1//! The `Box<T>` type for heap allocation.
2//!
3//! [`Box<T>`], casually referred to as a 'box', provides the simplest form of
4//! heap allocation in Rust. Boxes provide ownership for this allocation, and
5//! drop their contents when they go out of scope. Boxes also ensure that they
6//! never allocate more than `isize::MAX` bytes.
7//!
8//! # Examples
9//!
10//! Move a value from the stack to the heap by creating a [`Box`]:
11//!
12//! ```
13//! let val: u8 = 5;
14//! let boxed: Box<u8> = Box::new(val);
15//! ```
16//!
17//! Move a value from a [`Box`] back to the stack by [dereferencing]:
18//!
19//! ```
20//! let boxed: Box<u8> = Box::new(5);
21//! let val: u8 = *boxed;
22//! ```
23//!
24//! Creating a recursive data structure:
25//!
26//! ```
27//! #[derive(Debug)]
28//! enum List<T> {
29//! Cons(T, Box<List<T>>),
30//! Nil,
31//! }
32//!
33//! let list: List<i32> = List::Cons(1, Box::new(List::Cons(2, Box::new(List::Nil))));
34//! println!("{list:?}");
35//! ```
36//!
37//! This will print `Cons(1, Cons(2, Nil))`.
38//!
39//! Recursive structures must be boxed, because if the definition of `Cons`
40//! looked like this:
41//!
42//! ```compile_fail,E0072
43//! # enum List<T> {
44//! Cons(T, List<T>),
45//! # }
46//! ```
47//!
48//! It wouldn't work. This is because the size of a `List` depends on how many
49//! elements are in the list, and so we don't know how much memory to allocate
50//! for a `Cons`. By introducing a [`Box<T>`], which has a defined size, we know how
51//! big `Cons` needs to be.
52//!
53//! # Memory layout
54//!
55//! For non-zero-sized values, a [`Box`] will use the [`Global`] allocator for
56//! its allocation. It is valid to convert both ways between a [`Box`] and a
57//! raw pointer allocated with the [`Global`] allocator, given that the
58//! [`Layout`] used with the allocator is correct for the type. More precisely,
59//! a `value: *mut T` that has been allocated with the [`Global`] allocator
60//! with `Layout::for_value(&*value)` may be converted into a box using
61//! [`Box::<T>::from_raw(value)`]. Conversely, the memory backing a `value: *mut
62//! T` obtained from [`Box::<T>::into_raw`] may be deallocated using the
63//! [`Global`] allocator with [`Layout::for_value(&*value)`].
64//!
65//! For zero-sized values, the `Box` pointer still has to be [valid] for reads
66//! and writes and sufficiently aligned. In particular, casting any aligned
67//! non-zero integer literal to a raw pointer produces a valid pointer, but a
68//! pointer pointing into previously allocated memory that since got freed is
69//! not valid. The recommended way to build a Box to a ZST if `Box::new` cannot
70//! be used is to use [`ptr::NonNull::dangling`].
71//!
72//! So long as `T: Sized`, a `Box<T>` is guaranteed to be represented
73//! as a single pointer and is also ABI-compatible with C pointers
74//! (i.e. the C type `T*`). This means that if you have extern "C"
75//! Rust functions that will be called from C, you can define those
76//! Rust functions using `Box<T>` types, and use `T*` as corresponding
77//! type on the C side. As an example, consider this C header which
78//! declares functions that create and destroy some kind of `Foo`
79//! value:
80//!
81//! ```c
82//! /* C header */
83//!
84//! /* Returns ownership to the caller */
85//! struct Foo* foo_new(void);
86//!
87//! /* Takes ownership from the caller; no-op when invoked with null */
88//! void foo_delete(struct Foo*);
89//! ```
90//!
91//! These two functions might be implemented in Rust as follows. Here, the
92//! `struct Foo*` type from C is translated to `Box<Foo>`, which captures
93//! the ownership constraints. Note also that the nullable argument to
94//! `foo_delete` is represented in Rust as `Option<Box<Foo>>`, since `Box<Foo>`
95//! cannot be null.
96//!
97//! ```
98//! #[repr(C)]
99//! pub struct Foo;
100//!
101//! #[no_mangle]
102//! pub extern "C" fn foo_new() -> Box<Foo> {
103//! Box::new(Foo)
104//! }
105//!
106//! #[no_mangle]
107//! pub extern "C" fn foo_delete(_: Option<Box<Foo>>) {}
108//! ```
109//!
110//! Even though `Box<T>` has the same representation and C ABI as a C pointer,
111//! this does not mean that you can convert an arbitrary `T*` into a `Box<T>`
112//! and expect things to work. `Box<T>` values will always be fully aligned,
113//! non-null pointers. Moreover, the destructor for `Box<T>` will attempt to
114//! free the value with the global allocator. In general, the best practice
115//! is to only use `Box<T>` for pointers that originated from the global
116//! allocator.
117//!
118//! **Important.** At least at present, you should avoid using
119//! `Box<T>` types for functions that are defined in C but invoked
120//! from Rust. In those cases, you should directly mirror the C types
121//! as closely as possible. Using types like `Box<T>` where the C
122//! definition is just using `T*` can lead to undefined behavior, as
123//! described in [rust-lang/unsafe-code-guidelines#198][ucg#198].
124//!
125//! # Considerations for unsafe code
126//!
127//! **Warning: This section is not normative and is subject to change, possibly
128//! being relaxed in the future! It is a simplified summary of the rules
129//! currently implemented in the compiler.**
130//!
131//! The aliasing rules for `Box<T>` are the same as for `&mut T`. `Box<T>`
132//! asserts uniqueness over its content. Using raw pointers derived from a box
133//! after that box has been mutated through, moved or borrowed as `&mut T`
134//! is not allowed. For more guidance on working with box from unsafe code, see
135//! [rust-lang/unsafe-code-guidelines#326][ucg#326].
136//!
137//!
138//! [ucg#198]: https://github.com/rust-lang/unsafe-code-guidelines/issues/198
139//! [ucg#326]: https://github.com/rust-lang/unsafe-code-guidelines/issues/326
140//! [dereferencing]: core::ops::Deref
141//! [`Box::<T>::from_raw(value)`]: Box::from_raw
142//! [`Global`]: crate::alloc::Global
143//! [`Layout`]: crate::alloc::Layout
144//! [`Layout::for_value(&*value)`]: crate::alloc::Layout::for_value
145//! [valid]: ptr#safety
146
147use core::any::Any;
148use core::borrow;
149use core::cmp::Ordering;
150use core::convert::{From, TryFrom};
151
152// use core::error::Error;
153use core::fmt;
154use core::future::Future;
155use core::hash::{Hash, Hasher};
156#[cfg(not(no_global_oom_handling))]
157use core::iter::FromIterator;
158use core::iter::{FusedIterator, Iterator};
159use core::marker::Unpin;
160use core::mem;
161use core::ops::{Deref, DerefMut};
162use core::pin::Pin;
163use core::ptr::{self, NonNull};
164use core::task::{Context, Poll};
165
166use super::alloc::{AllocError, Allocator, Global, Layout};
167use super::raw_vec::RawVec;
168#[cfg(not(no_global_oom_handling))]
169use super::vec::Vec;
170#[cfg(not(no_global_oom_handling))]
171use alloc_crate::alloc::handle_alloc_error;
172
173/// A pointer type for heap allocation.
174///
175/// See the [module-level documentation](../../std/boxed/index.html) for more.
176pub struct Box<T: ?Sized, A: Allocator = Global>(NonNull<T>, A);
177
178// Safety: Box owns both T and A, so sending is safe if
179// sending is safe for T and A.
180unsafe impl<T: ?Sized, A: Allocator> Send for Box<T, A>
181where
182 T: Send,
183 A: Send,
184{
185}
186
187// Safety: Box owns both T and A, so sharing is safe if
188// sharing is safe for T and A.
189unsafe impl<T: ?Sized, A: Allocator> Sync for Box<T, A>
190where
191 T: Sync,
192 A: Sync,
193{
194}
195
196impl<T> Box<T> {
197 /// Allocates memory on the heap and then places `x` into it.
198 ///
199 /// This doesn't actually allocate if `T` is zero-sized.
200 ///
201 /// # Examples
202 ///
203 /// ```
204 /// let five = Box::new(5);
205 /// ```
206 #[cfg(all(not(no_global_oom_handling)))]
207 #[inline(always)]
208 #[must_use]
209 pub fn new(x: T) -> Self {
210 Self::new_in(x, Global)
211 }
212
213 /// Constructs a new box with uninitialized contents.
214 ///
215 /// # Examples
216 ///
217 /// ```
218 /// #![feature(new_uninit)]
219 ///
220 /// let mut five = Box::<u32>::new_uninit();
221 ///
222 /// let five = unsafe {
223 /// // Deferred initialization:
224 /// five.as_mut_ptr().write(5);
225 ///
226 /// five.assume_init()
227 /// };
228 ///
229 /// assert_eq!(*five, 5)
230 /// ```
231 #[cfg(not(no_global_oom_handling))]
232 #[must_use]
233 #[inline(always)]
234 pub fn new_uninit() -> Box<mem::MaybeUninit<T>> {
235 Self::new_uninit_in(Global)
236 }
237
238 /// Constructs a new `Box` with uninitialized contents, with the memory
239 /// being filled with `0` bytes.
240 ///
241 /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage
242 /// of this method.
243 ///
244 /// # Examples
245 ///
246 /// ```
247 /// #![feature(new_uninit)]
248 ///
249 /// let zero = Box::<u32>::new_zeroed();
250 /// let zero = unsafe { zero.assume_init() };
251 ///
252 /// assert_eq!(*zero, 0)
253 /// ```
254 ///
255 /// [zeroed]: mem::MaybeUninit::zeroed
256 #[cfg(not(no_global_oom_handling))]
257 #[must_use]
258 #[inline(always)]
259 pub fn new_zeroed() -> Box<mem::MaybeUninit<T>> {
260 Self::new_zeroed_in(Global)
261 }
262
263 /// Constructs a new `Pin<Box<T>>`. If `T` does not implement [`Unpin`], then
264 /// `x` will be pinned in memory and unable to be moved.
265 ///
266 /// Constructing and pinning of the `Box` can also be done in two steps: `Box::pin(x)`
267 /// does the same as <code>[Box::into_pin]\([Box::new]\(x))</code>. Consider using
268 /// [`into_pin`](Box::into_pin) if you already have a `Box<T>`, or if you want to
269 /// construct a (pinned) `Box` in a different way than with [`Box::new`].
270 #[cfg(not(no_global_oom_handling))]
271 #[must_use]
272 #[inline(always)]
273 pub fn pin(x: T) -> Pin<Box<T>> {
274 Box::new(x).into()
275 }
276
277 /// Allocates memory on the heap then places `x` into it,
278 /// returning an error if the allocation fails
279 ///
280 /// This doesn't actually allocate if `T` is zero-sized.
281 ///
282 /// # Examples
283 ///
284 /// ```
285 /// #![feature(allocator_api)]
286 ///
287 /// let five = Box::try_new(5)?;
288 /// # Ok::<(), std::alloc::AllocError>(())
289 /// ```
290 #[inline(always)]
291 pub fn try_new(x: T) -> Result<Self, AllocError> {
292 Self::try_new_in(x, Global)
293 }
294
295 /// Constructs a new box with uninitialized contents on the heap,
296 /// returning an error if the allocation fails
297 ///
298 /// # Examples
299 ///
300 /// ```
301 /// #![feature(allocator_api, new_uninit)]
302 ///
303 /// let mut five = Box::<u32>::try_new_uninit()?;
304 ///
305 /// let five = unsafe {
306 /// // Deferred initialization:
307 /// five.as_mut_ptr().write(5);
308 ///
309 /// five.assume_init()
310 /// };
311 ///
312 /// assert_eq!(*five, 5);
313 /// # Ok::<(), std::alloc::AllocError>(())
314 /// ```
315 #[inline(always)]
316 pub fn try_new_uninit() -> Result<Box<mem::MaybeUninit<T>>, AllocError> {
317 Box::try_new_uninit_in(Global)
318 }
319
320 /// Constructs a new `Box` with uninitialized contents, with the memory
321 /// being filled with `0` bytes on the heap
322 ///
323 /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage
324 /// of this method.
325 ///
326 /// # Examples
327 ///
328 /// ```
329 /// #![feature(allocator_api, new_uninit)]
330 ///
331 /// let zero = Box::<u32>::try_new_zeroed()?;
332 /// let zero = unsafe { zero.assume_init() };
333 ///
334 /// assert_eq!(*zero, 0);
335 /// # Ok::<(), std::alloc::AllocError>(())
336 /// ```
337 ///
338 /// [zeroed]: mem::MaybeUninit::zeroed
339 #[inline(always)]
340 pub fn try_new_zeroed() -> Result<Box<mem::MaybeUninit<T>>, AllocError> {
341 Box::try_new_zeroed_in(Global)
342 }
343}
344
345impl<T, A: Allocator> Box<T, A> {
346 /// Allocates memory in the given allocator then places `x` into it.
347 ///
348 /// This doesn't actually allocate if `T` is zero-sized.
349 ///
350 /// # Examples
351 ///
352 /// ```
353 /// #![feature(allocator_api)]
354 ///
355 /// use std::alloc::System;
356 ///
357 /// let five = Box::new_in(5, System);
358 /// ```
359 #[cfg(not(no_global_oom_handling))]
360 #[must_use]
361 #[inline(always)]
362 pub fn new_in(x: T, alloc: A) -> Self
363 where
364 A: Allocator,
365 {
366 let mut boxed = Self::new_uninit_in(alloc);
367 unsafe {
368 boxed.as_mut_ptr().write(x);
369 boxed.assume_init()
370 }
371 }
372
373 /// Allocates memory in the given allocator then places `x` into it,
374 /// returning an error if the allocation fails
375 ///
376 /// This doesn't actually allocate if `T` is zero-sized.
377 ///
378 /// # Examples
379 ///
380 /// ```
381 /// #![feature(allocator_api)]
382 ///
383 /// use std::alloc::System;
384 ///
385 /// let five = Box::try_new_in(5, System)?;
386 /// # Ok::<(), std::alloc::AllocError>(())
387 /// ```
388 #[inline(always)]
389 pub fn try_new_in(x: T, alloc: A) -> Result<Self, AllocError>
390 where
391 A: Allocator,
392 {
393 let mut boxed = Self::try_new_uninit_in(alloc)?;
394 unsafe {
395 boxed.as_mut_ptr().write(x);
396 Ok(boxed.assume_init())
397 }
398 }
399
400 /// Constructs a new box with uninitialized contents in the provided allocator.
401 ///
402 /// # Examples
403 ///
404 /// ```
405 /// #![feature(allocator_api, new_uninit)]
406 ///
407 /// use std::alloc::System;
408 ///
409 /// let mut five = Box::<u32, _>::new_uninit_in(System);
410 ///
411 /// let five = unsafe {
412 /// // Deferred initialization:
413 /// five.as_mut_ptr().write(5);
414 ///
415 /// five.assume_init()
416 /// };
417 ///
418 /// assert_eq!(*five, 5)
419 /// ```
420 #[cfg(not(no_global_oom_handling))]
421 #[must_use]
422 // #[unstable(feature = "new_uninit", issue = "63291")]
423 #[inline(always)]
424 pub fn new_uninit_in(alloc: A) -> Box<mem::MaybeUninit<T>, A>
425 where
426 A: Allocator,
427 {
428 let layout = Layout::new::<mem::MaybeUninit<T>>();
429 // NOTE: Prefer match over unwrap_or_else since closure sometimes not inlineable.
430 // That would make code size bigger.
431 match Box::try_new_uninit_in(alloc) {
432 Ok(m) => m,
433 Err(_) => handle_alloc_error(layout),
434 }
435 }
436
437 /// Constructs a new box with uninitialized contents in the provided allocator,
438 /// returning an error if the allocation fails
439 ///
440 /// # Examples
441 ///
442 /// ```
443 /// #![feature(allocator_api, new_uninit)]
444 ///
445 /// use std::alloc::System;
446 ///
447 /// let mut five = Box::<u32, _>::try_new_uninit_in(System)?;
448 ///
449 /// let five = unsafe {
450 /// // Deferred initialization:
451 /// five.as_mut_ptr().write(5);
452 ///
453 /// five.assume_init()
454 /// };
455 ///
456 /// assert_eq!(*five, 5);
457 /// # Ok::<(), std::alloc::AllocError>(())
458 /// ```
459 #[inline(always)]
460 pub fn try_new_uninit_in(alloc: A) -> Result<Box<mem::MaybeUninit<T>, A>, AllocError>
461 where
462 A: Allocator,
463 {
464 let layout = Layout::new::<mem::MaybeUninit<T>>();
465 let ptr = alloc.allocate(layout)?.cast();
466 unsafe { Ok(Box::from_raw_in(ptr.as_ptr(), alloc)) }
467 }
468
469 /// Constructs a new `Box` with uninitialized contents, with the memory
470 /// being filled with `0` bytes in the provided allocator.
471 ///
472 /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage
473 /// of this method.
474 ///
475 /// # Examples
476 ///
477 /// ```
478 /// #![feature(allocator_api, new_uninit)]
479 ///
480 /// use std::alloc::System;
481 ///
482 /// let zero = Box::<u32, _>::new_zeroed_in(System);
483 /// let zero = unsafe { zero.assume_init() };
484 ///
485 /// assert_eq!(*zero, 0)
486 /// ```
487 ///
488 /// [zeroed]: mem::MaybeUninit::zeroed
489 #[cfg(not(no_global_oom_handling))]
490 // #[unstable(feature = "new_uninit", issue = "63291")]
491 #[must_use]
492 #[inline(always)]
493 pub fn new_zeroed_in(alloc: A) -> Box<mem::MaybeUninit<T>, A>
494 where
495 A: Allocator,
496 {
497 let layout = Layout::new::<mem::MaybeUninit<T>>();
498 // NOTE: Prefer match over unwrap_or_else since closure sometimes not inlineable.
499 // That would make code size bigger.
500 match Box::try_new_zeroed_in(alloc) {
501 Ok(m) => m,
502 Err(_) => handle_alloc_error(layout),
503 }
504 }
505
506 /// Constructs a new `Box` with uninitialized contents, with the memory
507 /// being filled with `0` bytes in the provided allocator,
508 /// returning an error if the allocation fails,
509 ///
510 /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage
511 /// of this method.
512 ///
513 /// # Examples
514 ///
515 /// ```
516 /// #![feature(allocator_api, new_uninit)]
517 ///
518 /// use std::alloc::System;
519 ///
520 /// let zero = Box::<u32, _>::try_new_zeroed_in(System)?;
521 /// let zero = unsafe { zero.assume_init() };
522 ///
523 /// assert_eq!(*zero, 0);
524 /// # Ok::<(), std::alloc::AllocError>(())
525 /// ```
526 ///
527 /// [zeroed]: mem::MaybeUninit::zeroed
528 #[inline(always)]
529 pub fn try_new_zeroed_in(alloc: A) -> Result<Box<mem::MaybeUninit<T>, A>, AllocError>
530 where
531 A: Allocator,
532 {
533 let layout = Layout::new::<mem::MaybeUninit<T>>();
534 let ptr = alloc.allocate_zeroed(layout)?.cast();
535 unsafe { Ok(Box::from_raw_in(ptr.as_ptr(), alloc)) }
536 }
537
538 /// Constructs a new `Pin<Box<T, A>>`. If `T` does not implement [`Unpin`], then
539 /// `x` will be pinned in memory and unable to be moved.
540 ///
541 /// Constructing and pinning of the `Box` can also be done in two steps: `Box::pin_in(x, alloc)`
542 /// does the same as <code>[Box::into_pin]\([Box::new_in]\(x, alloc))</code>. Consider using
543 /// [`into_pin`](Box::into_pin) if you already have a `Box<T, A>`, or if you want to
544 /// construct a (pinned) `Box` in a different way than with [`Box::new_in`].
545 #[cfg(not(no_global_oom_handling))]
546 #[must_use]
547 #[inline(always)]
548 pub fn pin_in(x: T, alloc: A) -> Pin<Self>
549 where
550 A: 'static + Allocator,
551 {
552 Self::into_pin(Self::new_in(x, alloc))
553 }
554
555 /// Converts a `Box<T>` into a `Box<[T]>`
556 ///
557 /// This conversion does not allocate on the heap and happens in place.
558 #[inline(always)]
559 pub fn into_boxed_slice(boxed: Self) -> Box<[T], A> {
560 let (raw, alloc) = Box::into_raw_with_allocator(boxed);
561 unsafe { Box::from_raw_in(raw as *mut [T; 1], alloc) }
562 }
563
564 /// Consumes the `Box`, returning the wrapped value.
565 ///
566 /// # Examples
567 ///
568 /// ```
569 /// #![feature(box_into_inner)]
570 ///
571 /// let c = Box::new(5);
572 ///
573 /// assert_eq!(Box::into_inner(c), 5);
574 /// ```
575 #[inline(always)]
576 pub fn into_inner(boxed: Self) -> T {
577 let ptr = boxed.0;
578 let unboxed = unsafe { ptr.as_ptr().read() };
579 unsafe { boxed.1.deallocate(ptr.cast(), Layout::new::<T>()) };
580 unboxed
581 }
582}
583
584impl<T> Box<[T]> {
585 /// Constructs a new boxed slice with uninitialized contents.
586 ///
587 /// # Examples
588 ///
589 /// ```
590 /// #![feature(new_uninit)]
591 ///
592 /// let mut values = Box::<[u32]>::new_uninit_slice(3);
593 ///
594 /// let values = unsafe {
595 /// // Deferred initialization:
596 /// values[0].as_mut_ptr().write(1);
597 /// values[1].as_mut_ptr().write(2);
598 /// values[2].as_mut_ptr().write(3);
599 ///
600 /// values.assume_init()
601 /// };
602 ///
603 /// assert_eq!(*values, [1, 2, 3])
604 /// ```
605 #[cfg(not(no_global_oom_handling))]
606 #[must_use]
607 #[inline(always)]
608 pub fn new_uninit_slice(len: usize) -> Box<[mem::MaybeUninit<T>]> {
609 unsafe { RawVec::with_capacity(len).into_box(len) }
610 }
611
612 /// Constructs a new boxed slice with uninitialized contents, with the memory
613 /// being filled with `0` bytes.
614 ///
615 /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage
616 /// of this method.
617 ///
618 /// # Examples
619 ///
620 /// ```
621 /// #![feature(new_uninit)]
622 ///
623 /// let values = Box::<[u32]>::new_zeroed_slice(3);
624 /// let values = unsafe { values.assume_init() };
625 ///
626 /// assert_eq!(*values, [0, 0, 0])
627 /// ```
628 ///
629 /// [zeroed]: mem::MaybeUninit::zeroed
630 #[cfg(not(no_global_oom_handling))]
631 #[must_use]
632 #[inline(always)]
633 pub fn new_zeroed_slice(len: usize) -> Box<[mem::MaybeUninit<T>]> {
634 unsafe { RawVec::with_capacity_zeroed(len).into_box(len) }
635 }
636
637 /// Constructs a new boxed slice with uninitialized contents. Returns an error if
638 /// the allocation fails
639 ///
640 /// # Examples
641 ///
642 /// ```
643 /// #![feature(allocator_api, new_uninit)]
644 ///
645 /// let mut values = Box::<[u32]>::try_new_uninit_slice(3)?;
646 /// let values = unsafe {
647 /// // Deferred initialization:
648 /// values[0].as_mut_ptr().write(1);
649 /// values[1].as_mut_ptr().write(2);
650 /// values[2].as_mut_ptr().write(3);
651 /// values.assume_init()
652 /// };
653 ///
654 /// assert_eq!(*values, [1, 2, 3]);
655 /// # Ok::<(), std::alloc::AllocError>(())
656 /// ```
657 #[inline(always)]
658 pub fn try_new_uninit_slice(len: usize) -> Result<Box<[mem::MaybeUninit<T>]>, AllocError> {
659 unsafe {
660 let layout = match Layout::array::<mem::MaybeUninit<T>>(len) {
661 Ok(l) => l,
662 Err(_) => return Err(AllocError),
663 };
664 let ptr = Global.allocate(layout)?;
665 Ok(RawVec::from_raw_parts_in(ptr.as_ptr() as *mut _, len, Global).into_box(len))
666 }
667 }
668
669 /// Constructs a new boxed slice with uninitialized contents, with the memory
670 /// being filled with `0` bytes. Returns an error if the allocation fails
671 ///
672 /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage
673 /// of this method.
674 ///
675 /// # Examples
676 ///
677 /// ```
678 /// #![feature(allocator_api, new_uninit)]
679 ///
680 /// let values = Box::<[u32]>::try_new_zeroed_slice(3)?;
681 /// let values = unsafe { values.assume_init() };
682 ///
683 /// assert_eq!(*values, [0, 0, 0]);
684 /// # Ok::<(), std::alloc::AllocError>(())
685 /// ```
686 ///
687 /// [zeroed]: mem::MaybeUninit::zeroed
688 #[inline(always)]
689 pub fn try_new_zeroed_slice(len: usize) -> Result<Box<[mem::MaybeUninit<T>]>, AllocError> {
690 unsafe {
691 let layout = match Layout::array::<mem::MaybeUninit<T>>(len) {
692 Ok(l) => l,
693 Err(_) => return Err(AllocError),
694 };
695 let ptr = Global.allocate_zeroed(layout)?;
696 Ok(RawVec::from_raw_parts_in(ptr.as_ptr() as *mut _, len, Global).into_box(len))
697 }
698 }
699}
700
701impl<T, A: Allocator> Box<[T], A> {
702 /// Constructs a new boxed slice with uninitialized contents in the provided allocator.
703 ///
704 /// # Examples
705 ///
706 /// ```
707 /// #![feature(allocator_api, new_uninit)]
708 ///
709 /// use std::alloc::System;
710 ///
711 /// let mut values = Box::<[u32], _>::new_uninit_slice_in(3, System);
712 ///
713 /// let values = unsafe {
714 /// // Deferred initialization:
715 /// values[0].as_mut_ptr().write(1);
716 /// values[1].as_mut_ptr().write(2);
717 /// values[2].as_mut_ptr().write(3);
718 ///
719 /// values.assume_init()
720 /// };
721 ///
722 /// assert_eq!(*values, [1, 2, 3])
723 /// ```
724 #[cfg(not(no_global_oom_handling))]
725 #[must_use]
726 #[inline(always)]
727 pub fn new_uninit_slice_in(len: usize, alloc: A) -> Box<[mem::MaybeUninit<T>], A> {
728 unsafe { RawVec::with_capacity_in(len, alloc).into_box(len) }
729 }
730
731 /// Constructs a new boxed slice with uninitialized contents in the provided allocator,
732 /// with the memory being filled with `0` bytes.
733 ///
734 /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage
735 /// of this method.
736 ///
737 /// # Examples
738 ///
739 /// ```
740 /// #![feature(allocator_api, new_uninit)]
741 ///
742 /// use std::alloc::System;
743 ///
744 /// let values = Box::<[u32], _>::new_zeroed_slice_in(3, System);
745 /// let values = unsafe { values.assume_init() };
746 ///
747 /// assert_eq!(*values, [0, 0, 0])
748 /// ```
749 ///
750 /// [zeroed]: mem::MaybeUninit::zeroed
751 #[cfg(not(no_global_oom_handling))]
752 #[must_use]
753 #[inline(always)]
754 pub fn new_zeroed_slice_in(len: usize, alloc: A) -> Box<[mem::MaybeUninit<T>], A> {
755 unsafe { RawVec::with_capacity_zeroed_in(len, alloc).into_box(len) }
756 }
757
758 pub fn into_vec(self) -> Vec<T, A>
759 where
760 A: Allocator,
761 {
762 unsafe {
763 let len = self.len();
764 let (b, alloc) = Box::into_raw_with_allocator(self);
765 Vec::from_raw_parts_in(b as *mut T, len, len, alloc)
766 }
767 }
768}
769
770impl<T, A: Allocator> Box<mem::MaybeUninit<T>, A> {
771 /// Converts to `Box<T, A>`.
772 ///
773 /// # Safety
774 ///
775 /// As with [`MaybeUninit::assume_init`],
776 /// it is up to the caller to guarantee that the value
777 /// really is in an initialized state.
778 /// Calling this when the content is not yet fully initialized
779 /// causes immediate undefined behavior.
780 ///
781 /// [`MaybeUninit::assume_init`]: mem::MaybeUninit::assume_init
782 ///
783 /// # Examples
784 ///
785 /// ```
786 /// #![feature(new_uninit)]
787 ///
788 /// let mut five = Box::<u32>::new_uninit();
789 ///
790 /// let five: Box<u32> = unsafe {
791 /// // Deferred initialization:
792 /// five.as_mut_ptr().write(5);
793 ///
794 /// five.assume_init()
795 /// };
796 ///
797 /// assert_eq!(*five, 5)
798 /// ```
799 #[inline(always)]
800 pub unsafe fn assume_init(self) -> Box<T, A> {
801 let (raw, alloc) = Box::into_raw_with_allocator(self);
802 unsafe { Box::from_raw_in(raw as *mut T, alloc) }
803 }
804
805 /// Writes the value and converts to `Box<T, A>`.
806 ///
807 /// This method converts the box similarly to [`Box::assume_init`] but
808 /// writes `value` into it before conversion thus guaranteeing safety.
809 /// In some scenarios use of this method may improve performance because
810 /// the compiler may be able to optimize copying from stack.
811 ///
812 /// # Examples
813 ///
814 /// ```
815 /// #![feature(new_uninit)]
816 ///
817 /// let big_box = Box::<[usize; 1024]>::new_uninit();
818 ///
819 /// let mut array = [0; 1024];
820 /// for (i, place) in array.iter_mut().enumerate() {
821 /// *place = i;
822 /// }
823 ///
824 /// // The optimizer may be able to elide this copy, so previous code writes
825 /// // to heap directly.
826 /// let big_box = Box::write(big_box, array);
827 ///
828 /// for (i, x) in big_box.iter().enumerate() {
829 /// assert_eq!(*x, i);
830 /// }
831 /// ```
832 #[inline(always)]
833 pub fn write(mut boxed: Self, value: T) -> Box<T, A> {
834 unsafe {
835 (*boxed).write(value);
836 boxed.assume_init()
837 }
838 }
839}
840
841impl<T, A: Allocator> Box<[mem::MaybeUninit<T>], A> {
842 /// Converts to `Box<[T], A>`.
843 ///
844 /// # Safety
845 ///
846 /// As with [`MaybeUninit::assume_init`],
847 /// it is up to the caller to guarantee that the values
848 /// really are in an initialized state.
849 /// Calling this when the content is not yet fully initialized
850 /// causes immediate undefined behavior.
851 ///
852 /// [`MaybeUninit::assume_init`]: mem::MaybeUninit::assume_init
853 ///
854 /// # Examples
855 ///
856 /// ```
857 /// #![feature(new_uninit)]
858 ///
859 /// let mut values = Box::<[u32]>::new_uninit_slice(3);
860 ///
861 /// let values = unsafe {
862 /// // Deferred initialization:
863 /// values[0].as_mut_ptr().write(1);
864 /// values[1].as_mut_ptr().write(2);
865 /// values[2].as_mut_ptr().write(3);
866 ///
867 /// values.assume_init()
868 /// };
869 ///
870 /// assert_eq!(*values, [1, 2, 3])
871 /// ```
872 #[inline(always)]
873 pub unsafe fn assume_init(self) -> Box<[T], A> {
874 let (raw, alloc) = Box::into_raw_with_allocator(self);
875 unsafe { Box::from_raw_in(raw as *mut [T], alloc) }
876 }
877}
878
879impl<T: ?Sized> Box<T> {
880 /// Constructs a box from a raw pointer.
881 ///
882 /// After calling this function, the raw pointer is owned by the
883 /// resulting `Box`. Specifically, the `Box` destructor will call
884 /// the destructor of `T` and free the allocated memory. For this
885 /// to be safe, the memory must have been allocated in accordance
886 /// with the [memory layout] used by `Box` .
887 ///
888 /// # Safety
889 ///
890 /// This function is unsafe because improper use may lead to
891 /// memory problems. For example, a double-free may occur if the
892 /// function is called twice on the same raw pointer.
893 ///
894 /// The safety conditions are described in the [memory layout] section.
895 ///
896 /// # Examples
897 ///
898 /// Recreate a `Box` which was previously converted to a raw pointer
899 /// using [`Box::into_raw`]:
900 /// ```
901 /// let x = Box::new(5);
902 /// let ptr = Box::into_raw(x);
903 /// let x = unsafe { Box::from_raw(ptr) };
904 /// ```
905 /// Manually create a `Box` from scratch by using the global allocator:
906 /// ```
907 /// use std::alloc::{alloc, Layout};
908 ///
909 /// unsafe {
910 /// let ptr = alloc(Layout::new::<i32>()) as *mut i32;
911 /// // In general .write is required to avoid attempting to destruct
912 /// // the (uninitialized) previous contents of `ptr`, though for this
913 /// // simple example `*ptr = 5` would have worked as well.
914 /// ptr.write(5);
915 /// let x = Box::from_raw(ptr);
916 /// }
917 /// ```
918 ///
919 /// [memory layout]: self#memory-layout
920 /// [`Layout`]: crate::Layout
921 #[must_use = "call `drop(from_raw(ptr))` if you intend to drop the `Box`"]
922 #[inline(always)]
923 pub unsafe fn from_raw(raw: *mut T) -> Self {
924 unsafe { Self::from_raw_in(raw, Global) }
925 }
926}
927
928impl<T: ?Sized, A: Allocator> Box<T, A> {
929 /// Constructs a box from a raw pointer in the given allocator.
930 ///
931 /// After calling this function, the raw pointer is owned by the
932 /// resulting `Box`. Specifically, the `Box` destructor will call
933 /// the destructor of `T` and free the allocated memory. For this
934 /// to be safe, the memory must have been allocated in accordance
935 /// with the [memory layout] used by `Box` .
936 ///
937 /// # Safety
938 ///
939 /// This function is unsafe because improper use may lead to
940 /// memory problems. For example, a double-free may occur if the
941 /// function is called twice on the same raw pointer.
942 ///
943 ///
944 /// # Examples
945 ///
946 /// Recreate a `Box` which was previously converted to a raw pointer
947 /// using [`Box::into_raw_with_allocator`]:
948 /// ```
949 /// use std::alloc::System;
950 /// # use allocator_api2::boxed::Box;
951 ///
952 /// let x = Box::new_in(5, System);
953 /// let (ptr, alloc) = Box::into_raw_with_allocator(x);
954 /// let x = unsafe { Box::from_raw_in(ptr, alloc) };
955 /// ```
956 /// Manually create a `Box` from scratch by using the system allocator:
957 /// ```
958 /// use allocator_api2::alloc::{Allocator, Layout, System};
959 /// # use allocator_api2::boxed::Box;
960 ///
961 /// unsafe {
962 /// let ptr = System.allocate(Layout::new::<i32>())?.as_ptr().cast::<i32>();
963 /// // In general .write is required to avoid attempting to destruct
964 /// // the (uninitialized) previous contents of `ptr`, though for this
965 /// // simple example `*ptr = 5` would have worked as well.
966 /// ptr.write(5);
967 /// let x = Box::from_raw_in(ptr, System);
968 /// }
969 /// # Ok::<(), allocator_api2::alloc::AllocError>(())
970 /// ```
971 ///
972 /// [memory layout]: self#memory-layout
973 /// [`Layout`]: crate::Layout
974 #[inline(always)]
975 pub const unsafe fn from_raw_in(raw: *mut T, alloc: A) -> Self {
976 Box(unsafe { NonNull::new_unchecked(raw) }, alloc)
977 }
978
979 /// Consumes the `Box`, returning a wrapped raw pointer.
980 ///
981 /// The pointer will be properly aligned and non-null.
982 ///
983 /// After calling this function, the caller is responsible for the
984 /// memory previously managed by the `Box`. In particular, the
985 /// caller should properly destroy `T` and release the memory, taking
986 /// into account the [memory layout] used by `Box`. The easiest way to
987 /// do this is to convert the raw pointer back into a `Box` with the
988 /// [`Box::from_raw`] function, allowing the `Box` destructor to perform
989 /// the cleanup.
990 ///
991 /// Note: this is an associated function, which means that you have
992 /// to call it as `Box::into_raw(b)` instead of `b.into_raw()`. This
993 /// is so that there is no conflict with a method on the inner type.
994 ///
995 /// # Examples
996 /// Converting the raw pointer back into a `Box` with [`Box::from_raw`]
997 /// for automatic cleanup:
998 /// ```
999 /// let x = Box::new(String::from("Hello"));
1000 /// let ptr = Box::into_raw(x);
1001 /// let x = unsafe { Box::from_raw(ptr) };
1002 /// ```
1003 /// Manual cleanup by explicitly running the destructor and deallocating
1004 /// the memory:
1005 /// ```
1006 /// use std::alloc::{dealloc, Layout};
1007 /// use std::ptr;
1008 ///
1009 /// let x = Box::new(String::from("Hello"));
1010 /// let p = Box::into_raw(x);
1011 /// unsafe {
1012 /// ptr::drop_in_place(p);
1013 /// dealloc(p as *mut u8, Layout::new::<String>());
1014 /// }
1015 /// ```
1016 ///
1017 /// [memory layout]: self#memory-layout
1018 #[inline(always)]
1019 pub fn into_raw(b: Self) -> *mut T {
1020 Self::into_raw_with_allocator(b).0
1021 }
1022
1023 /// Consumes the `Box`, returning a wrapped raw pointer and the allocator.
1024 ///
1025 /// The pointer will be properly aligned and non-null.
1026 ///
1027 /// After calling this function, the caller is responsible for the
1028 /// memory previously managed by the `Box`. In particular, the
1029 /// caller should properly destroy `T` and release the memory, taking
1030 /// into account the [memory layout] used by `Box`. The easiest way to
1031 /// do this is to convert the raw pointer back into a `Box` with the
1032 /// [`Box::from_raw_in`] function, allowing the `Box` destructor to perform
1033 /// the cleanup.
1034 ///
1035 /// Note: this is an associated function, which means that you have
1036 /// to call it as `Box::into_raw_with_allocator(b)` instead of `b.into_raw_with_allocator()`. This
1037 /// is so that there is no conflict with a method on the inner type.
1038 ///
1039 /// # Examples
1040 /// Converting the raw pointer back into a `Box` with [`Box::from_raw_in`]
1041 /// for automatic cleanup:
1042 /// ```
1043 /// #![feature(allocator_api)]
1044 ///
1045 /// use std::alloc::System;
1046 ///
1047 /// let x = Box::new_in(String::from("Hello"), System);
1048 /// let (ptr, alloc) = Box::into_raw_with_allocator(x);
1049 /// let x = unsafe { Box::from_raw_in(ptr, alloc) };
1050 /// ```
1051 /// Manual cleanup by explicitly running the destructor and deallocating
1052 /// the memory:
1053 /// ```
1054 /// #![feature(allocator_api)]
1055 ///
1056 /// use std::alloc::{Allocator, Layout, System};
1057 /// use std::ptr::{self, NonNull};
1058 ///
1059 /// let x = Box::new_in(String::from("Hello"), System);
1060 /// let (ptr, alloc) = Box::into_raw_with_allocator(x);
1061 /// unsafe {
1062 /// ptr::drop_in_place(ptr);
1063 /// let non_null = NonNull::new_unchecked(ptr);
1064 /// alloc.deallocate(non_null.cast(), Layout::new::<String>());
1065 /// }
1066 /// ```
1067 ///
1068 /// [memory layout]: self#memory-layout
1069 #[inline(always)]
1070 pub fn into_raw_with_allocator(b: Self) -> (*mut T, A) {
1071 let (leaked, alloc) = Box::into_non_null(b);
1072 (leaked.as_ptr(), alloc)
1073 }
1074
1075 #[inline(always)]
1076 pub fn into_non_null(b: Self) -> (NonNull<T>, A) {
1077 // Box is recognized as a "unique pointer" by Stacked Borrows, but internally it is a
1078 // raw pointer for the type system. Turning it directly into a raw pointer would not be
1079 // recognized as "releasing" the unique pointer to permit aliased raw accesses,
1080 // so all raw pointer methods have to go through `Box::leak`. Turning *that* to a raw pointer
1081 // behaves correctly.
1082 let alloc = unsafe { ptr::read(&b.1) };
1083 (NonNull::from(Box::leak(b)), alloc)
1084 }
1085
1086 /// Returns a reference to the underlying allocator.
1087 ///
1088 /// Note: this is an associated function, which means that you have
1089 /// to call it as `Box::allocator(&b)` instead of `b.allocator()`. This
1090 /// is so that there is no conflict with a method on the inner type.
1091 #[inline(always)]
1092 pub const fn allocator(b: &Self) -> &A {
1093 &b.1
1094 }
1095
1096 /// Consumes and leaks the `Box`, returning a mutable reference,
1097 /// `&'a mut T`. Note that the type `T` must outlive the chosen lifetime
1098 /// `'a`. If the type has only static references, or none at all, then this
1099 /// may be chosen to be `'static`.
1100 ///
1101 /// This function is mainly useful for data that lives for the remainder of
1102 /// the program's life. Dropping the returned reference will cause a memory
1103 /// leak. If this is not acceptable, the reference should first be wrapped
1104 /// with the [`Box::from_raw`] function producing a `Box`. This `Box` can
1105 /// then be dropped which will properly destroy `T` and release the
1106 /// allocated memory.
1107 ///
1108 /// Note: this is an associated function, which means that you have
1109 /// to call it as `Box::leak(b)` instead of `b.leak()`. This
1110 /// is so that there is no conflict with a method on the inner type.
1111 ///
1112 /// # Examples
1113 ///
1114 /// Simple usage:
1115 ///
1116 /// ```
1117 /// let x = Box::new(41);
1118 /// let static_ref: &'static mut usize = Box::leak(x);
1119 /// *static_ref += 1;
1120 /// assert_eq!(*static_ref, 42);
1121 /// ```
1122 ///
1123 /// Unsized data:
1124 ///
1125 /// ```
1126 /// let x = vec![1, 2, 3].into_boxed_slice();
1127 /// let static_ref = Box::leak(x);
1128 /// static_ref[0] = 4;
1129 /// assert_eq!(*static_ref, [4, 2, 3]);
1130 /// ```
1131 #[inline(always)]
1132 fn leak<'a>(b: Self) -> &'a mut T
1133 where
1134 A: 'a,
1135 {
1136 unsafe { &mut *mem::ManuallyDrop::new(b).0.as_ptr() }
1137 }
1138
1139 /// Converts a `Box<T>` into a `Pin<Box<T>>`. If `T` does not implement [`Unpin`], then
1140 /// `*boxed` will be pinned in memory and unable to be moved.
1141 ///
1142 /// This conversion does not allocate on the heap and happens in place.
1143 ///
1144 /// This is also available via [`From`].
1145 ///
1146 /// Constructing and pinning a `Box` with <code>Box::into_pin([Box::new]\(x))</code>
1147 /// can also be written more concisely using <code>[Box::pin]\(x)</code>.
1148 /// This `into_pin` method is useful if you already have a `Box<T>`, or you are
1149 /// constructing a (pinned) `Box` in a different way than with [`Box::new`].
1150 ///
1151 /// # Notes
1152 ///
1153 /// It's not recommended that crates add an impl like `From<Box<T>> for Pin<T>`,
1154 /// as it'll introduce an ambiguity when calling `Pin::from`.
1155 /// A demonstration of such a poor impl is shown below.
1156 ///
1157 /// ```compile_fail
1158 /// # use std::pin::Pin;
1159 /// struct Foo; // A type defined in this crate.
1160 /// impl From<Box<()>> for Pin<Foo> {
1161 /// fn from(_: Box<()>) -> Pin<Foo> {
1162 /// Pin::new(Foo)
1163 /// }
1164 /// }
1165 ///
1166 /// let foo = Box::new(());
1167 /// let bar = Pin::from(foo);
1168 /// ```
1169 #[inline(always)]
1170 pub fn into_pin(boxed: Self) -> Pin<Self>
1171 where
1172 A: 'static,
1173 {
1174 // It's not possible to move or replace the insides of a `Pin<Box<T>>`
1175 // when `T: !Unpin`, so it's safe to pin it directly without any
1176 // additional requirements.
1177 unsafe { Pin::new_unchecked(boxed) }
1178 }
1179}
1180
1181impl<T: ?Sized, A: Allocator> Drop for Box<T, A> {
1182 #[inline(always)]
1183 fn drop(&mut self) {
1184 let layout: Layout = Layout::for_value::<T>(&**self);
1185 unsafe {
1186 ptr::drop_in_place(self.0.as_mut());
1187 self.1.deallocate(self.0.cast(), layout);
1188 }
1189 }
1190}
1191
1192#[cfg(not(no_global_oom_handling))]
1193impl<T: Default> Default for Box<T> {
1194 /// Creates a `Box<T>`, with the `Default` value for T.
1195 #[inline(always)]
1196 fn default() -> Self {
1197 Box::new(T::default())
1198 }
1199}
1200
1201impl<T, A: Allocator + Default> Default for Box<[T], A> {
1202 #[inline(always)]
1203 fn default() -> Self {
1204 let ptr: NonNull<[T]> = NonNull::<[T; 0]>::dangling();
1205 Box(ptr, A::default())
1206 }
1207}
1208
1209impl<A: Allocator + Default> Default for Box<str, A> {
1210 #[inline(always)]
1211 fn default() -> Self {
1212 // SAFETY: This is the same as `Unique::cast<U>` but with an unsized `U = str`.
1213 let ptr: NonNull<str> = unsafe {
1214 let bytes: NonNull<[u8]> = NonNull::<[u8; 0]>::dangling();
1215 NonNull::new_unchecked(bytes.as_ptr() as *mut str)
1216 };
1217 Box(ptr, A::default())
1218 }
1219}
1220
1221#[cfg(not(no_global_oom_handling))]
1222impl<T: Clone, A: Allocator + Clone> Clone for Box<T, A> {
1223 /// Returns a new box with a `clone()` of this box's contents.
1224 ///
1225 /// # Examples
1226 ///
1227 /// ```
1228 /// let x = Box::new(5);
1229 /// let y = x.clone();
1230 ///
1231 /// // The value is the same
1232 /// assert_eq!(x, y);
1233 ///
1234 /// // But they are unique objects
1235 /// assert_ne!(&*x as *const i32, &*y as *const i32);
1236 /// ```
1237 #[inline(always)]
1238 fn clone(&self) -> Self {
1239 // Pre-allocate memory to allow writing the cloned value directly.
1240 let mut boxed = Self::new_uninit_in(self.1.clone());
1241 unsafe {
1242 boxed.write((**self).clone());
1243 boxed.assume_init()
1244 }
1245 }
1246
1247 /// Copies `source`'s contents into `self` without creating a new allocation.
1248 ///
1249 /// # Examples
1250 ///
1251 /// ```
1252 /// let x = Box::new(5);
1253 /// let mut y = Box::new(10);
1254 /// let yp: *const i32 = &*y;
1255 ///
1256 /// y.clone_from(&x);
1257 ///
1258 /// // The value is the same
1259 /// assert_eq!(x, y);
1260 ///
1261 /// // And no allocation occurred
1262 /// assert_eq!(yp, &*y);
1263 /// ```
1264 #[inline(always)]
1265 fn clone_from(&mut self, source: &Self) {
1266 (**self).clone_from(&(**source));
1267 }
1268}
1269
1270#[cfg(not(no_global_oom_handling))]
1271impl Clone for Box<str> {
1272 #[inline(always)]
1273 fn clone(&self) -> Self {
1274 // this makes a copy of the data
1275 let buf: Box<[u8]> = self.as_bytes().into();
1276 unsafe { Box::from_raw(Box::into_raw(buf) as *mut str) }
1277 }
1278}
1279
1280impl<T: ?Sized + PartialEq, A: Allocator> PartialEq for Box<T, A> {
1281 #[inline(always)]
1282 fn eq(&self, other: &Self) -> bool {
1283 PartialEq::eq(&**self, &**other)
1284 }
1285 #[inline(always)]
1286 fn ne(&self, other: &Self) -> bool {
1287 PartialEq::ne(&**self, &**other)
1288 }
1289}
1290
1291impl<T: ?Sized + PartialOrd, A: Allocator> PartialOrd for Box<T, A> {
1292 #[inline(always)]
1293 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
1294 PartialOrd::partial_cmp(&**self, &**other)
1295 }
1296 #[inline(always)]
1297 fn lt(&self, other: &Self) -> bool {
1298 PartialOrd::lt(&**self, &**other)
1299 }
1300 #[inline(always)]
1301 fn le(&self, other: &Self) -> bool {
1302 PartialOrd::le(&**self, &**other)
1303 }
1304 #[inline(always)]
1305 fn ge(&self, other: &Self) -> bool {
1306 PartialOrd::ge(&**self, &**other)
1307 }
1308 #[inline(always)]
1309 fn gt(&self, other: &Self) -> bool {
1310 PartialOrd::gt(&**self, &**other)
1311 }
1312}
1313
1314impl<T: ?Sized + Ord, A: Allocator> Ord for Box<T, A> {
1315 #[inline(always)]
1316 fn cmp(&self, other: &Self) -> Ordering {
1317 Ord::cmp(&**self, &**other)
1318 }
1319}
1320
1321impl<T: ?Sized + Eq, A: Allocator> Eq for Box<T, A> {}
1322
1323impl<T: ?Sized + Hash, A: Allocator> Hash for Box<T, A> {
1324 #[inline(always)]
1325 fn hash<H: Hasher>(&self, state: &mut H) {
1326 (**self).hash(state);
1327 }
1328}
1329
1330impl<T: ?Sized + Hasher, A: Allocator> Hasher for Box<T, A> {
1331 #[inline(always)]
1332 fn finish(&self) -> u64 {
1333 (**self).finish()
1334 }
1335 #[inline(always)]
1336 fn write(&mut self, bytes: &[u8]) {
1337 (**self).write(bytes)
1338 }
1339 #[inline(always)]
1340 fn write_u8(&mut self, i: u8) {
1341 (**self).write_u8(i)
1342 }
1343 #[inline(always)]
1344 fn write_u16(&mut self, i: u16) {
1345 (**self).write_u16(i)
1346 }
1347 #[inline(always)]
1348 fn write_u32(&mut self, i: u32) {
1349 (**self).write_u32(i)
1350 }
1351 #[inline(always)]
1352 fn write_u64(&mut self, i: u64) {
1353 (**self).write_u64(i)
1354 }
1355 #[inline(always)]
1356 fn write_u128(&mut self, i: u128) {
1357 (**self).write_u128(i)
1358 }
1359 #[inline(always)]
1360 fn write_usize(&mut self, i: usize) {
1361 (**self).write_usize(i)
1362 }
1363 #[inline(always)]
1364 fn write_i8(&mut self, i: i8) {
1365 (**self).write_i8(i)
1366 }
1367 #[inline(always)]
1368 fn write_i16(&mut self, i: i16) {
1369 (**self).write_i16(i)
1370 }
1371 #[inline(always)]
1372 fn write_i32(&mut self, i: i32) {
1373 (**self).write_i32(i)
1374 }
1375 #[inline(always)]
1376 fn write_i64(&mut self, i: i64) {
1377 (**self).write_i64(i)
1378 }
1379 #[inline(always)]
1380 fn write_i128(&mut self, i: i128) {
1381 (**self).write_i128(i)
1382 }
1383 #[inline(always)]
1384 fn write_isize(&mut self, i: isize) {
1385 (**self).write_isize(i)
1386 }
1387}
1388
1389#[cfg(not(no_global_oom_handling))]
1390impl<T> From<T> for Box<T> {
1391 /// Converts a `T` into a `Box<T>`
1392 ///
1393 /// The conversion allocates on the heap and moves `t`
1394 /// from the stack into it.
1395 ///
1396 /// # Examples
1397 ///
1398 /// ```rust
1399 /// let x = 5;
1400 /// let boxed = Box::new(5);
1401 ///
1402 /// assert_eq!(Box::from(x), boxed);
1403 /// ```
1404 #[inline(always)]
1405 fn from(t: T) -> Self {
1406 Box::new(t)
1407 }
1408}
1409
1410impl<T: ?Sized, A: Allocator> From<Box<T, A>> for Pin<Box<T, A>>
1411where
1412 A: 'static,
1413{
1414 /// Converts a `Box<T>` into a `Pin<Box<T>>`. If `T` does not implement [`Unpin`], then
1415 /// `*boxed` will be pinned in memory and unable to be moved.
1416 ///
1417 /// This conversion does not allocate on the heap and happens in place.
1418 ///
1419 /// This is also available via [`Box::into_pin`].
1420 ///
1421 /// Constructing and pinning a `Box` with <code><Pin<Box\<T>>>::from([Box::new]\(x))</code>
1422 /// can also be written more concisely using <code>[Box::pin]\(x)</code>.
1423 /// This `From` implementation is useful if you already have a `Box<T>`, or you are
1424 /// constructing a (pinned) `Box` in a different way than with [`Box::new`].
1425 #[inline(always)]
1426 fn from(boxed: Box<T, A>) -> Self {
1427 Box::into_pin(boxed)
1428 }
1429}
1430
1431#[cfg(not(no_global_oom_handling))]
1432impl<T: Copy, A: Allocator + Default> From<&[T]> for Box<[T], A> {
1433 /// Converts a `&[T]` into a `Box<[T]>`
1434 ///
1435 /// This conversion allocates on the heap
1436 /// and performs a copy of `slice` and its contents.
1437 ///
1438 /// # Examples
1439 /// ```rust
1440 /// // create a &[u8] which will be used to create a Box<[u8]>
1441 /// let slice: &[u8] = &[104, 101, 108, 108, 111];
1442 /// let boxed_slice: Box<[u8]> = Box::from(slice);
1443 ///
1444 /// println!("{boxed_slice:?}");
1445 /// ```
1446 #[inline(always)]
1447 fn from(slice: &[T]) -> Box<[T], A> {
1448 let len: usize = slice.len();
1449 let buf: RawVec = RawVec::with_capacity_in(capacity:len, A::default());
1450 unsafe {
1451 ptr::copy_nonoverlapping(src:slice.as_ptr(), dst:buf.ptr(), count:len);
1452 buf.into_box(slice.len()).assume_init()
1453 }
1454 }
1455}
1456
1457#[cfg(not(no_global_oom_handling))]
1458impl<A: Allocator + Default> From<&str> for Box<str, A> {
1459 /// Converts a `&str` into a `Box<str>`
1460 ///
1461 /// This conversion allocates on the heap
1462 /// and performs a copy of `s`.
1463 ///
1464 /// # Examples
1465 ///
1466 /// ```rust
1467 /// let boxed: Box<str> = Box::from("hello");
1468 /// println!("{boxed}");
1469 /// ```
1470 #[inline(always)]
1471 fn from(s: &str) -> Box<str, A> {
1472 let (raw: *mut [u8], alloc: A) = Box::into_raw_with_allocator(Box::<[u8], A>::from(s.as_bytes()));
1473 unsafe { Box::from_raw_in(raw as *mut str, alloc) }
1474 }
1475}
1476
1477impl<A: Allocator> From<Box<str, A>> for Box<[u8], A> {
1478 /// Converts a `Box<str>` into a `Box<[u8]>`
1479 ///
1480 /// This conversion does not allocate on the heap and happens in place.
1481 ///
1482 /// # Examples
1483 /// ```rust
1484 /// // create a Box<str> which will be used to create a Box<[u8]>
1485 /// let boxed: Box<str> = Box::from("hello");
1486 /// let boxed_str: Box<[u8]> = Box::from(boxed);
1487 ///
1488 /// // create a &[u8] which will be used to create a Box<[u8]>
1489 /// let slice: &[u8] = &[104, 101, 108, 108, 111];
1490 /// let boxed_slice = Box::from(slice);
1491 ///
1492 /// assert_eq!(boxed_slice, boxed_str);
1493 /// ```
1494 #[inline(always)]
1495 fn from(s: Box<str, A>) -> Self {
1496 let (raw: *mut str, alloc: A) = Box::into_raw_with_allocator(s);
1497 unsafe { Box::from_raw_in(raw as *mut [u8], alloc) }
1498 }
1499}
1500
1501impl<T, A: Allocator, const N: usize> Box<[T; N], A> {
1502 #[inline(always)]
1503 pub fn slice(b: Self) -> Box<[T], A> {
1504 let (ptr: *mut [T; N], alloc: A) = Box::into_raw_with_allocator(b);
1505 unsafe { Box::from_raw_in(raw:ptr, alloc) }
1506 }
1507
1508 pub fn into_vec(self) -> Vec<T, A>
1509 where
1510 A: Allocator,
1511 {
1512 unsafe {
1513 let (b: *mut [T; N], alloc: A) = Box::into_raw_with_allocator(self);
1514 Vec::from_raw_parts_in(ptr:b as *mut T, N, N, alloc)
1515 }
1516 }
1517}
1518
1519#[cfg(not(no_global_oom_handling))]
1520impl<T, const N: usize> From<[T; N]> for Box<[T]> {
1521 /// Converts a `[T; N]` into a `Box<[T]>`
1522 ///
1523 /// This conversion moves the array to newly heap-allocated memory.
1524 ///
1525 /// # Examples
1526 ///
1527 /// ```rust
1528 /// let boxed: Box<[u8]> = Box::from([4, 2]);
1529 /// println!("{boxed:?}");
1530 /// ```
1531 #[inline(always)]
1532 fn from(array: [T; N]) -> Box<[T]> {
1533 Box::slice(Box::new(array))
1534 }
1535}
1536
1537impl<T, A: Allocator, const N: usize> TryFrom<Box<[T], A>> for Box<[T; N], A> {
1538 type Error = Box<[T], A>;
1539
1540 /// Attempts to convert a `Box<[T]>` into a `Box<[T; N]>`.
1541 ///
1542 /// The conversion occurs in-place and does not require a
1543 /// new memory allocation.
1544 ///
1545 /// # Errors
1546 ///
1547 /// Returns the old `Box<[T]>` in the `Err` variant if
1548 /// `boxed_slice.len()` does not equal `N`.
1549 #[inline(always)]
1550 fn try_from(boxed_slice: Box<[T], A>) -> Result<Self, Self::Error> {
1551 if boxed_slice.len() == N {
1552 let (ptr: *mut [T], alloc: A) = Box::into_raw_with_allocator(boxed_slice);
1553 Ok(unsafe { Box::from_raw_in(raw:ptr as *mut [T; N], alloc) })
1554 } else {
1555 Err(boxed_slice)
1556 }
1557 }
1558}
1559
1560impl<A: Allocator> Box<dyn Any, A> {
1561 /// Attempt to downcast the box to a concrete type.
1562 ///
1563 /// # Examples
1564 ///
1565 /// ```
1566 /// use std::any::Any;
1567 ///
1568 /// fn print_if_string(value: Box<dyn Any>) {
1569 /// if let Ok(string) = value.downcast::<String>() {
1570 /// println!("String ({}): {}", string.len(), string);
1571 /// }
1572 /// }
1573 ///
1574 /// let my_string = "Hello World".to_string();
1575 /// print_if_string(Box::new(my_string));
1576 /// print_if_string(Box::new(0i8));
1577 /// ```
1578 #[inline(always)]
1579 pub fn downcast<T: Any>(self) -> Result<Box<T, A>, Self> {
1580 if self.is::<T>() {
1581 unsafe { Ok(self.downcast_unchecked::<T>()) }
1582 } else {
1583 Err(self)
1584 }
1585 }
1586
1587 /// Downcasts the box to a concrete type.
1588 ///
1589 /// For a safe alternative see [`downcast`].
1590 ///
1591 /// # Examples
1592 ///
1593 /// ```
1594 /// #![feature(downcast_unchecked)]
1595 ///
1596 /// use std::any::Any;
1597 ///
1598 /// let x: Box<dyn Any> = Box::new(1_usize);
1599 ///
1600 /// unsafe {
1601 /// assert_eq!(*x.downcast_unchecked::<usize>(), 1);
1602 /// }
1603 /// ```
1604 ///
1605 /// # Safety
1606 ///
1607 /// The contained value must be of type `T`. Calling this method
1608 /// with the incorrect type is *undefined behavior*.
1609 ///
1610 /// [`downcast`]: Self::downcast
1611 #[inline(always)]
1612 pub unsafe fn downcast_unchecked<T: Any>(self) -> Box<T, A> {
1613 debug_assert!(self.is::<T>());
1614 unsafe {
1615 let (raw, alloc): (*mut dyn Any, _) = Box::into_raw_with_allocator(self);
1616 Box::from_raw_in(raw as *mut T, alloc)
1617 }
1618 }
1619}
1620
1621impl<A: Allocator> Box<dyn Any + Send, A> {
1622 /// Attempt to downcast the box to a concrete type.
1623 ///
1624 /// # Examples
1625 ///
1626 /// ```
1627 /// use std::any::Any;
1628 ///
1629 /// fn print_if_string(value: Box<dyn Any + Send>) {
1630 /// if let Ok(string) = value.downcast::<String>() {
1631 /// println!("String ({}): {}", string.len(), string);
1632 /// }
1633 /// }
1634 ///
1635 /// let my_string = "Hello World".to_string();
1636 /// print_if_string(Box::new(my_string));
1637 /// print_if_string(Box::new(0i8));
1638 /// ```
1639 #[inline(always)]
1640 pub fn downcast<T: Any>(self) -> Result<Box<T, A>, Self> {
1641 if self.is::<T>() {
1642 unsafe { Ok(self.downcast_unchecked::<T>()) }
1643 } else {
1644 Err(self)
1645 }
1646 }
1647
1648 /// Downcasts the box to a concrete type.
1649 ///
1650 /// For a safe alternative see [`downcast`].
1651 ///
1652 /// # Examples
1653 ///
1654 /// ```
1655 /// #![feature(downcast_unchecked)]
1656 ///
1657 /// use std::any::Any;
1658 ///
1659 /// let x: Box<dyn Any + Send> = Box::new(1_usize);
1660 ///
1661 /// unsafe {
1662 /// assert_eq!(*x.downcast_unchecked::<usize>(), 1);
1663 /// }
1664 /// ```
1665 ///
1666 /// # Safety
1667 ///
1668 /// The contained value must be of type `T`. Calling this method
1669 /// with the incorrect type is *undefined behavior*.
1670 ///
1671 /// [`downcast`]: Self::downcast
1672 #[inline(always)]
1673 pub unsafe fn downcast_unchecked<T: Any>(self) -> Box<T, A> {
1674 debug_assert!(self.is::<T>());
1675 unsafe {
1676 let (raw, alloc): (*mut (dyn Any + Send), _) = Box::into_raw_with_allocator(self);
1677 Box::from_raw_in(raw as *mut T, alloc)
1678 }
1679 }
1680}
1681
1682impl<A: Allocator> Box<dyn Any + Send + Sync, A> {
1683 /// Attempt to downcast the box to a concrete type.
1684 ///
1685 /// # Examples
1686 ///
1687 /// ```
1688 /// use std::any::Any;
1689 ///
1690 /// fn print_if_string(value: Box<dyn Any + Send + Sync>) {
1691 /// if let Ok(string) = value.downcast::<String>() {
1692 /// println!("String ({}): {}", string.len(), string);
1693 /// }
1694 /// }
1695 ///
1696 /// let my_string = "Hello World".to_string();
1697 /// print_if_string(Box::new(my_string));
1698 /// print_if_string(Box::new(0i8));
1699 /// ```
1700 #[inline(always)]
1701 pub fn downcast<T: Any>(self) -> Result<Box<T, A>, Self> {
1702 if self.is::<T>() {
1703 unsafe { Ok(self.downcast_unchecked::<T>()) }
1704 } else {
1705 Err(self)
1706 }
1707 }
1708
1709 /// Downcasts the box to a concrete type.
1710 ///
1711 /// For a safe alternative see [`downcast`].
1712 ///
1713 /// # Examples
1714 ///
1715 /// ```
1716 /// #![feature(downcast_unchecked)]
1717 ///
1718 /// use std::any::Any;
1719 ///
1720 /// let x: Box<dyn Any + Send + Sync> = Box::new(1_usize);
1721 ///
1722 /// unsafe {
1723 /// assert_eq!(*x.downcast_unchecked::<usize>(), 1);
1724 /// }
1725 /// ```
1726 ///
1727 /// # Safety
1728 ///
1729 /// The contained value must be of type `T`. Calling this method
1730 /// with the incorrect type is *undefined behavior*.
1731 ///
1732 /// [`downcast`]: Self::downcast
1733 #[inline(always)]
1734 pub unsafe fn downcast_unchecked<T: Any>(self) -> Box<T, A> {
1735 debug_assert!(self.is::<T>());
1736 unsafe {
1737 let (raw, alloc): (*mut (dyn Any + Send + Sync), _) =
1738 Box::into_raw_with_allocator(self);
1739 Box::from_raw_in(raw as *mut T, alloc)
1740 }
1741 }
1742}
1743
1744impl<T: fmt::Display + ?Sized, A: Allocator> fmt::Display for Box<T, A> {
1745 #[inline(always)]
1746 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1747 fmt::Display::fmt(&**self, f)
1748 }
1749}
1750
1751impl<T: fmt::Debug + ?Sized, A: Allocator> fmt::Debug for Box<T, A> {
1752 #[inline(always)]
1753 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1754 fmt::Debug::fmt(&**self, f)
1755 }
1756}
1757
1758impl<T: ?Sized, A: Allocator> fmt::Pointer for Box<T, A> {
1759 #[inline(always)]
1760 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1761 // It's not possible to extract the inner Uniq directly from the Box,
1762 // instead we cast it to a *const which aliases the Unique
1763 let ptr: *const T = &**self;
1764 fmt::Pointer::fmt(&ptr, f)
1765 }
1766}
1767
1768impl<T: ?Sized, A: Allocator> Deref for Box<T, A> {
1769 type Target = T;
1770
1771 #[inline(always)]
1772 fn deref(&self) -> &T {
1773 unsafe { self.0.as_ref() }
1774 }
1775}
1776
1777impl<T: ?Sized, A: Allocator> DerefMut for Box<T, A> {
1778 #[inline(always)]
1779 fn deref_mut(&mut self) -> &mut T {
1780 unsafe { self.0.as_mut() }
1781 }
1782}
1783
1784impl<I: Iterator + ?Sized, A: Allocator> Iterator for Box<I, A> {
1785 type Item = I::Item;
1786
1787 #[inline(always)]
1788 fn next(&mut self) -> Option<I::Item> {
1789 (**self).next()
1790 }
1791
1792 #[inline(always)]
1793 fn size_hint(&self) -> (usize, Option<usize>) {
1794 (**self).size_hint()
1795 }
1796
1797 #[inline(always)]
1798 fn nth(&mut self, n: usize) -> Option<I::Item> {
1799 (**self).nth(n)
1800 }
1801
1802 #[inline(always)]
1803 fn last(self) -> Option<I::Item> {
1804 BoxIter::last(self)
1805 }
1806}
1807
1808trait BoxIter {
1809 type Item;
1810 fn last(self) -> Option<Self::Item>;
1811}
1812
1813impl<I: Iterator + ?Sized, A: Allocator> BoxIter for Box<I, A> {
1814 type Item = I::Item;
1815
1816 #[inline(always)]
1817 fn last(self) -> Option<I::Item> {
1818 #[inline(always)]
1819 fn some<T>(_: Option<T>, x: T) -> Option<T> {
1820 Some(x)
1821 }
1822
1823 self.fold(init:None, f:some)
1824 }
1825}
1826
1827impl<I: DoubleEndedIterator + ?Sized, A: Allocator> DoubleEndedIterator for Box<I, A> {
1828 #[inline(always)]
1829 fn next_back(&mut self) -> Option<I::Item> {
1830 (**self).next_back()
1831 }
1832 #[inline(always)]
1833 fn nth_back(&mut self, n: usize) -> Option<I::Item> {
1834 (**self).nth_back(n)
1835 }
1836}
1837
1838impl<I: ExactSizeIterator + ?Sized, A: Allocator> ExactSizeIterator for Box<I, A> {
1839 #[inline(always)]
1840 fn len(&self) -> usize {
1841 (**self).len()
1842 }
1843}
1844
1845impl<I: FusedIterator + ?Sized, A: Allocator> FusedIterator for Box<I, A> {}
1846
1847#[cfg(not(no_global_oom_handling))]
1848impl<I> FromIterator<I> for Box<[I]> {
1849 #[inline(always)]
1850 fn from_iter<T: IntoIterator<Item = I>>(iter: T) -> Self {
1851 iter.into_iter().collect::<Vec<_>>().into_boxed_slice()
1852 }
1853}
1854
1855#[cfg(not(no_global_oom_handling))]
1856impl<T: Clone, A: Allocator + Clone> Clone for Box<[T], A> {
1857 #[inline(always)]
1858 fn clone(&self) -> Self {
1859 let alloc: A = Box::allocator(self).clone();
1860 let mut vec: Vec = Vec::with_capacity_in(self.len(), alloc);
1861 vec.extend_from_slice(self);
1862 vec.into_boxed_slice()
1863 }
1864
1865 #[inline(always)]
1866 fn clone_from(&mut self, other: &Self) {
1867 if self.len() == other.len() {
1868 self.clone_from_slice(src:other);
1869 } else {
1870 *self = other.clone();
1871 }
1872 }
1873}
1874
1875impl<T: ?Sized, A: Allocator> borrow::Borrow<T> for Box<T, A> {
1876 #[inline(always)]
1877 fn borrow(&self) -> &T {
1878 self
1879 }
1880}
1881
1882impl<T: ?Sized, A: Allocator> borrow::BorrowMut<T> for Box<T, A> {
1883 #[inline(always)]
1884 fn borrow_mut(&mut self) -> &mut T {
1885 self
1886 }
1887}
1888
1889impl<T: ?Sized, A: Allocator> AsRef<T> for Box<T, A> {
1890 #[inline(always)]
1891 fn as_ref(&self) -> &T {
1892 self
1893 }
1894}
1895
1896impl<T: ?Sized, A: Allocator> AsMut<T> for Box<T, A> {
1897 #[inline(always)]
1898 fn as_mut(&mut self) -> &mut T {
1899 self
1900 }
1901}
1902
1903/* Nota bene
1904 *
1905 * We could have chosen not to add this impl, and instead have written a
1906 * function of Pin<Box<T>> to Pin<T>. Such a function would not be sound,
1907 * because Box<T> implements Unpin even when T does not, as a result of
1908 * this impl.
1909 *
1910 * We chose this API instead of the alternative for a few reasons:
1911 * - Logically, it is helpful to understand pinning in regard to the
1912 * memory region being pointed to. For this reason none of the
1913 * standard library pointer types support projecting through a pin
1914 * (Box<T> is the only pointer type in std for which this would be
1915 * safe.)
1916 * - It is in practice very useful to have Box<T> be unconditionally
1917 * Unpin because of trait objects, for which the structural auto
1918 * trait functionality does not apply (e.g., Box<dyn Foo> would
1919 * otherwise not be Unpin).
1920 *
1921 * Another type with the same semantics as Box but only a conditional
1922 * implementation of `Unpin` (where `T: Unpin`) would be valid/safe, and
1923 * could have a method to project a Pin<T> from it.
1924 */
1925impl<T: ?Sized, A: Allocator> Unpin for Box<T, A> where A: 'static {}
1926
1927impl<F: ?Sized + Future + Unpin, A: Allocator> Future for Box<F, A>
1928where
1929 A: 'static,
1930{
1931 type Output = F::Output;
1932
1933 #[inline(always)]
1934 fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
1935 F::poll(self:Pin::new(&mut *self), cx)
1936 }
1937}
1938
1939#[cfg(feature = "std")]
1940mod error {
1941 use std::error::Error;
1942
1943 use super::Box;
1944
1945 #[cfg(not(no_global_oom_handling))]
1946 impl<'a, E: Error + 'a> From<E> for Box<dyn Error + 'a> {
1947 /// Converts a type of [`Error`] into a box of dyn [`Error`].
1948 ///
1949 /// # Examples
1950 ///
1951 /// ```
1952 /// use std::error::Error;
1953 /// use std::fmt;
1954 /// use std::mem;
1955 ///
1956 /// #[derive(Debug)]
1957 /// struct AnError;
1958 ///
1959 /// impl fmt::Display for AnError {
1960 /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1961 /// write!(f, "An error")
1962 /// }
1963 /// }
1964 ///
1965 /// impl Error for AnError {}
1966 ///
1967 /// let an_error = AnError;
1968 /// assert!(0 == mem::size_of_val(&an_error));
1969 /// let a_boxed_error = Box::<dyn Error>::from(an_error);
1970 /// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))
1971 /// ```
1972 #[inline(always)]
1973 fn from(err: E) -> Box<dyn Error + 'a> {
1974 unsafe { Box::from_raw(Box::leak(Box::new(err))) }
1975 }
1976 }
1977
1978 #[cfg(not(no_global_oom_handling))]
1979 impl<'a, E: Error + Send + Sync + 'a> From<E> for Box<dyn Error + Send + Sync + 'a> {
1980 /// Converts a type of [`Error`] + [`Send`] + [`Sync`] into a box of
1981 /// dyn [`Error`] + [`Send`] + [`Sync`].
1982 ///
1983 /// # Examples
1984 ///
1985 /// ```
1986 /// use std::error::Error;
1987 /// use std::fmt;
1988 /// use std::mem;
1989 ///
1990 /// #[derive(Debug)]
1991 /// struct AnError;
1992 ///
1993 /// impl fmt::Display for AnError {
1994 /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1995 /// write!(f, "An error")
1996 /// }
1997 /// }
1998 ///
1999 /// impl Error for AnError {}
2000 ///
2001 /// unsafe impl Send for AnError {}
2002 ///
2003 /// unsafe impl Sync for AnError {}
2004 ///
2005 /// let an_error = AnError;
2006 /// assert!(0 == mem::size_of_val(&an_error));
2007 /// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(an_error);
2008 /// assert!(
2009 /// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))
2010 /// ```
2011 #[inline(always)]
2012 fn from(err: E) -> Box<dyn Error + Send + Sync + 'a> {
2013 unsafe { Box::from_raw(Box::leak(Box::new(err))) }
2014 }
2015 }
2016
2017 impl<T: Error> Error for Box<T> {
2018 #[inline(always)]
2019 fn source(&self) -> Option<&(dyn Error + 'static)> {
2020 Error::source(&**self)
2021 }
2022 }
2023}
2024
2025#[cfg(feature = "std")]
2026impl<R: std::io::Read + ?Sized, A: Allocator> std::io::Read for Box<R, A> {
2027 #[inline]
2028 fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
2029 (**self).read(buf)
2030 }
2031
2032 #[inline]
2033 fn read_to_end(&mut self, buf: &mut std::vec::Vec<u8>) -> std::io::Result<usize> {
2034 (**self).read_to_end(buf)
2035 }
2036
2037 #[inline]
2038 fn read_to_string(&mut self, buf: &mut String) -> std::io::Result<usize> {
2039 (**self).read_to_string(buf)
2040 }
2041
2042 #[inline]
2043 fn read_exact(&mut self, buf: &mut [u8]) -> std::io::Result<()> {
2044 (**self).read_exact(buf)
2045 }
2046}
2047
2048#[cfg(feature = "std")]
2049impl<W: std::io::Write + ?Sized, A: Allocator> std::io::Write for Box<W, A> {
2050 #[inline]
2051 fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
2052 (**self).write(buf)
2053 }
2054
2055 #[inline]
2056 fn flush(&mut self) -> std::io::Result<()> {
2057 (**self).flush()
2058 }
2059
2060 #[inline]
2061 fn write_all(&mut self, buf: &[u8]) -> std::io::Result<()> {
2062 (**self).write_all(buf)
2063 }
2064
2065 #[inline]
2066 fn write_fmt(&mut self, fmt: fmt::Arguments<'_>) -> std::io::Result<()> {
2067 (**self).write_fmt(fmt)
2068 }
2069}
2070
2071#[cfg(feature = "std")]
2072impl<S: std::io::Seek + ?Sized, A: Allocator> std::io::Seek for Box<S, A> {
2073 #[inline]
2074 fn seek(&mut self, pos: std::io::SeekFrom) -> std::io::Result<u64> {
2075 (**self).seek(pos)
2076 }
2077
2078 #[inline]
2079 fn stream_position(&mut self) -> std::io::Result<u64> {
2080 (**self).stream_position()
2081 }
2082}
2083
2084#[cfg(feature = "std")]
2085impl<B: std::io::BufRead + ?Sized, A: Allocator> std::io::BufRead for Box<B, A> {
2086 #[inline]
2087 fn fill_buf(&mut self) -> std::io::Result<&[u8]> {
2088 (**self).fill_buf()
2089 }
2090
2091 #[inline]
2092 fn consume(&mut self, amt: usize) {
2093 (**self).consume(amt)
2094 }
2095
2096 #[inline]
2097 fn read_until(&mut self, byte: u8, buf: &mut std::vec::Vec<u8>) -> std::io::Result<usize> {
2098 (**self).read_until(byte, buf)
2099 }
2100
2101 #[inline]
2102 fn read_line(&mut self, buf: &mut std::string::String) -> std::io::Result<usize> {
2103 (**self).read_line(buf)
2104 }
2105}
2106
2107#[cfg(feature = "alloc")]
2108impl<A: Allocator> Extend<Box<str, A>> for alloc_crate::string::String {
2109 fn extend<I: IntoIterator<Item = Box<str, A>>>(&mut self, iter: I) {
2110 iter.into_iter().for_each(move |s: Box| self.push_str(&s));
2111 }
2112}
2113
2114#[cfg(not(no_global_oom_handling))]
2115impl Clone for Box<core::ffi::CStr> {
2116 #[inline]
2117 fn clone(&self) -> Self {
2118 (**self).into()
2119 }
2120}
2121
2122#[cfg(not(no_global_oom_handling))]
2123impl From<&core::ffi::CStr> for Box<core::ffi::CStr> {
2124 /// Converts a `&CStr` into a `Box<CStr>`,
2125 /// by copying the contents into a newly allocated [`Box`].
2126 fn from(s: &core::ffi::CStr) -> Box<core::ffi::CStr> {
2127 let boxed: Box<[u8]> = Box::from(s.to_bytes_with_nul());
2128 unsafe { Box::from_raw(Box::into_raw(boxed) as *mut core::ffi::CStr) }
2129 }
2130}
2131
2132#[cfg(feature = "serde")]
2133impl<T, A> serde::Serialize for Box<T, A>
2134where
2135 T: serde::Serialize,
2136 A: Allocator,
2137{
2138 #[inline(always)]
2139 fn serialize<S: serde::ser::Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
2140 (**self).serialize(serializer)
2141 }
2142}
2143
2144#[cfg(feature = "serde")]
2145impl<'de, T, A> serde::Deserialize<'de> for Box<T, A>
2146where
2147 T: serde::Deserialize<'de>,
2148 A: Allocator + Default,
2149{
2150 #[inline(always)]
2151 fn deserialize<D: serde::de::Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
2152 let value = T::deserialize(deserializer)?;
2153 Ok(Box::new_in(value, A::default()))
2154 }
2155}
2156