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` or reference 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 like [`mem::swap`] on them.
36 //! [`Pin`] can be used to wrap any pointer type, and as such it interacts with
37 //! [`Deref`] and [`DerefMut`]. A `Pin<P>` where `P: Deref` should be considered
38 //! as a "`P`-style pointer" to a pinned `P::Target` -- so, a `Pin<Box<T>>` is
39 //! an owned pointer to a pinned `T`, and a `Pin<Rc<T>>` is a reference-counted
40 //! pointer to a pinned `T`.
41 //! For correctness, [`Pin`] relies on the [`Deref`] and [`DerefMut`] implementations
42 //! to not move out of their `self` parameter, and to only ever return a pointer
43 //! to pinned data when they are called on a pinned pointer.
47 //! However, these restrictions are usually not necessary. Many types are always freely
48 //! movable, even when pinned, because they do not rely on having a stable address.
49 //! This includes all the basic types (`bool`, `i32` and friends, references)
50 //! as well as types consisting solely of these types.
51 //! Types that do not care about pinning implement the [`Unpin`] auto-trait, which
52 //! nullifies the effect of [`Pin`]. For `T: Unpin`, `Pin<Box<T>>` and `Box<T>` function
53 //! identically, as do `Pin<&mut T>` and `&mut T`.
55 //! Note that pinning and `Unpin` only affect the pointed-to type, not the pointer
56 //! type itself that got wrapped in `Pin`. For example, whether or not `Box<T>` is
57 //! `Unpin` has no effect on the behavior of `Pin<Box<T>>` (here, `T` is the
60 //! # Example: self-referential struct
63 //! use std::pin::Pin;
64 //! use std::marker::PhantomPinned;
65 //! use std::ptr::NonNull;
67 //! // This is a self-referential struct since the slice field points to the data field.
68 //! // We cannot inform the compiler about that with a normal reference,
69 //! // since this pattern cannot be described with the usual borrowing rules.
70 //! // Instead we use a raw pointer, though one which is known to not be null,
71 //! // since we know it's pointing at the string.
72 //! struct Unmovable {
74 //! slice: NonNull<String>,
75 //! _pin: PhantomPinned,
79 //! // To ensure the data doesn't move when the function returns,
80 //! // we place it in the heap where it will stay for the lifetime of the object,
81 //! // and the only way to access it would be through a pointer to it.
82 //! fn new(data: String) -> Pin<Box<Self>> {
83 //! let res = Unmovable {
85 //! // we only create the pointer once the data is in place
86 //! // otherwise it will have already moved before we even started
87 //! slice: NonNull::dangling(),
88 //! _pin: PhantomPinned,
90 //! let mut boxed = Box::pin(res);
92 //! let slice = NonNull::from(&boxed.data);
93 //! // we know this is safe because modifying a field doesn't move the whole struct
95 //! let mut_ref: Pin<&mut Self> = Pin::as_mut(&mut boxed);
96 //! Pin::get_unchecked_mut(mut_ref).slice = slice;
102 //! let unmoved = Unmovable::new("hello".to_string());
103 //! // The pointer should point to the correct location,
104 //! // so long as the struct hasn't moved.
105 //! // Meanwhile, we are free to move the pointer around.
106 //! # #[allow(unused_mut)]
107 //! let mut still_unmoved = unmoved;
108 //! assert_eq!(still_unmoved.slice, NonNull::from(&still_unmoved.data));
110 //! // Since our type doesn't implement Unpin, this will fail to compile:
111 //! // let new_unmoved = Unmovable::new("world".to_string());
112 //! // std::mem::swap(&mut *still_unmoved, &mut *new_unmoved);
115 //! # Example: intrusive doubly-linked list
117 //! In an intrusive doubly-linked list, the collection does not actually allocate
118 //! the memory for the elements itself. Allocation is controlled by the clients,
119 //! and elements can live on a stack frame that lives shorter than the collection does.
121 //! To make this work, every element has pointers to its predecessor and successor in
122 //! the list. Element can only be added when they are pinned, because moving the elements
123 //! around would invalidate the pointers. Moreover, the `Drop` implementation of a linked
124 //! list element will patch the pointers of its predecessor and successor to remove itself
127 //! To make this work, it is crucial that we can actually rely on `drop` being called.
128 //! And, in fact, this is a guarantee that `Pin` provides.
130 //! # `Drop` guarantee
132 //! The purpose of pinning is to be able to rely on the placement of some data in memory.
133 //! To make this work, not just moving the data is restricted; deallocating, repurposing or
134 //! otherwise invalidating the memory used to store the data is restricted, too.
135 //! Concretely, for pinned data you have to maintain the invariant
136 //! that *its memory will not get invalidated from the moment it gets pinned until
137 //! when `drop` is called*. Memory can be invalidated by deallocation, but also by
138 //! replacing a `Some(v)` by `None`, or calling `Vec::set_len` to "kill" some elements
141 //! This is exactly the kind of guarantee that the intrusive linked list from the previous
142 //! section needs to function correctly. Clearly, if an element
143 //! could be deallocated or otherwise invalidated without calling `drop`, the pointers into it
144 //! from its neighbouring elements would become invalid, which would break the data structure.
146 //! Notice that this guarantee does *not* mean that memory does not leak! It is still
147 //! completely okay not to ever call `drop` on a pinned element (e.g., you can still
148 //! call [`mem::forget`] on a `Pin<Box<T>>`). In the example of the doubly-linked
149 //! list, that element would just stay in the list. However you may not free or reuse the storage
150 //! *without calling `drop`*.
152 //! # `Drop` implementation
154 //! If your type uses pinning (such as the two examples above), you have to be careful
155 //! when implementing `Drop`. The `drop` function takes `&mut self`, but this
156 //! is called *even if your type was previously pinned*! It is as if the
157 //! compiler automatically called `get_unchecked_mut`.
159 //! This can never cause a problem in safe code because implementing a type that relies on pinning
160 //! requires unsafe code, but be aware that deciding to make use of pinning
161 //! in your type (for example by implementing some operation on `Pin<&[mut] Self>`)
162 //! has consequences for your `Drop` implementation as well: if an element
163 //! of your type could have been pinned, you must treat Drop as implicitly taking
164 //! `Pin<&mut Self>`.
166 //! In particular, if your type is `#[repr(packed)]`, the compiler will automatically
167 //! move fields around to be able to drop them. As a consequence, you cannot use
168 //! pinning with a `#[repr(packed)]` type.
170 //! # Projections and Structural Pinning
172 //! One interesting question arises when considering the interaction of pinning and
173 //! the fields of a struct. When can a struct have a "pinning projection", i.e.,
174 //! an operation with type `fn(Pin<&[mut] Struct>) -> Pin<&[mut] Field>`?
175 //! In a similar vein, when can a container type (such as `Vec`, `Box`, or `RefCell`)
176 //! have an operation with type `fn(Pin<&[mut] Container<T>>) -> Pin<&[mut] T>`?
178 //! This question is closely related to the question of whether pinning is "structural":
179 //! when you have pinned a wrapper type, have you pinned its contents? Deciding this
180 //! is entirely up to the author of any given type. However, adding a
181 //! projection to the API answers that question with a "yes" by offering pinned access
182 //! to the contents. In that case, there are a couple requirements to be upheld:
184 //! 1. The wrapper must only be [`Unpin`] if all the fields one can project to are
185 //! `Unpin`. This is the default, but `Unpin` is a safe trait, so as the author of
186 //! the wrapper it is your responsibility *not* to add something like
187 //! `impl<T> Unpin for Container<T>`. (Notice that adding a projection operation
188 //! requires unsafe code, so the fact that `Unpin` is a safe trait does not break
189 //! the principle that you only have to worry about any of this if you use `unsafe`.)
190 //! 2. The destructor of the wrapper must not move out of its argument. This is the exact
191 //! point that was raised in the [previous section][drop-impl]: `drop` takes `&mut self`,
192 //! but the wrapper (and hence its fields) might have been pinned before.
193 //! You have to guarantee that you do not move a field inside your `Drop` implementation.
194 //! 3. Your wrapper type must *not* be `#[repr(packed)]`. Packed structs have their fields
195 //! moved around when they are dropped to properly align them, which is in conflict with
196 //! claiming that the fields are pinned when your struct is.
197 //! 4. You must make sure that you uphold the [`Drop` guarantee][drop-guarantee]:
198 //! once your wrapper is pinned, the memory that contains the
199 //! content is not overwritten or deallocated without calling the content's destructors.
200 //! This can be tricky, as witnessed by `VecDeque`: the destructor of `VecDeque` can fail
201 //! to call `drop` on all elements if one of the destructors panics. This violates the
202 //! `Drop` guarantee, because it can lead to elements being deallocated without
203 //! their destructor being called. (`VecDeque` has no pinning projections, so this
204 //! does not cause unsoundness.)
205 //! 5. You must not offer any other operations that could lead to data being moved out of
206 //! the fields when your type is pinned. This is usually not a concern, but can become
207 //! tricky when interior mutability is involved. For example, imagine `RefCell`
208 //! would have a method `fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut T>`.
209 //! Then we could do the following:
211 //! fn exploit_ref_cell<T>(rc: Pin<&mut RefCell<T>) {
212 //! { let p = rc.as_mut().get_pin_mut(); } // here we get pinned access to the `T`
213 //! let rc_shr: &RefCell<T> = rc.into_ref().get_ref();
214 //! let b = rc_shr.borrow_mut();
215 //! let content = &mut *b; // and here we have `&mut T` to the same data
218 //! This is catastrophic, it means we can first pin the content of the `RefCell`
219 //! (using `RefCell::get_pin_mut`) and then move that content using the mutable
220 //! reference we got later.
222 //! On the other hand, if you decide *not* to offer any pinning projections, you
223 //! are free to `impl<T> Unpin for Container<T>`. In the standard library,
224 //! this is done for all pointer types: `Box<T>: Unpin` holds for all `T`.
225 //! It makes sense to do this for pointer types, because moving the `Box<T>`
226 //! does not actually move the `T`: the `Box<T>` can be freely movable even if the `T`
227 //! is not. In fact, even `Pin<Box<T>>` and `Pin<&mut T>` are always `Unpin` themselves,
228 //! for the same reason.
230 //! [`Pin`]: struct.Pin.html
231 //! [`Unpin`]: ../../std/marker/trait.Unpin.html
232 //! [`Deref`]: ../../std/ops/trait.Deref.html
233 //! [`DerefMut`]: ../../std/ops/trait.DerefMut.html
234 //! [`mem::swap`]: ../../std/mem/fn.swap.html
235 //! [`mem::forget`]: ../../std/mem/fn.forget.html
236 //! [`Box`]: ../../std/boxed/struct.Box.html
237 //! [drop-impl]: #drop-implementation
238 //! [drop-guarantee]: #drop-guarantee
240 #![stable(feature = "pin", since = "1.33.0")]
243 use marker::{Sized, Unpin};
244 use cmp::{self, PartialEq, PartialOrd};
245 use ops::{Deref, DerefMut, Receiver, CoerceUnsized, DispatchFromDyn};
247 /// A pinned pointer.
249 /// This is a wrapper around a kind of pointer which makes that pointer "pin" its
250 /// value in place, preventing the value referenced by that pointer from being moved
251 /// unless it implements [`Unpin`].
253 /// See the [`pin` module] documentation for further explanation on pinning.
255 /// [`Unpin`]: ../../std/marker/trait.Unpin.html
256 /// [`pin` module]: ../../std/pin/index.html
258 // Note: the derives below, and the explicit `PartialEq` and `PartialOrd`
259 // implementations, are allowed because they all only use `&P`, so they cannot move
260 // the value behind `pointer`.
261 #[stable(feature = "pin", since = "1.33.0")]
262 #[cfg_attr(not(stage0), lang = "pin")]
265 #[derive(Copy, Clone, Hash, Eq, Ord)]
270 #[stable(feature = "pin_partialeq_partialord_impl_applicability", since = "1.34.0")]
271 impl<P, Q> PartialEq<Pin<Q>> for Pin<P>
275 fn eq(&self, other: &Pin<Q>) -> bool {
276 self.pointer == other.pointer
279 fn ne(&self, other: &Pin<Q>) -> bool {
280 self.pointer != other.pointer
284 #[stable(feature = "pin_partialeq_partialord_impl_applicability", since = "1.34.0")]
285 impl<P, Q> PartialOrd<Pin<Q>> for Pin<P>
289 fn partial_cmp(&self, other: &Pin<Q>) -> Option<cmp::Ordering> {
290 self.pointer.partial_cmp(&other.pointer)
293 fn lt(&self, other: &Pin<Q>) -> bool {
294 self.pointer < other.pointer
297 fn le(&self, other: &Pin<Q>) -> bool {
298 self.pointer <= other.pointer
301 fn gt(&self, other: &Pin<Q>) -> bool {
302 self.pointer > other.pointer
305 fn ge(&self, other: &Pin<Q>) -> bool {
306 self.pointer >= other.pointer
310 impl<P: Deref> Pin<P>
314 /// Construct a new `Pin` around a pointer to some data of a type that
315 /// implements [`Unpin`].
317 /// Unlike `Pin::new_unchecked`, this method is safe because the pointer
318 /// `P` dereferences to an [`Unpin`] type, which nullifies the pinning guarantees.
320 /// [`Unpin`]: ../../std/marker/trait.Unpin.html
321 #[stable(feature = "pin", since = "1.33.0")]
323 pub fn new(pointer: P) -> Pin<P> {
324 // Safety: the value pointed to is `Unpin`, and so has no requirements
326 unsafe { Pin::new_unchecked(pointer) }
330 impl<P: Deref> Pin<P> {
331 /// Construct a new `Pin` around a reference to some data of a type that
332 /// may or may not implement `Unpin`.
334 /// If `pointer` dereferences to an `Unpin` type, `Pin::new` should be used
339 /// This constructor is unsafe because we cannot guarantee that the data
340 /// pointed to by `pointer` is pinned, meaning that the data will not be moved or
341 /// its storage invalidated until it gets dropped. If the constructed `Pin<P>` does
342 /// not guarantee that the data `P` points to is pinned, constructing a
343 /// `Pin<P>` is unsafe. In particular,
345 /// By using this method, you are making a promise about the `P::Deref` and
346 /// `P::DerefMut` implementations, if they exist. Most importantly, they
347 /// must not move out of their `self` arguments: `Pin::as_mut` and `Pin::as_ref`
348 /// will call `DerefMut::deref_mut` and `Deref::deref` *on the pinned pointer*
349 /// and expect these methods to uphold the pinning invariants.
350 /// Moreover, by calling this method you promise that the reference `P`
351 /// dereferences to will not be moved out of again; in particular, it
352 /// must not be possible to obtain a `&mut P::Target` and then
353 /// move out of that reference (using, for example [`mem::swap`]).
355 /// For example, calling `Pin::new_unchecked`
356 /// on an `&'a mut T` is unsafe because while you are able to pin it for the given
357 /// lifetime `'a`, you have no control over whether it is kept pinned once `'a` ends:
360 /// use std::pin::Pin;
362 /// fn move_pinned_ref<T>(mut a: T, mut b: T) {
363 /// unsafe { let p = Pin::new_unchecked(&mut a); } // should mean `a` can never move again
364 /// mem::swap(&mut a, &mut b);
365 /// // the address of `a` changed to `b`'s stack slot, so `a` got moved even
366 /// // though we have previously pinned it!
369 /// A value, once pinned, must remain pinned forever (unless its type implements `Unpin`).
371 /// Similarily, calling `Pin::new_unchecked` on a `Rc<T>` is unsafe because there could be
372 /// aliases to the same data that are not subject to the pinning restrictions:
375 /// use std::pin::Pin;
377 /// fn move_pinned_rc<T>(mut x: Rc<T>) {
378 /// let pinned = unsafe { Pin::new_unchecked(x.clone()) };
379 /// { let p: Pin<&T> = pinned.as_ref(); } // should mean the pointee can never move again
381 /// let content = Rc::get_mut(&mut x).unwrap();
382 /// // Now, if `x` was the only reference, we have a mutable reference to
383 /// // data that we pinned above, which we could use to move it as we have
384 /// // seen in the previous example.
388 /// [`mem::swap`]: ../../std/mem/fn.swap.html
389 #[stable(feature = "pin", since = "1.33.0")]
391 pub unsafe fn new_unchecked(pointer: P) -> Pin<P> {
395 /// Gets a pinned shared reference from this pinned pointer.
397 /// This is a generic method to go from `&Pin<SmartPointer<T>>` to `Pin<&T>`.
398 /// It is safe because, as part of the contract of `Pin::new_unchecked`,
399 /// the pointee cannot move after `Pin<SmartPointer<T>>` got created.
400 /// "Malicious" implementations of `SmartPointer::Deref` are likewise
401 /// ruled out by the contract of `Pin::new_unchecked`.
402 #[stable(feature = "pin", since = "1.33.0")]
404 pub fn as_ref(self: &Pin<P>) -> Pin<&P::Target> {
405 unsafe { Pin::new_unchecked(&*self.pointer) }
409 impl<P: DerefMut> Pin<P> {
410 /// Gets a pinned mutable reference from this pinned pointer.
412 /// This is a generic method to go from `&mut Pin<SmartPointer<T>>` to `Pin<&mut T>`.
413 /// It is safe because, as part of the contract of `Pin::new_unchecked`,
414 /// the pointee cannot move after `Pin<SmartPointer<T>>` got created.
415 /// "Malicious" implementations of `SmartPointer::DerefMut` are likewise
416 /// ruled out by the contract of `Pin::new_unchecked`.
417 #[stable(feature = "pin", since = "1.33.0")]
419 pub fn as_mut(self: &mut Pin<P>) -> Pin<&mut P::Target> {
420 unsafe { Pin::new_unchecked(&mut *self.pointer) }
423 /// Assigns a new value to the memory behind the pinned reference.
425 /// This overwrites pinned data, but that is okay: its destructor gets
426 /// run before being overwritten, so no pinning guarantee is violated.
427 #[stable(feature = "pin", since = "1.33.0")]
429 pub fn set(self: &mut Pin<P>, value: P::Target)
433 *(self.pointer) = value;
437 impl<'a, T: ?Sized> Pin<&'a T> {
438 /// Constructs a new pin by mapping the interior value.
440 /// For example, if you wanted to get a `Pin` of a field of something,
441 /// you could use this to get access to that field in one line of code.
442 /// However, there are several gotchas with these "pinning projections";
443 /// see the [`pin` module] documentation for further details on that topic.
447 /// This function is unsafe. You must guarantee that the data you return
448 /// will not move so long as the argument value does not move (for example,
449 /// because it is one of the fields of that value), and also that you do
450 /// not move out of the argument you receive to the interior function.
452 /// [`pin` module]: ../../std/pin/index.html#projections-and-structural-pinning
453 #[stable(feature = "pin", since = "1.33.0")]
454 pub unsafe fn map_unchecked<U, F>(self: Pin<&'a T>, func: F) -> Pin<&'a U> where
457 let pointer = &*self.pointer;
458 let new_pointer = func(pointer);
459 Pin::new_unchecked(new_pointer)
462 /// Gets a shared reference out of a pin.
464 /// This is safe because it is not possible to move out of a shared reference.
465 /// It may seem like there is an issue here with interior mutability: in fact,
466 /// it *is* possible to move a `T` out of a `&RefCell<T>`. However, this is
467 /// not a problem as long as there does not also exist a `Pin<&T>` pointing
468 /// to the same data, and `RefCell` does not let you create a pinned reference
469 /// to its contents. See the discussion on ["pinning projections"] for further
472 /// Note: `Pin` also implements `Deref` to the target, which can be used
473 /// to access the inner value. However, `Deref` only provides a reference
474 /// that lives for as long as the borrow of the `Pin`, not the lifetime of
475 /// the `Pin` itself. This method allows turning the `Pin` into a reference
476 /// with the same lifetime as the original `Pin`.
478 /// ["pinning projections"]: ../../std/pin/index.html#projections-and-structural-pinning
479 #[stable(feature = "pin", since = "1.33.0")]
481 pub fn get_ref(self: Pin<&'a T>) -> &'a T {
486 impl<'a, T: ?Sized> Pin<&'a mut T> {
487 /// Converts this `Pin<&mut T>` into a `Pin<&T>` with the same lifetime.
488 #[stable(feature = "pin", since = "1.33.0")]
490 pub fn into_ref(self: Pin<&'a mut T>) -> Pin<&'a T> {
491 Pin { pointer: self.pointer }
494 /// Gets a mutable reference to the data inside of this `Pin`.
496 /// This requires that the data inside this `Pin` is `Unpin`.
498 /// Note: `Pin` also implements `DerefMut` to the data, which can be used
499 /// to access the inner value. However, `DerefMut` only provides a reference
500 /// that lives for as long as the borrow of the `Pin`, not the lifetime of
501 /// the `Pin` itself. This method allows turning the `Pin` into a reference
502 /// with the same lifetime as the original `Pin`.
503 #[stable(feature = "pin", since = "1.33.0")]
505 pub fn get_mut(self: Pin<&'a mut T>) -> &'a mut T
511 /// Gets a mutable reference to the data inside of this `Pin`.
515 /// This function is unsafe. You must guarantee that you will never move
516 /// the data out of the mutable reference you receive when you call this
517 /// function, so that the invariants on the `Pin` type can be upheld.
519 /// If the underlying data is `Unpin`, `Pin::get_mut` should be used
521 #[stable(feature = "pin", since = "1.33.0")]
523 pub unsafe fn get_unchecked_mut(self: Pin<&'a mut T>) -> &'a mut T {
527 /// Construct a new pin by mapping the interior value.
529 /// For example, if you wanted to get a `Pin` of a field of something,
530 /// you could use this to get access to that field in one line of code.
531 /// However, there are several gotchas with these "pinning projections";
532 /// see the [`pin` module] documentation for further details on that topic.
536 /// This function is unsafe. You must guarantee that the data you return
537 /// will not move so long as the argument value does not move (for example,
538 /// because it is one of the fields of that value), and also that you do
539 /// not move out of the argument you receive to the interior function.
541 /// [`pin` module]: ../../std/pin/index.html#projections-and-structural-pinning
542 #[stable(feature = "pin", since = "1.33.0")]
543 pub unsafe fn map_unchecked_mut<U, F>(self: Pin<&'a mut T>, func: F) -> Pin<&'a mut U> where
544 F: FnOnce(&mut T) -> &mut U,
546 let pointer = Pin::get_unchecked_mut(self);
547 let new_pointer = func(pointer);
548 Pin::new_unchecked(new_pointer)
552 #[stable(feature = "pin", since = "1.33.0")]
553 impl<P: Deref> Deref for Pin<P> {
554 type Target = P::Target;
555 fn deref(&self) -> &P::Target {
556 Pin::get_ref(Pin::as_ref(self))
560 #[stable(feature = "pin", since = "1.33.0")]
561 impl<P: DerefMut> DerefMut for Pin<P>
565 fn deref_mut(&mut self) -> &mut P::Target {
566 Pin::get_mut(Pin::as_mut(self))
570 #[unstable(feature = "receiver_trait", issue = "0")]
571 impl<P: Receiver> Receiver for Pin<P> {}
573 #[stable(feature = "pin", since = "1.33.0")]
574 impl<P: fmt::Debug> fmt::Debug for Pin<P> {
575 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
576 fmt::Debug::fmt(&self.pointer, f)
580 #[stable(feature = "pin", since = "1.33.0")]
581 impl<P: fmt::Display> fmt::Display for Pin<P> {
582 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
583 fmt::Display::fmt(&self.pointer, f)
587 #[stable(feature = "pin", since = "1.33.0")]
588 impl<P: fmt::Pointer> fmt::Pointer for Pin<P> {
589 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
590 fmt::Pointer::fmt(&self.pointer, f)
594 // Note: this means that any impl of `CoerceUnsized` that allows coercing from
595 // a type that impls `Deref<Target=impl !Unpin>` to a type that impls
596 // `Deref<Target=Unpin>` is unsound. Any such impl would probably be unsound
597 // for other reasons, though, so we just need to take care not to allow such
598 // impls to land in std.
599 #[stable(feature = "pin", since = "1.33.0")]
600 impl<P, U> CoerceUnsized<Pin<U>> for Pin<P>
605 #[stable(feature = "pin", since = "1.33.0")]
606 impl<'a, P, U> DispatchFromDyn<Pin<U>> for Pin<P>
608 P: DispatchFromDyn<U>,