1 //! Types which pin data to its location in memory
3 //! It is sometimes useful to have objects that are guaranteed to not move,
4 //! in the sense that their placement in memory does not change, and can thus be relied upon.
5 //! A prime example of such a scenario would be building self-referential structs,
6 //! since moving an object with pointers to itself will invalidate them,
7 //! which could cause undefined behavior.
9 //! [`Pin`] ensures that the pointee of any pointer type has a stable location in memory,
10 //! meaning it cannot be moved elsewhere and its memory cannot be deallocated
11 //! until it gets dropped. We say that the pointee is "pinned".
13 //! By default, all types in Rust are movable. Rust allows passing all types by-value,
14 //! and common smart-pointer types such as `Box` and `&mut` allow replacing and
15 //! moving the values they contain: you can move out of a `Box`, or you can use [`mem::swap`].
16 //! [`Pin`] wraps a pointer type, so `Pin<Box<T>>` functions much like a regular `Box<T>`
17 //! (when a `Pin<Box<T>>` gets dropped, so do its contents, and the memory gets deallocated).
18 //! Similarily, `Pin<&mut T>` is a lot like `&mut T`. However, [`Pin`] does not let clients actually
19 //! obtain a `Box<T>` or `&mut T` to pinned data, which implies that you cannot use
20 //! operations such as [`mem::swap`]:
22 //! use std::pin::Pin;
23 //! fn swap_pins<T>(x: Pin<&mut T>, y: Pin<&mut T>) {
24 //! // `mem::swap` needs `&mut T`, but we cannot get it.
25 //! // We are stuck, we cannot swap the contents of these references.
26 //! // We could use `Pin::get_unchecked_mut`, but that is unsafe for a reason:
27 //! // we are not allowed to use it for moving things out of the `Pin`.
31 //! It is worth reiterating that [`Pin`] does *not* change the fact that a Rust compiler
32 //! considers all types movable. [`mem::swap`] remains callable for any `T`. Instead, `Pin`
33 //! prevents certain *values* (pointed to by pointers wrapped in `Pin`) from being
34 //! moved by making it impossible to call methods that require `&mut T` on them
35 //! (like [`mem::swap`]).
37 //! [`Pin`] can be used to wrap any pointer type, and as such it interacts with
38 //! [`Deref`] and [`DerefMut`]. A `Pin<P>` where `P: Deref` should be considered
39 //! as a "`P`-style pointer" to a pinned `P::Target` -- so, a `Pin<Box<T>>` is
40 //! an owned pointer to a pinned `T`, and a `Pin<Rc<T>>` is a reference-counted
41 //! pointer to a pinned `T`.
42 //! For correctness, [`Pin`] relies on the [`Deref`] and [`DerefMut`] implementations
43 //! to not move out of their `self` parameter, and to only ever return a pointer
44 //! to pinned data when they are called on a pinned pointer.
48 //! However, these restrictions are usually not necessary. Many types are always freely
49 //! movable, even when pinned, because they do not rely on having a stable address.
50 //! This includes all the basic types (`bool`, `i32` and friends, references)
51 //! as well as types consisting solely of these types.
52 //! Types that do not care about pinning implement the [`Unpin`] auto-trait, which
53 //! nullifies the effect of [`Pin`]. For `T: Unpin`, `Pin<Box<T>>` and `Box<T>` function
54 //! identically, as do `Pin<&mut T>` and `&mut T`.
56 //! Note that pinning and `Unpin` only affect the pointed-to type, not the pointer
57 //! type itself that got wrapped in `Pin`. For example, whether or not `Box<T>` is
58 //! `Unpin` has no effect on the behavior of `Pin<Box<T>>` (here, `T` is the
61 //! # Example: self-referential struct
64 //! use std::pin::Pin;
65 //! use std::marker::PhantomPinned;
66 //! use std::ptr::NonNull;
68 //! // This is a self-referential struct since the slice field points to the data field.
69 //! // We cannot inform the compiler about that with a normal reference,
70 //! // since this pattern cannot be described with the usual borrowing rules.
71 //! // Instead we use a raw pointer, though one which is known to not be null,
72 //! // since we know it's pointing at the string.
73 //! struct Unmovable {
75 //! slice: NonNull<String>,
76 //! _pin: PhantomPinned,
80 //! // To ensure the data doesn't move when the function returns,
81 //! // we place it in the heap where it will stay for the lifetime of the object,
82 //! // and the only way to access it would be through a pointer to it.
83 //! fn new(data: String) -> Pin<Box<Self>> {
84 //! let res = Unmovable {
86 //! // we only create the pointer once the data is in place
87 //! // otherwise it will have already moved before we even started
88 //! slice: NonNull::dangling(),
89 //! _pin: PhantomPinned,
91 //! let mut boxed = Box::pin(res);
93 //! let slice = NonNull::from(&boxed.data);
94 //! // we know this is safe because modifying a field doesn't move the whole struct
96 //! let mut_ref: Pin<&mut Self> = Pin::as_mut(&mut boxed);
97 //! Pin::get_unchecked_mut(mut_ref).slice = slice;
103 //! let unmoved = Unmovable::new("hello".to_string());
104 //! // The pointer should point to the correct location,
105 //! // so long as the struct hasn't moved.
106 //! // Meanwhile, we are free to move the pointer around.
107 //! # #[allow(unused_mut)]
108 //! let mut still_unmoved = unmoved;
109 //! assert_eq!(still_unmoved.slice, NonNull::from(&still_unmoved.data));
111 //! // Since our type doesn't implement Unpin, this will fail to compile:
112 //! // let new_unmoved = Unmovable::new("world".to_string());
113 //! // std::mem::swap(&mut *still_unmoved, &mut *new_unmoved);
116 //! # Example: intrusive doubly-linked list
118 //! In an intrusive doubly-linked list, the collection does not actually allocate
119 //! the memory for the elements itself. Allocation is controlled by the clients,
120 //! and elements can live on a stack frame that lives shorter than the collection does.
122 //! To make this work, every element has pointers to its predecessor and successor in
123 //! the list. Element can only be added when they are pinned, because moving the elements
124 //! around would invalidate the pointers. Moreover, the `Drop` implementation of a linked
125 //! list element will patch the pointers of its predecessor and successor to remove itself
128 //! Crucially, we have to be able to rely on `drop` being called. If an element
129 //! could be deallocated or otherwise invalidated without calling `drop`, the pointers into it
130 //! from its neighbouring elements would become invalid, which would break the data structure.
132 //! This is why pinning also comes with a `drop`-related guarantee.
134 //! # `Drop` guarantee
136 //! The purpose of pinning is to be able to rely on the placement of some data in memory.
137 //! To make this work, not just moving the data is restricted; deallocating, repurposing or
138 //! otherwise invalidating the memory used to store the data is restricted, too.
139 //! Concretely, for pinned data you have to maintain the invariant
140 //! that *its memory will not get invalidated from the moment it gets pinned until
141 //! when `drop` is called*. Memory can be invalidated by deallocation, but also by
142 //! replacing a `Some(v)` by `None`, or calling `Vec::set_len` to "kill" some elements
145 //! This is exactly the kind of guarantee that the intrusive linked list from the previous
146 //! section needs to function correctly.
148 //! Notice that this guarantee does *not* mean that memory does not leak! It is still
149 //! completely okay not to ever call `drop` on a pinned element (e.g., you can still
150 //! call [`mem::forget`] on a `Pin<Box<T>>`). In the example of the doubly-linked
151 //! list, that element would just stay in the list. However you may not free or reuse the storage
152 //! *without calling `drop`*.
154 //! # `Drop` implementation
156 //! If your type uses pinning (such as the two examples above), you have to be careful
157 //! when implementing `Drop`. The `drop` function takes `&mut self`, but this
158 //! is called *even if your type was previously pinned*! It is as if the
159 //! compiler automatically called `get_unchecked_mut`.
161 //! This can never cause a problem in safe code because implementing a type that relies on pinning
162 //! requires unsafe code, but be aware that deciding to make use of pinning
163 //! in your type (for example by implementing some operation on `Pin<&[mut] Self>`)
164 //! has consequences for your `Drop` implementation as well: if an element
165 //! of your type could have been pinned, you must treat Drop as implicitly taking
166 //! `Pin<&mut Self>`.
168 //! In particular, if your type is `#[repr(packed)]`, the compiler will automatically
169 //! move fields around to be able to drop them. As a consequence, you cannot use
170 //! pinning with a `#[repr(packed)]` type.
172 //! # Projections and Structural Pinning
174 //! One interesting question arises when considering the interaction of pinning and
175 //! the fields of a struct. When can a struct have a "pinning projection", i.e.,
176 //! an operation with type `fn(Pin<&[mut] Struct>) -> Pin<&[mut] Field>`?
177 //! In a similar vein, when can a container type (such as `Vec`, `Box`, or `RefCell`)
178 //! have an operation with type `fn(Pin<&[mut] Container<T>>) -> Pin<&[mut] T>`?
180 //! This question is closely related to the question of whether pinning is "structural":
181 //! when you have pinned a wrapper type, have you pinned its contents? Deciding this
182 //! is entirely up to the author of any given type. However, adding a
183 //! projection to the API answers that question with a "yes" by offering pinned access
184 //! to the contents. In that case, there are a couple requirements to be upheld:
186 //! 1. The wrapper must only be [`Unpin`] if all the fields one can project to are
187 //! `Unpin`. This is the default, but `Unpin` is a safe trait, so as the author of
188 //! the wrapper it is your responsibility *not* to add something like
189 //! `impl<T> Unpin for Container<T>`. (Notice that adding a projection operation
190 //! requires unsafe code, so the fact that `Unpin` is a safe trait does not break
191 //! the principle that you only have to worry about any of this if you use `unsafe`.)
192 //! 2. The destructor of the wrapper must not move out of its argument. This is the exact
193 //! point that was raised in the [previous section][drop-impl]: `drop` takes `&mut self`,
194 //! but the wrapper (and hence its fields) might have been pinned before.
195 //! You have to guarantee that you do not move a field inside your `Drop` implementation.
196 //! 3. Your wrapper type must *not* be `#[repr(packed)]`. Packed structs have their fields
197 //! moved around when they are dropped to properly align them, which is in conflict with
198 //! claiming that the fields are pinned when your struct is.
199 //! 4. You must make sure that you uphold the [`Drop` guarantee][drop-guarantee]:
200 //! once your wrapper is pinned, the memory that contains the
201 //! content is not overwritten or deallocated without calling the content's destructors.
202 //! This can be tricky, as witnessed by `VecDeque`: the destructor of `VecDeque` can fail
203 //! to call `drop` on all elements if one of the destructors panics. This violates the
204 //! `Drop` guarantee, because it can lead to elements being deallocated without
205 //! their destructor being called. (`VecDeque` has no pinning projections, so this
206 //! does not cause unsoundness.)
207 //! 5. You must not offer any other operations that could lead to data being moved out of
208 //! the fields when your type is pinned. This is usually not a concern, but can become
209 //! tricky when interior mutability is involved. For example, imagine if `RefCell`
210 //! had a method `fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut T>`.
211 //! Then we could do the following:
213 //! fn exploit_ref_cell<T>(rc: Pin<&mut RefCell<T>) {
214 //! { let p = rc.as_mut().get_pin_mut(); } // here we get pinned access to the `T`
215 //! let rc_shr: &RefCell<T> = rc.into_ref().get_ref();
216 //! let b = rc_shr.borrow_mut();
217 //! let content = &mut *b; // and here we have `&mut T` to the same data
220 //! This is catastrophic, it means we can first pin the content of the `RefCell`
221 //! (using `RefCell::get_pin_mut`) and then move that content using the mutable
222 //! reference we got later.
224 //! On the other hand, if you decide *not* to offer any pinning projections, you
225 //! are free to `impl<T> Unpin for Container<T>`. In the standard library,
226 //! this is done for all pointer types: `Box<T>: Unpin` holds for all `T`.
227 //! It makes sense to do this for pointer types, because moving the `Box<T>`
228 //! does not actually move the `T`: the `Box<T>` can be freely movable even if the `T`
229 //! is not. In fact, even `Pin<Box<T>>` and `Pin<&mut T>` are always `Unpin` themselves,
230 //! for the same reason.
232 //! [`Pin`]: struct.Pin.html
233 //! [`Unpin`]: ../../std/marker/trait.Unpin.html
234 //! [`Deref`]: ../../std/ops/trait.Deref.html
235 //! [`DerefMut`]: ../../std/ops/trait.DerefMut.html
236 //! [`mem::swap`]: ../../std/mem/fn.swap.html
237 //! [`mem::forget`]: ../../std/mem/fn.forget.html
238 //! [`Box`]: ../../std/boxed/struct.Box.html
239 //! [drop-impl]: #drop-implementation
240 //! [drop-guarantee]: #drop-guarantee
242 #![stable(feature = "pin", since = "1.33.0")]
245 use marker::{Sized, Unpin};
246 use cmp::{self, PartialEq, PartialOrd};
247 use ops::{Deref, DerefMut, Receiver, CoerceUnsized, DispatchFromDyn};
249 /// A pinned pointer.
251 /// This is a wrapper around a kind of pointer which makes that pointer "pin" its
252 /// value in place, preventing the value referenced by that pointer from being moved
253 /// unless it implements [`Unpin`].
255 /// See the [`pin` module] documentation for further explanation on pinning.
257 /// [`Unpin`]: ../../std/marker/trait.Unpin.html
258 /// [`pin` module]: ../../std/pin/index.html
260 // Note: the derives below, and the explicit `PartialEq` and `PartialOrd`
261 // implementations, are allowed because they all only use `&P`, so they cannot move
262 // the value behind `pointer`.
263 #[stable(feature = "pin", since = "1.33.0")]
264 #[cfg_attr(not(stage0), lang = "pin")]
267 #[derive(Copy, Clone, Hash, Eq, Ord)]
272 #[stable(feature = "pin_partialeq_partialord_impl_applicability", since = "1.34.0")]
273 impl<P, Q> PartialEq<Pin<Q>> for Pin<P>
277 fn eq(&self, other: &Pin<Q>) -> bool {
278 self.pointer == other.pointer
281 fn ne(&self, other: &Pin<Q>) -> bool {
282 self.pointer != other.pointer
286 #[stable(feature = "pin_partialeq_partialord_impl_applicability", since = "1.34.0")]
287 impl<P, Q> PartialOrd<Pin<Q>> for Pin<P>
291 fn partial_cmp(&self, other: &Pin<Q>) -> Option<cmp::Ordering> {
292 self.pointer.partial_cmp(&other.pointer)
295 fn lt(&self, other: &Pin<Q>) -> bool {
296 self.pointer < other.pointer
299 fn le(&self, other: &Pin<Q>) -> bool {
300 self.pointer <= other.pointer
303 fn gt(&self, other: &Pin<Q>) -> bool {
304 self.pointer > other.pointer
307 fn ge(&self, other: &Pin<Q>) -> bool {
308 self.pointer >= other.pointer
312 impl<P: Deref> Pin<P>
316 /// Construct a new `Pin` around a pointer to some data of a type that
317 /// implements [`Unpin`].
319 /// Unlike `Pin::new_unchecked`, this method is safe because the pointer
320 /// `P` dereferences to an [`Unpin`] type, which nullifies the pinning guarantees.
322 /// [`Unpin`]: ../../std/marker/trait.Unpin.html
323 #[stable(feature = "pin", since = "1.33.0")]
325 pub fn new(pointer: P) -> Pin<P> {
326 // Safety: the value pointed to is `Unpin`, and so has no requirements
328 unsafe { Pin::new_unchecked(pointer) }
332 impl<P: Deref> Pin<P> {
333 /// Construct a new `Pin` around a reference to some data of a type that
334 /// may or may not implement `Unpin`.
336 /// If `pointer` dereferences to an `Unpin` type, `Pin::new` should be used
341 /// This constructor is unsafe because we cannot guarantee that the data
342 /// pointed to by `pointer` is pinned, meaning that the data will not be moved or
343 /// its storage invalidated until it gets dropped. If the constructed `Pin<P>` does
344 /// not guarantee that the data `P` points to is pinned, constructing a
345 /// `Pin<P>` is unsafe.
347 /// By using this method, you are making a promise about the `P::Deref` and
348 /// `P::DerefMut` implementations, if they exist. Most importantly, they
349 /// must not move out of their `self` arguments: `Pin::as_mut` and `Pin::as_ref`
350 /// will call `DerefMut::deref_mut` and `Deref::deref` *on the pinned pointer*
351 /// and expect these methods to uphold the pinning invariants.
352 /// Moreover, by calling this method you promise that the reference `P`
353 /// dereferences to will not be moved out of again; in particular, it
354 /// must not be possible to obtain a `&mut P::Target` and then
355 /// move out of that reference (using, for example [`mem::swap`]).
357 /// For example, calling `Pin::new_unchecked` on an `&'a mut T` is unsafe because
358 /// while you are able to pin it for the given lifetime `'a`, you have no control
359 /// over whether it is kept pinned once `'a` ends:
362 /// use std::pin::Pin;
364 /// fn move_pinned_ref<T>(mut a: T, mut b: T) {
365 /// unsafe { let p = Pin::new_unchecked(&mut a); } // should mean `a` can never move again
366 /// mem::swap(&mut a, &mut b);
367 /// // the address of `a` changed to `b`'s stack slot, so `a` got moved even
368 /// // though we have previously pinned it!
371 /// A value, once pinned, must remain pinned forever (unless its type implements `Unpin`).
373 /// Similarily, calling `Pin::new_unchecked` on a `Rc<T>` is unsafe because there could be
374 /// aliases to the same data that are not subject to the pinning restrictions:
377 /// use std::pin::Pin;
379 /// fn move_pinned_rc<T>(mut x: Rc<T>) {
380 /// let pinned = unsafe { Pin::new_unchecked(x.clone()) };
381 /// { let p: Pin<&T> = pinned.as_ref(); } // should mean the pointee can never move again
383 /// let content = Rc::get_mut(&mut x).unwrap();
384 /// // Now, if `x` was the only reference, we have a mutable reference to
385 /// // data that we pinned above, which we could use to move it as we have
386 /// // seen in the previous example.
390 /// [`mem::swap`]: ../../std/mem/fn.swap.html
391 #[stable(feature = "pin", since = "1.33.0")]
393 pub unsafe fn new_unchecked(pointer: P) -> Pin<P> {
397 /// Gets a pinned shared reference from this pinned pointer.
399 /// This is a generic method to go from `&Pin<Pointer<T>>` to `Pin<&T>`.
400 /// It is safe because, as part of the contract of `Pin::new_unchecked`,
401 /// the pointee cannot move after `Pin<Pointer<T>>` got created.
402 /// "Malicious" implementations of `Pointer::Deref` are likewise
403 /// ruled out by the contract of `Pin::new_unchecked`.
404 #[stable(feature = "pin", since = "1.33.0")]
406 pub fn as_ref(self: &Pin<P>) -> Pin<&P::Target> {
407 unsafe { Pin::new_unchecked(&*self.pointer) }
411 impl<P: DerefMut> Pin<P> {
412 /// Gets a pinned mutable reference from this pinned pointer.
414 /// This is a generic method to go from `&mut Pin<Pointer<T>>` to `Pin<&mut T>`.
415 /// It is safe because, as part of the contract of `Pin::new_unchecked`,
416 /// the pointee cannot move after `Pin<Pointer<T>>` got created.
417 /// "Malicious" implementations of `Pointer::DerefMut` are likewise
418 /// ruled out by the contract of `Pin::new_unchecked`.
419 #[stable(feature = "pin", since = "1.33.0")]
421 pub fn as_mut(self: &mut Pin<P>) -> Pin<&mut P::Target> {
422 unsafe { Pin::new_unchecked(&mut *self.pointer) }
425 /// Assigns a new value to the memory behind the pinned reference.
427 /// This overwrites pinned data, but that is okay: its destructor gets
428 /// run before being overwritten, so no pinning guarantee is violated.
429 #[stable(feature = "pin", since = "1.33.0")]
431 pub fn set(self: &mut Pin<P>, value: P::Target)
435 *(self.pointer) = value;
439 impl<'a, T: ?Sized> Pin<&'a T> {
440 /// Constructs a new pin by mapping the interior value.
442 /// For example, if you wanted to get a `Pin` of a field of something,
443 /// you could use this to get access to that field in one line of code.
444 /// However, there are several gotchas with these "pinning projections";
445 /// see the [`pin` module] documentation for further details on that topic.
449 /// This function is unsafe. You must guarantee that the data you return
450 /// will not move so long as the argument value does not move (for example,
451 /// because it is one of the fields of that value), and also that you do
452 /// not move out of the argument you receive to the interior function.
454 /// [`pin` module]: ../../std/pin/index.html#projections-and-structural-pinning
455 #[stable(feature = "pin", since = "1.33.0")]
456 pub unsafe fn map_unchecked<U, F>(self: Pin<&'a T>, func: F) -> Pin<&'a U> where
459 let pointer = &*self.pointer;
460 let new_pointer = func(pointer);
461 Pin::new_unchecked(new_pointer)
464 /// Gets a shared reference out of a pin.
466 /// This is safe because it is not possible to move out of a shared reference.
467 /// It may seem like there is an issue here with interior mutability: in fact,
468 /// it *is* possible to move a `T` out of a `&RefCell<T>`. However, this is
469 /// not a problem as long as there does not also exist a `Pin<&T>` pointing
470 /// to the same data, and `RefCell` does not let you create a pinned reference
471 /// to its contents. See the discussion on ["pinning projections"] for further
474 /// Note: `Pin` also implements `Deref` to the target, which can be used
475 /// to access the inner value. However, `Deref` only provides a reference
476 /// that lives for as long as the borrow of the `Pin`, not the lifetime of
477 /// the `Pin` itself. This method allows turning the `Pin` into a reference
478 /// with the same lifetime as the original `Pin`.
480 /// ["pinning projections"]: ../../std/pin/index.html#projections-and-structural-pinning
481 #[stable(feature = "pin", since = "1.33.0")]
483 pub fn get_ref(self: Pin<&'a T>) -> &'a T {
488 impl<'a, T: ?Sized> Pin<&'a mut T> {
489 /// Converts this `Pin<&mut T>` into a `Pin<&T>` with the same lifetime.
490 #[stable(feature = "pin", since = "1.33.0")]
492 pub fn into_ref(self: Pin<&'a mut T>) -> Pin<&'a T> {
493 Pin { pointer: self.pointer }
496 /// Gets a mutable reference to the data inside of this `Pin`.
498 /// This requires that the data inside this `Pin` is `Unpin`.
500 /// Note: `Pin` also implements `DerefMut` to the data, which can be used
501 /// to access the inner value. However, `DerefMut` only provides a reference
502 /// that lives for as long as the borrow of the `Pin`, not the lifetime of
503 /// the `Pin` itself. This method allows turning the `Pin` into a reference
504 /// with the same lifetime as the original `Pin`.
505 #[stable(feature = "pin", since = "1.33.0")]
507 pub fn get_mut(self: Pin<&'a mut T>) -> &'a mut T
513 /// Gets a mutable reference to the data inside of this `Pin`.
517 /// This function is unsafe. You must guarantee that you will never move
518 /// the data out of the mutable reference you receive when you call this
519 /// function, so that the invariants on the `Pin` type can be upheld.
521 /// If the underlying data is `Unpin`, `Pin::get_mut` should be used
523 #[stable(feature = "pin", since = "1.33.0")]
525 pub unsafe fn get_unchecked_mut(self: Pin<&'a mut T>) -> &'a mut T {
529 /// Construct a new pin by mapping the interior value.
531 /// For example, if you wanted to get a `Pin` of a field of something,
532 /// you could use this to get access to that field in one line of code.
533 /// However, there are several gotchas with these "pinning projections";
534 /// see the [`pin` module] documentation for further details on that topic.
538 /// This function is unsafe. You must guarantee that the data you return
539 /// will not move so long as the argument value does not move (for example,
540 /// because it is one of the fields of that value), and also that you do
541 /// not move out of the argument you receive to the interior function.
543 /// [`pin` module]: ../../std/pin/index.html#projections-and-structural-pinning
544 #[stable(feature = "pin", since = "1.33.0")]
545 pub unsafe fn map_unchecked_mut<U, F>(self: Pin<&'a mut T>, func: F) -> Pin<&'a mut U> where
546 F: FnOnce(&mut T) -> &mut U,
548 let pointer = Pin::get_unchecked_mut(self);
549 let new_pointer = func(pointer);
550 Pin::new_unchecked(new_pointer)
554 #[stable(feature = "pin", since = "1.33.0")]
555 impl<P: Deref> Deref for Pin<P> {
556 type Target = P::Target;
557 fn deref(&self) -> &P::Target {
558 Pin::get_ref(Pin::as_ref(self))
562 #[stable(feature = "pin", since = "1.33.0")]
563 impl<P: DerefMut> DerefMut for Pin<P>
567 fn deref_mut(&mut self) -> &mut P::Target {
568 Pin::get_mut(Pin::as_mut(self))
572 #[unstable(feature = "receiver_trait", issue = "0")]
573 impl<P: Receiver> Receiver for Pin<P> {}
575 #[stable(feature = "pin", since = "1.33.0")]
576 impl<P: fmt::Debug> fmt::Debug for Pin<P> {
577 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
578 fmt::Debug::fmt(&self.pointer, f)
582 #[stable(feature = "pin", since = "1.33.0")]
583 impl<P: fmt::Display> fmt::Display for Pin<P> {
584 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
585 fmt::Display::fmt(&self.pointer, f)
589 #[stable(feature = "pin", since = "1.33.0")]
590 impl<P: fmt::Pointer> fmt::Pointer for Pin<P> {
591 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
592 fmt::Pointer::fmt(&self.pointer, f)
596 // Note: this means that any impl of `CoerceUnsized` that allows coercing from
597 // a type that impls `Deref<Target=impl !Unpin>` to a type that impls
598 // `Deref<Target=Unpin>` is unsound. Any such impl would probably be unsound
599 // for other reasons, though, so we just need to take care not to allow such
600 // impls to land in std.
601 #[stable(feature = "pin", since = "1.33.0")]
602 impl<P, U> CoerceUnsized<Pin<U>> for Pin<P>
607 #[stable(feature = "pin", since = "1.33.0")]
608 impl<'a, P, U> DispatchFromDyn<Pin<U>> for Pin<P>
610 P: DispatchFromDyn<U>,