fn($($Arg),*) -> Ret, $($Arg),* }
 523         fnptr_impls_safety_abi! { unsafe extern "C" fn($($Arg),*) -> Ret, $($Arg),* }
 524     }
 525 }
 526
 527 fnptr_impls_args! { }
 528 fnptr_impls_args! { A }
 529 fnptr_impls_args! { A, B }
 530 fnptr_impls_args! { A, B, C }
 531 fnptr_impls_args! { A, B, C, D }
 532 fnptr_impls_args! { A, B, C, D, E }
 533 fnptr_impls_args! { A, B, C, D, E, F }
 534 fnptr_impls_args! { A, B, C, D, E, F, G }
 535 fnptr_impls_args! { A, B, C, D, E, F, G, H }
 536 fnptr_impls_args! { A, B, C, D, E, F, G, H, I }
 537 fnptr_impls_args! { A, B, C, D, E, F, G, H, I, J }
 538 fnptr_impls_args! { A, B, C, D, E, F, G, H, I, J, K }
 539 fnptr_impls_args! { A, B, C, D, E, F, G, H, I, J, K, L }
 540
 541 // Comparison for pointers
 542 #[stable(feature = "rust1", since = "1.0.0")]
 543 impl<T: ?Sized> Ord for *const T {
 544     #[inline]
 545     fn cmp(&self, other: &*const T) -> Ordering {
 546         if self < other {
 547             Less
 548         } else if self == other {
 549             Equal
 550         } else {
 551             Greater
 552         }
 553     }
 554 }
 555
 556 #[stable(feature = "rust1", since = "1.0.0")]
 557 impl<T: ?Sized> PartialOrd for *const T {
 558     #[inline]
 559     fn partial_cmp(&self, other: &*const T) -> Option<Ordering> {
 560         Some(self.cmp(other))
 561     }
 562
 563     #[inline]
 564     fn lt(&self, other: &*const T) -> bool { *self < *other }
 565
 566     #[inline]
 567     fn le(&self, other: &*const T) -> bool { *self <= *other }
 568
 569     #[inline]
 570     fn gt(&self, other: &*const T) -> bool { *self > *other }
 571
 572     #[inline]
 573     fn ge(&self, other: &*const T) -> bool { *self >= *other }
 574 }
 575
 576 #[stable(feature = "rust1", since = "1.0.0")]
 577 impl<T: ?Sized> Ord for *mut T {
 578     #[inline]
 579     fn cmp(&self, other: &*mut T) -> Ordering {
 580         if self < other {
 581             Less
 582         } else if self == other {
 583             Equal
 584         } else {
 585             Greater
 586         }
 587     }
 588 }
 589
 590 #[stable(feature = "rust1", since = "1.0.0")]
 591 impl<T: ?Sized> PartialOrd for *mut T {
 592     #[inline]
 593     fn partial_cmp(&self, other: &*mut T) -> Option<Ordering> {
 594         Some(self.cmp(other))
 595     }
 596
 597     #[inline]
 598     fn lt(&self, other: &*mut T) -> bool { *self < *other }
 599
 600     #[inline]
 601     fn le(&self, other: &*mut T) -> bool { *self <= *other }
 602
 603     #[inline]
 604     fn gt(&self, other: &*mut T) -> bool { *self > *other }
 605
 606     #[inline]
 607     fn ge(&self, other: &*mut T) -> bool { *self >= *other }
 608 }
 609
 610 /// A wrapper around a raw non-null `*mut T` that indicates that the possessor
 611 /// of this wrapper owns the referent. This in turn implies that the
 612 /// `Unique<T>` is `Send`/`Sync` if `T` is `Send`/`Sync`, unlike a raw
 613 /// `*mut T` (which conveys no particular ownership semantics).  It
 614 /// also implies that the referent of the pointer should not be
 615 /// modified without a unique path to the `Unique` reference. Useful
 616 /// for building abstractions like `Vec<T>` or `Box<T>`, which
 617 /// internally use raw pointers to manage the memory that they own.
 618 #[allow(missing_debug_implementations)]
 619 #[unstable(feature = "unique", reason = "needs an RFC to flesh out design",
 620            issue = "27730")]
 621 pub struct Unique<T: ?Sized> {
 622     pointer: NonZero<*const T>,
 623     // NOTE: this marker has no consequences for variance, but is necessary
 624     // for dropck to understand that we logically own a `T`.
 625     //
 626     // For details, see:
 627     // https://github.com/rust-lang/rfcs/blob/master/text/0769-sound-generic-drop.md#phantom-data
 628     _marker: PhantomData<T>,
 629 }
 630
 631 /// `Unique` pointers are `Send` if `T` is `Send` because the data they
 632 /// reference is unaliased. Note that this aliasing invariant is
 633 /// unenforced by the type system; the abstraction using the
 634 /// `Unique` must enforce it.
 635 #[unstable(feature = "unique", issue = "27730")]
 636 unsafe impl<T: Send + ?Sized> Send for Unique<T> { }
 637
 638 /// `Unique` pointers are `Sync` if `T` is `Sync` because the data they
 639 /// reference is unaliased. Note that this aliasing invariant is
 640 /// unenforced by the type system; the abstraction using the
 641 /// `Unique` must enforce it.
 642 #[unstable(feature = "unique", issue = "27730")]
 643 unsafe impl<T: Sync + ?Sized> Sync for Unique<T> { }
 644
 645 #[unstable(feature = "unique", issue = "27730")]
 646 impl<T: ?Sized> Unique<T> {
 647     /// Creates a new `Unique`.
 648     ///
 649     /// # Safety
 650     ///
 651     /// `ptr` must be non-null.
 652     pub const unsafe fn new(ptr: *mut T) -> Unique<T> {
 653         Unique { pointer: NonZero::new(ptr), _marker: PhantomData }
 654     }
 655
 656     /// Dereferences the content.
 657     pub unsafe fn get(&self) -> &T {
 658         &**self.pointer
 659     }
 660
 661     /// Mutably dereferences the content.
 662     pub unsafe fn get_mut(&mut self) -> &mut T {
 663         &mut ***self
 664     }
 665 }
 666
 667 #[unstable(feature = "unique", issue = "27730")]
 668 impl<T: ?Sized, U: ?Sized> CoerceUnsized<Unique<U>> for Unique<T> where T: Unsize<U> { }
 669
 670 #[unstable(feature = "unique", issue= "27730")]
 671 impl<T:?Sized> Deref for Unique<T> {
 672     type Target = *mut T;
 673
 674     #[inline]
 675     fn deref(&self) -> &*mut T {
 676         unsafe { mem::transmute(&*self.pointer) }
 677     }
 678 }
 679
 680 #[stable(feature = "rust1", since = "1.0.0")]
 681 impl<T> fmt::Pointer for Unique<T> {
 682     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 683         fmt::Pointer::fmt(&*self.pointer, f)
 684     }
 685 }
 686
 687 /// A wrapper around a raw non-null `*mut T` that indicates that the possessor
 688 /// of this wrapper has shared ownership of the referent. Useful for
 689 /// building abstractions like `Rc<T>` or `Arc<T>`, which internally
 690 /// use raw pointers to manage the memory that they own.
 691 #[allow(missing_debug_implementations)]
 692 #[unstable(feature = "shared", reason = "needs an RFC to flesh out design",
 693            issue = "27730")]
 694 pub struct Shared<T: ?Sized> {
 695     pointer: NonZero<*const T>,
 696     // NOTE: this marker has no consequences for variance, but is necessary
 697     // for dropck to understand that we logically own a `T`.
 698     //
 699     // For details, see:
 700     // https://github.com/rust-lang/rfcs/blob/master/text/0769-sound-generic-drop.md#phantom-data
 701     _marker: PhantomData<T>,
 702 }
 703
 704 /// `Shared` pointers are not `Send` because the data they reference may be aliased.
 705 // NB: This impl is unnecessary, but should provide better error messages.
 706 #[unstable(feature = "shared", issue = "27730")]
 707 impl<T: ?Sized> !Send for Shared<T> { }
 708
 709 /// `Shared` pointers are not `Sync` because the data they reference may be aliased.
 710 // NB: This impl is unnecessary, but should provide better error messages.
 711 #[unstable(feature = "shared", issue = "27730")]
 712 impl<T: ?Sized> !Sync for Shared<T> { }
 713
 714 #[unstable(feature = "shared", issue = "27730")]
 715 impl<T: ?Sized> Shared<T> {
 716     /// Creates a new `Shared`.
 717     ///
 718     /// # Safety
 719     ///
 720     /// `ptr` must be non-null.
 721     pub unsafe fn new(ptr: *mut T) -> Self {
 722         Shared { pointer: NonZero::new(ptr), _marker: PhantomData }
 723     }
 724 }
 725
 726 #[unstable(feature = "shared", issue = "27730")]
 727 impl<T: ?Sized> Clone for Shared<T> {
 728     fn clone(&self) -> Self {
 729         *self
 730     }
 731 }
 732
 733 #[unstable(feature = "shared", issue = "27730")]
 734 impl<T: ?Sized> Copy for Shared<T> { }
 735
 736 #[unstable(feature = "shared", issue = "27730")]
 737 impl<T: ?Sized, U: ?Sized> CoerceUnsized<Shared<U>> for Shared<T> where T: Unsize<U> { }
 738
 739 #[unstable(feature = "shared", issue = "27730")]
 740 impl<T: ?Sized> Deref for Shared<T> {
 741     type Target = *mut T;
 742
 743     #[inline]
 744     fn deref(&self) -> &*mut T {
 745         unsafe { mem::transmute(&*self.pointer) }
 746     }
 747 }
 748
 749 #[unstable(feature = "shared", issue = "27730")]
 750 impl<T> fmt::Pointer for Shared<T> {
 751     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 752         fmt::Pointer::fmt(&*self.pointer, f)
 753     }
 754 }