src/liballoc/boxed.rs

   1 // Copyright 2012-2015 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 //! A pointer type for heap allocation.
  12 //!
  13 //! `Box<T>`, casually referred to as a 'box', provides the simplest form of
  14 //! heap allocation in Rust. Boxes provide ownership for this allocation, and
  15 //! drop their contents when they go out of scope.
  16 //!
  17 //! # Examples
  18 //!
  19 //! Creating a box:
  20 //!
  21 //! ```
  22 //! let x = Box::new(5);
  23 //! ```
  24 //!
  25 //! Creating a recursive data structure:
  26 //!
  27 //! ```
  28 //! #[derive(Debug)]
  29 //! enum List<T> {
  30 //!     Cons(T, Box<List<T>>),
  31 //!     Nil,
  32 //! }
  33 //!
  34 //! fn main() {
  35 //!     let list: List<i32> = List::Cons(1, Box::new(List::Cons(2, Box::new(List::Nil))));
  36 //!     println!("{:?}", list);
  37 //! }
  38 //! ```
  39 //!
  40 //! This will print `Cons(1, Cons(2, Nil))`.
  41 //!
  42 //! Recursive structures must be boxed, because if the definition of `Cons`
  43 //! looked like this:
  44 //!
  45 //! ```compile_fail,E0072
  46 //! # enum List<T> {
  47 //! Cons(T, List<T>),
  48 //! # }
  49 //! ```
  50 //!
  51 //! It wouldn't work. This is because the size of a `List` depends on how many
  52 //! elements are in the list, and so we don't know how much memory to allocate
  53 //! for a `Cons`. By introducing a `Box`, which has a defined size, we know how
  54 //! big `Cons` needs to be.
  55
  56 #![stable(feature = "rust1", since = "1.0.0")]
  57
  58 use core::any::Any;
  59 use core::borrow;
  60 use core::cmp::Ordering;
  61 use core::fmt;
  62 use core::future::Future;
  63 use core::hash::{Hash, Hasher};
  64 use core::iter::FusedIterator;
  65 use core::marker::{Unpin, Unsize};
  66 use core::mem::{self, PinMut};
  67 use core::ops::{CoerceUnsized, Deref, DerefMut, Generator, GeneratorState};
  68 use core::ptr::{self, NonNull, Unique};
  69 use core::task::{Context, Poll, UnsafeTask, TaskObj};
  70 use core::convert::From;
  71
  72 use raw_vec::RawVec;
  73 use str::from_boxed_utf8_unchecked;
  74
  75 /// A pointer type for heap allocation.
  76 ///
  77 /// See the [module-level documentation](../../std/boxed/index.html) for more.
  78 #[lang = "owned_box"]
  79 #[fundamental]
  80 #[stable(feature = "rust1", since = "1.0.0")]
  81 pub struct Box<T: ?Sized>(Unique<T>);
  82
  83 impl<T> Box<T> {
  84     /// Allocates memory on the heap and then places `x` into it.
  85     ///
  86     /// This doesn't actually allocate if `T` is zero-sized.
  87     ///
  88     /// # Examples
  89     ///
  90     /// ```
  91     /// let five = Box::new(5);
  92     /// ```
  93     #[stable(feature = "rust1", since = "1.0.0")]
  94     #[inline(always)]
  95     pub fn new(x: T) -> Box<T> {
  96         box x
  97     }
  98 }
  99
 100 impl<T: ?Sized> Box<T> {
 101     /// Constructs a box from a raw pointer.
 102     ///
 103     /// After calling this function, the raw pointer is owned by the
 104     /// resulting `Box`. Specifically, the `Box` destructor will call
 105     /// the destructor of `T` and free the allocated memory. Since the
 106     /// way `Box` allocates and releases memory is unspecified, the
 107     /// only valid pointer to pass to this function is the one taken
 108     /// from another `Box` via the [`Box::into_raw`] function.
 109     ///
 110     /// This function is unsafe because improper use may lead to
 111     /// memory problems. For example, a double-free may occur if the
 112     /// function is called twice on the same raw pointer.
 113     ///
 114     /// [`Box::into_raw`]: struct.Box.html#method.into_raw
 115     ///
 116     /// # Examples
 117     ///
 118     /// ```
 119     /// let x = Box::new(5);
 120     /// let ptr = Box::into_raw(x);
 121     /// let x = unsafe { Box::from_raw(ptr) };
 122     /// ```
 123     #[stable(feature = "box_raw", since = "1.4.0")]
 124     #[inline]
 125     pub unsafe fn from_raw(raw: *mut T) -> Self {
 126         Box(Unique::new_unchecked(raw))
 127     }
 128
 129     /// Consumes the `Box`, returning the wrapped raw pointer.
 130     ///
 131     /// After calling this function, the caller is responsible for the
 132     /// memory previously managed by the `Box`. In particular, the
 133     /// caller should properly destroy `T` and release the memory. The
 134     /// proper way to do so is to convert the raw pointer back into a
 135     /// `Box` with the [`Box::from_raw`] function.
 136     ///
 137     /// Note: this is an associated function, which means that you have
 138     /// to call it as `Box::into_raw(b)` instead of `b.into_raw()`. This
 139     /// is so that there is no conflict with a method on the inner type.
 140     ///
 141     /// [`Box::from_raw`]: struct.Box.html#method.from_raw
 142     ///
 143     /// # Examples
 144     ///
 145     /// ```
 146     /// let x = Box::new(5);
 147     /// let ptr = Box::into_raw(x);
 148     /// ```
 149     #[stable(feature = "box_raw", since = "1.4.0")]
 150     #[inline]
 151     pub fn into_raw(b: Box<T>) -> *mut T {
 152         Box::into_raw_non_null(b).as_ptr()
 153     }
 154
 155     /// Consumes the `Box`, returning the wrapped pointer as `NonNull<T>`.
 156     ///
 157     /// After calling this function, the caller is responsible for the
 158     /// memory previously managed by the `Box`. In particular, the
 159     /// caller should properly destroy `T` and release the memory. The
 160     /// proper way to do so is to convert the `NonNull<T>` pointer
 161     /// into a raw pointer and back into a `Box` with the [`Box::from_raw`]
 162     /// function.
 163     ///
 164     /// Note: this is an associated function, which means that you have
 165     /// to call it as `Box::into_raw_non_null(b)`
 166     /// instead of `b.into_raw_non_null()`. This
 167     /// is so that there is no conflict with a method on the inner type.
 168     ///
 169     /// [`Box::from_raw`]: struct.Box.html#method.from_raw
 170     ///
 171     /// # Examples
 172     ///
 173     /// ```
 174     /// #![feature(box_into_raw_non_null)]
 175     ///
 176     /// fn main() {
 177     ///     let x = Box::new(5);
 178     ///     let ptr = Box::into_raw_non_null(x);
 179     /// }
 180     /// ```
 181     #[unstable(feature = "box_into_raw_non_null", issue = "47336")]
 182     #[inline]
 183     pub fn into_raw_non_null(b: Box<T>) -> NonNull<T> {
 184         Box::into_unique(b).into()
 185     }
 186
 187     #[unstable(feature = "ptr_internals", issue = "0", reason = "use into_raw_non_null instead")]
 188     #[inline]
 189     #[doc(hidden)]
 190     pub fn into_unique(b: Box<T>) -> Unique<T> {
 191         let unique = b.0;
 192         mem::forget(b);
 193         unique
 194     }
 195
 196     /// Consumes and leaks the `Box`, returning a mutable reference,
 197     /// `&'a mut T`. Here, the lifetime `'a` may be chosen to be `'static`.
 198     ///
 199     /// This function is mainly useful for data that lives for the remainder of
 200     /// the program's life. Dropping the returned reference will cause a memory
 201     /// leak. If this is not acceptable, the reference should first be wrapped
 202     /// with the [`Box::from_raw`] function producing a `Box`. This `Box` can
 203     /// then be dropped which will properly destroy `T` and release the
 204     /// allocated memory.
 205     ///
 206     /// Note: this is an associated function, which means that you have
 207     /// to call it as `Box::leak(b)` instead of `b.leak()`. This
 208     /// is so that there is no conflict with a method on the inner type.
 209     ///
 210     /// [`Box::from_raw`]: struct.Box.html#method.from_raw
 211     ///
 212     /// # Examples
 213     ///
 214     /// Simple usage:
 215     ///
 216     /// ```
 217     /// fn main() {
 218     ///     let x = Box::new(41);
 219     ///     let static_ref: &'static mut usize = Box::leak(x);
 220     ///     *static_ref += 1;
 221     ///     assert_eq!(*static_ref, 42);
 222     /// }
 223     /// ```
 224     ///
 225     /// Unsized data:
 226     ///
 227     /// ```
 228     /// fn main() {
 229     ///     let x = vec![1, 2, 3].into_boxed_slice();
 230     ///     let static_ref = Box::leak(x);
 231     ///     static_ref[0] = 4;
 232     ///     assert_eq!(*static_ref, [4, 2, 3]);
 233     /// }
 234     /// ```
 235     #[stable(feature = "box_leak", since = "1.26.0")]
 236     #[inline]
 237     pub fn leak<'a>(b: Box<T>) -> &'a mut T
 238     where
 239         T: 'a // Technically not needed, but kept to be explicit.
 240     {
 241         unsafe { &mut *Box::into_raw(b) }
 242     }
 243 }
 244
 245 #[stable(feature = "rust1", since = "1.0.0")]
 246 unsafe impl<#[may_dangle] T: ?Sized> Drop for Box<T> {
 247     fn drop(&mut self) {
 248         // FIXME: Do nothing, drop is currently performed by compiler.
 249     }
 250 }
 251
 252 #[stable(feature = "rust1", since = "1.0.0")]
 253 impl<T: Default> Default for Box<T> {
 254     /// Creates a `Box<T>`, with the `Default` value for T.
 255     fn default() -> Box<T> {
 256         box Default::default()
 257     }
 258 }
 259
 260 #[stable(feature = "rust1", since = "1.0.0")]
 261 impl<T> Default for Box<[T]> {
 262     fn default() -> Box<[T]> {
 263         Box::<[T; 0]>::new([])
 264     }
 265 }
 266
 267 #[stable(feature = "default_box_extra", since = "1.17.0")]
 268 impl Default for Box<str> {
 269     fn default() -> Box<str> {
 270         unsafe { from_boxed_utf8_unchecked(Default::default()) }
 271     }
 272 }
 273
 274 #[stable(feature = "rust1", since = "1.0.0")]
 275 impl<T: Clone> Clone for Box<T> {
 276     /// Returns a new box with a `clone()` of this box's contents.
 277     ///
 278     /// # Examples
 279     ///
 280     /// ```
 281     /// let x = Box::new(5);
 282     /// let y = x.clone();
 283     /// ```
 284     #[rustfmt_skip]
 285     #[inline]
 286     fn clone(&self) -> Box<T> {
 287         box { (**self).clone() }
 288     }
 289     /// Copies `source`'s contents into `self` without creating a new allocation.
 290     ///
 291     /// # Examples
 292     ///
 293     /// ```
 294     /// let x = Box::new(5);
 295     /// let mut y = Box::new(10);
 296     ///
 297     /// y.clone_from(&x);
 298     ///
 299     /// assert_eq!(*y, 5);
 300     /// ```
 301     #[inline]
 302     fn clone_from(&mut self, source: &Box<T>) {
 303         (**self).clone_from(&(**source));
 304     }
 305 }
 306
 307
 308 #[stable(feature = "box_slice_clone", since = "1.3.0")]
 309 impl Clone for Box<str> {
 310     fn clone(&self) -> Self {
 311         let len = self.len();
 312         let buf = RawVec::with_capacity(len);
 313         unsafe {
 314             ptr::copy_nonoverlapping(self.as_ptr(), buf.ptr(), len);
 315             from_boxed_utf8_unchecked(buf.into_box())
 316         }
 317     }
 318 }
 319
 320 #[stable(feature = "rust1", since = "1.0.0")]
 321 impl<T: ?Sized + PartialEq> PartialEq for Box<T> {
 322     #[inline]
 323     fn eq(&self, other: &Box<T>) -> bool {
 324         PartialEq::eq(&**self, &**other)
 325     }
 326     #[inline]
 327     fn ne(&self, other: &Box<T>) -> bool {
 328         PartialEq::ne(&**self, &**other)
 329     }
 330 }
 331 #[stable(feature = "rust1", since = "1.0.0")]
 332 impl<T: ?Sized + PartialOrd> PartialOrd for Box<T> {
 333     #[inline]
 334     fn partial_cmp(&self, other: &Box<T>) -> Option<Ordering> {
 335         PartialOrd::partial_cmp(&**self, &**other)
 336     }
 337     #[inline]
 338     fn lt(&self, other: &Box<T>) -> bool {
 339         PartialOrd::lt(&**self, &**other)
 340     }
 341     #[inline]
 342     fn le(&self, other: &Box<T>) -> bool {
 343         PartialOrd::le(&**self, &**other)
 344     }
 345     #[inline]
 346     fn ge(&self, other: &Box<T>) -> bool {
 347         PartialOrd::ge(&**self, &**other)
 348     }
 349     #[inline]
 350     fn gt(&self, other: &Box<T>) -> bool {
 351         PartialOrd::gt(&**self, &**other)
 352     }
 353 }
 354 #[stable(feature = "rust1", since = "1.0.0")]
 355 impl<T: ?Sized + Ord> Ord for Box<T> {
 356     #[inline]
 357     fn cmp(&self, other: &Box<T>) -> Ordering {
 358         Ord::cmp(&**self, &**other)
 359     }
 360 }
 361 #[stable(feature = "rust1", since = "1.0.0")]
 362 impl<T: ?Sized + Eq> Eq for Box<T> {}
 363
 364 #[stable(feature = "rust1", since = "1.0.0")]
 365 impl<T: ?Sized + Hash> Hash for Box<T> {
 366     fn hash<H: Hasher>(&self, state: &mut H) {
 367         (**self).hash(state);
 368     }
 369 }
 370
 371 #[stable(feature = "indirect_hasher_impl", since = "1.22.0")]
 372 impl<T: ?Sized + Hasher> Hasher for Box<T> {
 373     fn finish(&self) -> u64 {
 374         (**self).finish()
 375     }
 376     fn write(&mut self, bytes: &[u8]) {
 377         (**self).write(bytes)
 378     }
 379     fn write_u8(&mut self, i: u8) {
 380         (**self).write_u8(i)
 381     }
 382     fn write_u16(&mut self, i: u16) {
 383         (**self).write_u16(i)
 384     }
 385     fn write_u32(&mut self, i: u32) {
 386         (**self).write_u32(i)
 387     }
 388     fn write_u64(&mut self, i: u64) {
 389         (**self).write_u64(i)
 390     }
 391     fn write_u128(&mut self, i: u128) {
 392         (**self).write_u128(i)
 393     }
 394     fn write_usize(&mut self, i: usize) {
 395         (**self).write_usize(i)
 396     }
 397     fn write_i8(&mut self, i: i8) {
 398         (**self).write_i8(i)
 399     }
 400     fn write_i16(&mut self, i: i16) {
 401         (**self).write_i16(i)
 402     }
 403     fn write_i32(&mut self, i: i32) {
 404         (**self).write_i32(i)
 405     }
 406     fn write_i64(&mut self, i: i64) {
 407         (**self).write_i64(i)
 408     }
 409     fn write_i128(&mut self, i: i128) {
 410         (**self).write_i128(i)
 411     }
 412     fn write_isize(&mut self, i: isize) {
 413         (**self).write_isize(i)
 414     }
 415 }
 416
 417 #[stable(feature = "from_for_ptrs", since = "1.6.0")]
 418 impl<T> From<T> for Box<T> {
 419     fn from(t: T) -> Self {
 420         Box::new(t)
 421     }
 422 }
 423
 424 #[stable(feature = "box_from_slice", since = "1.17.0")]
 425 impl<'a, T: Copy> From<&'a [T]> for Box<[T]> {
 426     fn from(slice: &'a [T]) -> Box<[T]> {
 427         let mut boxed = unsafe { RawVec::with_capacity(slice.len()).into_box() };
 428         boxed.copy_from_slice(slice);
 429         boxed
 430     }
 431 }
 432
 433 #[stable(feature = "box_from_slice", since = "1.17.0")]
 434 impl<'a> From<&'a str> for Box<str> {
 435     #[inline]
 436     fn from(s: &'a str) -> Box<str> {
 437         unsafe { from_boxed_utf8_unchecked(Box::from(s.as_bytes())) }
 438     }
 439 }
 440
 441 #[stable(feature = "boxed_str_conv", since = "1.19.0")]
 442 impl From<Box<str>> for Box<[u8]> {
 443     #[inline]
 444     fn from(s: Box<str>) -> Self {
 445         unsafe { Box::from_raw(Box::into_raw(s) as *mut [u8]) }
 446     }
 447 }
 448
 449 impl Box<Any> {
 450     #[inline]
 451     #[stable(feature = "rust1", since = "1.0.0")]
 452     /// Attempt to downcast the box to a concrete type.
 453     ///
 454     /// # Examples
 455     ///
 456     /// ```
 457     /// use std::any::Any;
 458     ///
 459     /// fn print_if_string(value: Box<Any>) {
 460     ///     if let Ok(string) = value.downcast::<String>() {
 461     ///         println!("String ({}): {}", string.len(), string);
 462     ///     }
 463     /// }
 464     ///
 465     /// fn main() {
 466     ///     let my_string = "Hello World".to_string();
 467     ///     print_if_string(Box::new(my_string));
 468     ///     print_if_string(Box::new(0i8));
 469     /// }
 470     /// ```
 471     pub fn downcast<T: Any>(self) -> Result<Box<T>, Box<Any>> {
 472         if self.is::<T>() {
 473             unsafe {
 474                 let raw: *mut Any = Box::into_raw(self);
 475                 Ok(Box::from_raw(raw as *mut T))
 476             }
 477         } else {
 478             Err(self)
 479         }
 480     }
 481 }
 482
 483 impl Box<Any + Send> {
 484     #[inline]
 485     #[stable(feature = "rust1", since = "1.0.0")]
 486     /// Attempt to downcast the box to a concrete type.
 487     ///
 488     /// # Examples
 489     ///
 490     /// ```
 491     /// use std::any::Any;
 492     ///
 493     /// fn print_if_string(value: Box<Any + Send>) {
 494     ///     if let Ok(string) = value.downcast::<String>() {
 495     ///         println!("String ({}): {}", string.len(), string);
 496     ///     }
 497     /// }
 498     ///
 499     /// fn main() {
 500     ///     let my_string = "Hello World".to_string();
 501     ///     print_if_string(Box::new(my_string));
 502     ///     print_if_string(Box::new(0i8));
 503     /// }
 504     /// ```
 505     pub fn downcast<T: Any>(self) -> Result<Box<T>, Box<Any + Send>> {
 506         <Box<Any>>::downcast(self).map_err(|s| unsafe {
 507             // reapply the Send marker
 508             Box::from_raw(Box::into_raw(s) as *mut (Any + Send))
 509         })
 510     }
 511 }
 512
 513 #[stable(feature = "rust1", since = "1.0.0")]
 514 impl<T: fmt::Display + ?Sized> fmt::Display for Box<T> {
 515     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 516         fmt::Display::fmt(&**self, f)
 517     }
 518 }
 519
 520 #[stable(feature = "rust1", since = "1.0.0")]
 521 impl<T: fmt::Debug + ?Sized> fmt::Debug for Box<T> {
 522     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 523         fmt::Debug::fmt(&**self, f)
 524     }
 525 }
 526
 527 #[stable(feature = "rust1", since = "1.0.0")]
 528 impl<T: ?Sized> fmt::Pointer for Box<T> {
 529     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 530         // It's not possible to extract the inner Uniq directly from the Box,
 531         // instead we cast it to a *const which aliases the Unique
 532         let ptr: *const T = &**self;
 533         fmt::Pointer::fmt(&ptr, f)
 534     }
 535 }
 536
 537 #[stable(feature = "rust1", since = "1.0.0")]
 538 impl<T: ?Sized> Deref for Box<T> {
 539     type Target = T;
 540
 541     fn deref(&self) -> &T {
 542         &**self
 543     }
 544 }
 545
 546 #[stable(feature = "rust1", since = "1.0.0")]
 547 impl<T: ?Sized> DerefMut for Box<T> {
 548     fn deref_mut(&mut self) -> &mut T {
 549         &mut **self
 550     }
 551 }
 552
 553 #[stable(feature = "rust1", since = "1.0.0")]
 554 impl<I: Iterator + ?Sized> Iterator for Box<I> {
 555     type Item = I::Item;
 556     fn next(&mut self) -> Option<I::Item> {
 557         (**self).next()
 558     }
 559     fn size_hint(&self) -> (usize, Option<usize>) {
 560         (**self).size_hint()
 561     }
 562     fn nth(&mut self, n: usize) -> Option<I::Item> {
 563         (**self).nth(n)
 564     }
 565 }
 566 #[stable(feature = "rust1", since = "1.0.0")]
 567 impl<I: DoubleEndedIterator + ?Sized> DoubleEndedIterator for Box<I> {
 568     fn next_back(&mut self) -> Option<I::Item> {
 569         (**self).next_back()
 570     }
 571 }
 572 #[stable(feature = "rust1", since = "1.0.0")]
 573 impl<I: ExactSizeIterator + ?Sized> ExactSizeIterator for Box<I> {
 574     fn len(&self) -> usize {
 575         (**self).len()
 576     }
 577     fn is_empty(&self) -> bool {
 578         (**self).is_empty()
 579     }
 580 }
 581
 582 #[stable(feature = "fused", since = "1.26.0")]
 583 impl<I: FusedIterator + ?Sized> FusedIterator for Box<I> {}
 584
 585
 586 /// `FnBox` is a version of the `FnOnce` intended for use with boxed
 587 /// closure objects. The idea is that where one would normally store a
 588 /// `Box<FnOnce()>` in a data structure, you should use
 589 /// `Box<FnBox()>`. The two traits behave essentially the same, except
 590 /// that a `FnBox` closure can only be called if it is boxed. (Note
 591 /// that `FnBox` may be deprecated in the future if `Box<FnOnce()>`
 592 /// closures become directly usable.)
 593 ///
 594 /// # Examples
 595 ///
 596 /// Here is a snippet of code which creates a hashmap full of boxed
 597 /// once closures and then removes them one by one, calling each
 598 /// closure as it is removed. Note that the type of the closures
 599 /// stored in the map is `Box<FnBox() -> i32>` and not `Box<FnOnce()
 600 /// -> i32>`.
 601 ///
 602 /// ```
 603 /// #![feature(fnbox)]
 604 ///
 605 /// use std::boxed::FnBox;
 606 /// use std::collections::HashMap;
 607 ///
 608 /// fn make_map() -> HashMap<i32, Box<FnBox() -> i32>> {
 609 ///     let mut map: HashMap<i32, Box<FnBox() -> i32>> = HashMap::new();
 610 ///     map.insert(1, Box::new(|| 22));
 611 ///     map.insert(2, Box::new(|| 44));
 612 ///     map
 613 /// }
 614 ///
 615 /// fn main() {
 616 ///     let mut map = make_map();
 617 ///     for i in &[1, 2] {
 618 ///         let f = map.remove(&i).unwrap();
 619 ///         assert_eq!(f(), i * 22);
 620 ///     }
 621 /// }
 622 /// ```
 623 #[rustc_paren_sugar]
 624 #[unstable(feature = "fnbox",
 625            reason = "will be deprecated if and when `Box<FnOnce>` becomes usable", issue = "28796")]
 626 pub trait FnBox<A> {
 627     type Output;
 628
 629     fn call_box(self: Box<Self>, args: A) -> Self::Output;
 630 }
 631
 632 #[unstable(feature = "fnbox",
 633            reason = "will be deprecated if and when `Box<FnOnce>` becomes usable", issue = "28796")]
 634 impl<A, F> FnBox<A> for F
 635     where F: FnOnce<A>
 636 {
 637     type Output = F::Output;
 638
 639     fn call_box(self: Box<F>, args: A) -> F::Output {
 640         self.call_once(args)
 641     }
 642 }
 643
 644 #[unstable(feature = "fnbox",
 645            reason = "will be deprecated if and when `Box<FnOnce>` becomes usable", issue = "28796")]
 646 impl<'a, A, R> FnOnce<A> for Box<FnBox<A, Output = R> + 'a> {
 647     type Output = R;
 648
 649     extern "rust-call" fn call_once(self, args: A) -> R {
 650         self.call_box(args)
 651     }
 652 }
 653
 654 #[unstable(feature = "fnbox",
 655            reason = "will be deprecated if and when `Box<FnOnce>` becomes usable", issue = "28796")]
 656 impl<'a, A, R> FnOnce<A> for Box<FnBox<A, Output = R> + Send + 'a> {
 657     type Output = R;
 658
 659     extern "rust-call" fn call_once(self, args: A) -> R {
 660         self.call_box(args)
 661     }
 662 }
 663
 664 #[unstable(feature = "coerce_unsized", issue = "27732")]
 665 impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Box<U>> for Box<T> {}
 666
 667 #[stable(feature = "box_slice_clone", since = "1.3.0")]
 668 impl<T: Clone> Clone for Box<[T]> {
 669     fn clone(&self) -> Self {
 670         let mut new = BoxBuilder {
 671             data: RawVec::with_capacity(self.len()),
 672             len: 0,
 673         };
 674
 675         let mut target = new.data.ptr();
 676
 677         for item in self.iter() {
 678             unsafe {
 679                 ptr::write(target, item.clone());
 680                 target = target.offset(1);
 681             };
 682
 683             new.len += 1;
 684         }
 685
 686         return unsafe { new.into_box() };
 687
 688         // Helper type for responding to panics correctly.
 689         struct BoxBuilder<T> {
 690             data: RawVec<T>,
 691             len: usize,
 692         }
 693
 694         impl<T> BoxBuilder<T> {
 695             unsafe fn into_box(self) -> Box<[T]> {
 696                 let raw = ptr::read(&self.data);
 697                 mem::forget(self);
 698                 raw.into_box()
 699             }
 700         }
 701
 702         impl<T> Drop for BoxBuilder<T> {
 703             fn drop(&mut self) {
 704                 let mut data = self.data.ptr();
 705                 let max = unsafe { data.offset(self.len as isize) };
 706
 707                 while data != max {
 708                     unsafe {
 709                         ptr::read(data);
 710                         data = data.offset(1);
 711                     }
 712                 }
 713             }
 714         }
 715     }
 716 }
 717
 718 #[stable(feature = "box_borrow", since = "1.1.0")]
 719 impl<T: ?Sized> borrow::Borrow<T> for Box<T> {
 720     fn borrow(&self) -> &T {
 721         &**self
 722     }
 723 }
 724
 725 #[stable(feature = "box_borrow", since = "1.1.0")]
 726 impl<T: ?Sized> borrow::BorrowMut<T> for Box<T> {
 727     fn borrow_mut(&mut self) -> &mut T {
 728         &mut **self
 729     }
 730 }
 731
 732 #[stable(since = "1.5.0", feature = "smart_ptr_as_ref")]
 733 impl<T: ?Sized> AsRef<T> for Box<T> {
 734     fn as_ref(&self) -> &T {
 735         &**self
 736     }
 737 }
 738
 739 #[stable(since = "1.5.0", feature = "smart_ptr_as_ref")]
 740 impl<T: ?Sized> AsMut<T> for Box<T> {
 741     fn as_mut(&mut self) -> &mut T {
 742         &mut **self
 743     }
 744 }
 745
 746 #[unstable(feature = "generator_trait", issue = "43122")]
 747 impl<T> Generator for Box<T>
 748     where T: Generator + ?Sized
 749 {
 750     type Yield = T::Yield;
 751     type Return = T::Return;
 752     unsafe fn resume(&mut self) -> GeneratorState<Self::Yield, Self::Return> {
 753         (**self).resume()
 754     }
 755 }
 756
 757 /// A pinned, heap allocated reference.
 758 #[unstable(feature = "pin", issue = "49150")]
 759 #[fundamental]
 760 #[repr(transparent)]
 761 pub struct PinBox<T: ?Sized> {
 762     inner: Box<T>,
 763 }
 764
 765 #[unstable(feature = "pin", issue = "49150")]
 766 impl<T> PinBox<T> {
 767     /// Allocate memory on the heap, move the data into it and pin it.
 768     #[unstable(feature = "pin", issue = "49150")]
 769     pub fn new(data: T) -> PinBox<T> {
 770         PinBox { inner: Box::new(data) }
 771     }
 772 }
 773
 774 #[unstable(feature = "pin", issue = "49150")]
 775 impl<T: ?Sized> PinBox<T> {
 776     /// Get a pinned reference to the data in this PinBox.
 777     #[inline]
 778     pub fn as_pin_mut<'a>(&'a mut self) -> PinMut<'a, T> {
 779         unsafe { PinMut::new_unchecked(&mut *self.inner) }
 780     }
 781
 782     /// Constructs a `PinBox` from a raw pointer.
 783     ///
 784     /// After calling this function, the raw pointer is owned by the
 785     /// resulting `PinBox`. Specifically, the `PinBox` destructor will call
 786     /// the destructor of `T` and free the allocated memory. Since the
 787     /// way `PinBox` allocates and releases memory is unspecified, the
 788     /// only valid pointer to pass to this function is the one taken
 789     /// from another `PinBox` via the [`PinBox::into_raw`] function.
 790     ///
 791     /// This function is unsafe because improper use may lead to
 792     /// memory problems. For example, a double-free may occur if the
 793     /// function is called twice on the same raw pointer.
 794     ///
 795     /// [`PinBox::into_raw`]: struct.PinBox.html#method.into_raw
 796     ///
 797     /// # Examples
 798     ///
 799     /// ```
 800     /// #![feature(pin)]
 801     /// use std::boxed::PinBox;
 802     /// let x = PinBox::new(5);
 803     /// let ptr = PinBox::into_raw(x);
 804     /// let x = unsafe { PinBox::from_raw(ptr) };
 805     /// ```
 806     #[inline]
 807     pub unsafe fn from_raw(raw: *mut T) -> Self {
 808         PinBox { inner: Box::from_raw(raw) }
 809     }
 810
 811     /// Consumes the `PinBox`, returning the wrapped raw pointer.
 812     ///
 813     /// After calling this function, the caller is responsible for the
 814     /// memory previously managed by the `PinBox`. In particular, the
 815     /// caller should properly destroy `T` and release the memory. The
 816     /// proper way to do so is to convert the raw pointer back into a
 817     /// `PinBox` with the [`PinBox::from_raw`] function.
 818     ///
 819     /// Note: this is an associated function, which means that you have
 820     /// to call it as `PinBox::into_raw(b)` instead of `b.into_raw()`. This
 821     /// is so that there is no conflict with a method on the inner type.
 822     ///
 823     /// [`PinBox::from_raw`]: struct.PinBox.html#method.from_raw
 824     ///
 825     /// # Examples
 826     ///
 827     /// ```
 828     /// #![feature(pin)]
 829     /// use std::boxed::PinBox;
 830     /// let x = PinBox::new(5);
 831     /// let ptr = PinBox::into_raw(x);
 832     /// ```
 833     #[inline]
 834     pub fn into_raw(b: PinBox<T>) -> *mut T {
 835         Box::into_raw(b.inner)
 836     }
 837
 838     /// Get a mutable reference to the data inside this PinBox.
 839     ///
 840     /// This function is unsafe. Users must guarantee that the data is never
 841     /// moved out of this reference.
 842     #[inline]
 843     pub unsafe fn get_mut<'a>(this: &'a mut PinBox<T>) -> &'a mut T {
 844         &mut *this.inner
 845     }
 846
 847     /// Convert this PinBox into an unpinned Box.
 848     ///
 849     /// This function is unsafe. Users must guarantee that the data is never
 850     /// moved out of the box.
 851     #[inline]
 852     pub unsafe fn unpin(this: PinBox<T>) -> Box<T> {
 853         this.inner
 854     }
 855 }
 856
 857 #[unstable(feature = "pin", issue = "49150")]
 858 impl<T: ?Sized> From<Box<T>> for PinBox<T> {
 859     fn from(boxed: Box<T>) -> PinBox<T> {
 860         PinBox { inner: boxed }
 861     }
 862 }
 863
 864 #[unstable(feature = "pin", issue = "49150")]
 865 impl<T: Unpin + ?Sized> From<PinBox<T>> for Box<T> {
 866     fn from(pinned: PinBox<T>) -> Box<T> {
 867         pinned.inner
 868     }
 869 }
 870
 871 #[unstable(feature = "pin", issue = "49150")]
 872 impl<T: ?Sized> Deref for PinBox<T> {
 873     type Target = T;
 874
 875     fn deref(&self) -> &T {
 876         &*self.inner
 877     }
 878 }
 879
 880 #[unstable(feature = "pin", issue = "49150")]
 881 impl<T: Unpin + ?Sized> DerefMut for PinBox<T> {
 882     fn deref_mut(&mut self) -> &mut T {
 883         &mut *self.inner
 884     }
 885 }
 886
 887 #[unstable(feature = "pin", issue = "49150")]
 888 impl<T: fmt::Display + ?Sized> fmt::Display for PinBox<T> {
 889     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 890         fmt::Display::fmt(&*self.inner, f)
 891     }
 892 }
 893
 894 #[unstable(feature = "pin", issue = "49150")]
 895 impl<T: fmt::Debug + ?Sized> fmt::Debug for PinBox<T> {
 896     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 897         fmt::Debug::fmt(&*self.inner, f)
 898     }
 899 }
 900
 901 #[unstable(feature = "pin", issue = "49150")]
 902 impl<T: ?Sized> fmt::Pointer for PinBox<T> {
 903     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 904         // It's not possible to extract the inner Uniq directly from the Box,
 905         // instead we cast it to a *const which aliases the Unique
 906         let ptr: *const T = &*self.inner;
 907         fmt::Pointer::fmt(&ptr, f)
 908     }
 909 }
 910
 911 #[unstable(feature = "pin", issue = "49150")]
 912 impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<PinBox<U>> for PinBox<T> {}
 913
 914 #[unstable(feature = "pin", issue = "49150")]
 915 impl<T: ?Sized> Unpin for PinBox<T> {}
 916
 917 #[unstable(feature = "futures_api", issue = "50547")]
 918 impl<'a, F: ?Sized + Future + Unpin> Future for Box<F> {
 919     type Output = F::Output;
 920
 921     fn poll(mut self: PinMut<Self>, cx: &mut Context) -> Poll<Self::Output> {
 922         PinMut::new(&mut **self).poll(cx)
 923     }
 924 }
 925
 926 #[unstable(feature = "futures_api", issue = "50547")]
 927 impl<'a, F: ?Sized + Future> Future for PinBox<F> {
 928     type Output = F::Output;
 929
 930     fn poll(mut self: PinMut<Self>, cx: &mut Context) -> Poll<Self::Output> {
 931         self.as_pin_mut().poll(cx)
 932     }
 933 }
 934
 935 #[unstable(feature = "futures_api", issue = "50547")]
 936 unsafe impl<F: Future<Output = ()> + Send + 'static> UnsafeTask for PinBox<F> {
 937     fn into_raw(self) -> *mut () {
 938         PinBox::into_raw(self) as *mut ()
 939     }
 940
 941     unsafe fn poll(task: *mut (), cx: &mut Context) -> Poll<()> {
 942         let ptr = task as *mut F;
 943         let pin: PinMut<F> = PinMut::new_unchecked(&mut *ptr);
 944         pin.poll(cx)
 945     }
 946
 947     unsafe fn drop(task: *mut ()) {
 948         drop(PinBox::from_raw(task as *mut F))
 949     }
 950 }
 951
 952 #[unstable(feature = "futures_api", issue = "50547")]
 953 impl<F: Future<Output = ()> + Send + 'static> From<PinBox<F>> for TaskObj {
 954     fn from(boxed: PinBox<F>) -> Self {
 955         TaskObj::new(boxed)
 956     }
 957 }
 958
 959 #[unstable(feature = "futures_api", issue = "50547")]
 960 impl<F: Future<Output = ()> + Send + 'static> From<Box<F>> for TaskObj {
 961     fn from(boxed: Box<F>) -> Self {
 962         TaskObj::new(PinBox::from(boxed))
 963     }
 964 }