1.33.0[][src]Struct core::pin::Pin

#[lang = "pin"]
#[repr(transparent)]
pub struct Pin<P> { /* fields omitted */ }

A pinned pointer.

This is a wrapper around a kind of pointer which makes that pointer "pin" its value in place, preventing the value referenced by that pointer from being moved unless it implements Unpin.

See the pin module documentation for an explanation of pinning.

Methods

impl<P: Deref> Pin<P> where
    P::Target: Unpin
[src]

Important traits for Pin<P>
pub fn new(pointer: P) -> Pin<P>[src]

Construct a new Pin<P> around a pointer to some data of a type that implements Unpin.

Unlike Pin::new_unchecked, this method is safe because the pointer P dereferences to an Unpin type, which cancels the pinning guarantees.

pub fn into_inner(pin: Pin<P>) -> P[src]

🔬 This is a nightly-only experimental API. (pin_into_inner #60245)

Unwraps this Pin<P> returning the underlying pointer.

This requires that the data inside this Pin is Unpin so that we can ignore the pinning invariants when unwrapping it.

impl<P: Deref> Pin<P>[src]

Important traits for Pin<P>
pub unsafe fn new_unchecked(pointer: P) -> Pin<P>[src]

Construct a new Pin<P> around a reference to some data of a type that may or may not implement Unpin.

If pointer dereferences to an Unpin type, Pin::new should be used instead.

Safety

This constructor is unsafe because we cannot guarantee that the data pointed to by pointer is pinned, meaning that the data will not be moved or its storage invalidated until it gets dropped. If the constructed Pin<P> does not guarantee that the data P points to is pinned, that is a violation of the API contract and may lead to undefined behavior in later (safe) operations.

By using this method, you are making a promise about the P::Deref and P::DerefMut implementations, if they exist. Most importantly, they must not move out of their self arguments: Pin::as_mut and Pin::as_ref will call DerefMut::deref_mut and Deref::deref on the pinned pointer and expect these methods to uphold the pinning invariants. Moreover, by calling this method you promise that the reference P dereferences to will not be moved out of again; in particular, it must not be possible to obtain a &mut P::Target and then move out of that reference (using, for example mem::swap).

For example, calling Pin::new_unchecked on an &'a mut T is unsafe because while you are able to pin it for the given lifetime 'a, you have no control over whether it is kept pinned once 'a ends:

use std::mem;
use std::pin::Pin;

fn move_pinned_ref<T>(mut a: T, mut b: T) {
    unsafe {
        let p: Pin<&mut T> = Pin::new_unchecked(&mut a);
        // This should mean the pointee `a` can never move again.
    }
    mem::swap(&mut a, &mut b);
    // The address of `a` changed to `b`'s stack slot, so `a` got moved even
    // though we have previously pinned it! We have violated the pinning API contract.
}Run

A value, once pinned, must remain pinned forever (unless its type implements Unpin).

Similarily, calling Pin::new_unchecked on an Rc<T> is unsafe because there could be aliases to the same data that are not subject to the pinning restrictions:

use std::rc::Rc;
use std::pin::Pin;

fn move_pinned_rc<T>(mut x: Rc<T>) {
    let pinned = unsafe { Pin::new_unchecked(x.clone()) };
    {
        let p: Pin<&T> = pinned.as_ref();
        // This should mean the pointee can never move again.
    }
    drop(pinned);
    let content = Rc::get_mut(&mut x).unwrap();
    // Now, if `x` was the only reference, we have a mutable reference to
    // data that we pinned above, which we could use to move it as we have
    // seen in the previous example. We have violated the pinning API contract.
 }Run

Important traits for Pin<P>
pub fn as_ref(self: &Pin<P>) -> Pin<&P::Target>[src]

Gets a pinned shared reference from this pinned pointer.

This is a generic method to go from &Pin<Pointer<T>> to Pin<&T>. It is safe because, as part of the contract of Pin::new_unchecked, the pointee cannot move after Pin<Pointer<T>> got created. "Malicious" implementations of Pointer::Deref are likewise ruled out by the contract of Pin::new_unchecked.

pub unsafe fn into_inner_unchecked(pin: Pin<P>) -> P[src]

🔬 This is a nightly-only experimental API. (pin_into_inner #60245)

Unwraps this Pin<P> returning the underlying pointer.

Safety

This function is unsafe. You must guarantee that you will continue to treat the pointer P as pinned after you call this function, so that the invariants on the Pin type can be upheld. If the code using the resulting P does not continue to maintain the pinning invariants that is a violation of the API contract and may lead to undefined behavior in later (safe) operations.

If the underlying data is Unpin, Pin::into_inner should be used instead.

impl<P: DerefMut> Pin<P>[src]

Important traits for Pin<P>
pub fn as_mut(self: &mut Pin<P>) -> Pin<&mut P::Target>[src]

Gets a pinned mutable reference from this pinned pointer.

This is a generic method to go from &mut Pin<Pointer<T>> to Pin<&mut T>. It is safe because, as part of the contract of Pin::new_unchecked, the pointee cannot move after Pin<Pointer<T>> got created. "Malicious" implementations of Pointer::DerefMut are likewise ruled out by the contract of Pin::new_unchecked.

pub fn set(self: &mut Pin<P>, value: P::Target) where
    P::Target: Sized
[src]

Assigns a new value to the memory behind the pinned reference.

This overwrites pinned data, but that is okay: its destructor gets run before being overwritten, so no pinning guarantee is violated.

impl<'a, T: ?Sized> Pin<&'a T>[src]

Important traits for Pin<P>
pub unsafe fn map_unchecked<U, F>(self: Pin<&'a T>, func: F) -> Pin<&'a U> where
    F: FnOnce(&T) -> &U, 
[src]

Constructs a new pin by mapping the interior value.

For example, if you wanted to get a Pin of a field of something, you could use this to get access to that field in one line of code. However, there are several gotchas with these "pinning projections"; see the pin module documentation for further details on that topic.

Safety

This function is unsafe. You must guarantee that the data you return will not move so long as the argument value does not move (for example, because it is one of the fields of that value), and also that you do not move out of the argument you receive to the interior function.

pub fn get_ref(self: Pin<&'a T>) -> &'a T[src]

Gets a shared reference out of a pin.

This is safe because it is not possible to move out of a shared reference. It may seem like there is an issue here with interior mutability: in fact, it is possible to move a T out of a &RefCell<T>. However, this is not a problem as long as there does not also exist a Pin<&T> pointing to the same data, and RefCell<T> does not let you create a pinned reference to its contents. See the discussion on "pinning projections" for further details.

Note: Pin also implements Deref to the target, which can be used to access the inner value. However, Deref only provides a reference that lives for as long as the borrow of the Pin, not the lifetime of the Pin itself. This method allows turning the Pin into a reference with the same lifetime as the original Pin.

impl<'a, T: ?Sized> Pin<&'a mut T>[src]

Important traits for Pin<P>
pub fn into_ref(self: Pin<&'a mut T>) -> Pin<&'a T>[src]

Converts this Pin<&mut T> into a Pin<&T> with the same lifetime.

pub fn get_mut(self: Pin<&'a mut T>) -> &'a mut T where
    T: Unpin
[src]

Gets a mutable reference to the data inside of this Pin.

This requires that the data inside this Pin is Unpin.

Note: Pin also implements DerefMut to the data, which can be used to access the inner value. However, DerefMut only provides a reference that lives for as long as the borrow of the Pin, not the lifetime of the Pin itself. This method allows turning the Pin into a reference with the same lifetime as the original Pin.

pub unsafe fn get_unchecked_mut(self: Pin<&'a mut T>) -> &'a mut T[src]

Gets a mutable reference to the data inside of this Pin.

Safety

This function is unsafe. You must guarantee that you will never move the data out of the mutable reference you receive when you call this function, so that the invariants on the Pin type can be upheld.

If the underlying data is Unpin, Pin::get_mut should be used instead.

Important traits for Pin<P>
pub unsafe fn map_unchecked_mut<U, F>(
    self: Pin<&'a mut T>,
    func: F
) -> Pin<&'a mut U> where
    F: FnOnce(&mut T) -> &mut U, 
[src]

Construct a new pin by mapping the interior value.

For example, if you wanted to get a Pin of a field of something, you could use this to get access to that field in one line of code. However, there are several gotchas with these "pinning projections"; see the pin module documentation for further details on that topic.

Safety

This function is unsafe. You must guarantee that the data you return will not move so long as the argument value does not move (for example, because it is one of the fields of that value), and also that you do not move out of the argument you receive to the interior function.

Trait Implementations

impl<P: Copy> Copy for Pin<P>[src]

impl<P: Deref> Deref for Pin<P>[src]

type Target = P::Target

The resulting type after dereferencing.

impl<P: DerefMut> DerefMut for Pin<P> where
    P::Target: Unpin
[src]

impl<'_, G: ?Sized + Generator> Generator for Pin<&'_ mut G>[src]

type Yield = G::Yield

🔬 This is a nightly-only experimental API. (generator_trait #43122)

The type of value this generator yields. Read more

type Return = G::Return

🔬 This is a nightly-only experimental API. (generator_trait #43122)

The type of value this generator returns. Read more

impl<P, U> CoerceUnsized<Pin<U>> for Pin<P> where
    P: CoerceUnsized<U>, 
[src]

impl<'a, P, U> DispatchFromDyn<Pin<U>> for Pin<P> where
    P: DispatchFromDyn<U>, 
[src]

impl<P, Q> PartialEq<Pin<Q>> for Pin<P> where
    P: PartialEq<Q>, 
1.34.0[src]

impl<P: Eq> Eq for Pin<P>[src]

impl<P: Ord> Ord for Pin<P>[src]

fn max(self, other: Self) -> Self where
    Self: Sized
1.21.0[src]

Compares and returns the maximum of two values. Read more

fn min(self, other: Self) -> Self where
    Self: Sized
1.21.0[src]

Compares and returns the minimum of two values. Read more

fn clamp(self, min: Self, max: Self) -> Self where
    Self: Sized
[src]

🔬 This is a nightly-only experimental API. (clamp #44095)

Restrict a value to a certain interval. Read more

impl<P, Q> PartialOrd<Pin<Q>> for Pin<P> where
    P: PartialOrd<Q>, 
1.34.0[src]

impl<P: Clone> Clone for Pin<P>[src]

fn clone_from(&mut self, source: &Self)1.0.0[src]

Performs copy-assignment from source. Read more

impl<P: Hash> Hash for Pin<P>[src]

fn hash_slice<H: Hasher>(data: &[Self], state: &mut H) where
    Self: Sized
1.3.0[src]

Feeds a slice of this type into the given [Hasher]. Read more

impl<P: Debug> Debug for Pin<P>[src]

impl<P: Display> Display for Pin<P>[src]

impl<P: Pointer> Pointer for Pin<P>[src]

impl<P> Future for Pin<P> where
    P: Unpin + DerefMut,
    P::Target: Future
1.36.0[src]

type Output = <<P as Deref>::Target as Future>::Output

The type of value produced on completion.

Auto Trait Implementations

impl<P> Send for Pin<P> where
    P: Send

impl<P> Sync for Pin<P> where
    P: Sync

impl<P> Unpin for Pin<P> where
    P: Unpin

Blanket Implementations

impl<T, U> Into<U> for T where
    U: From<T>, 
[src]

impl<T> From<T> for T[src]

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 
[src]

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 
[src]

type Error = Infallible

The type returned in the event of a conversion error.

impl<T> Borrow<T> for T where
    T: ?Sized
[src]

impl<T> BorrowMut<T> for T where
    T: ?Sized
[src]

impl<T> Any for T where
    T: 'static + ?Sized
[src]