# 1.33.0[−][src]Struct std::pin::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 further explanation on pinning.

## Methods

### `impl<P> Pin<P> where
P: Deref,
<P as Deref>::Target: Unpin,` [src]

#### `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.

### `impl<P> Pin<P> where
P: Deref,` [src]

#### `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

#### `pub fn as_ref(&self) -> Pin<&<P as Deref>::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`.

### `impl<P> Pin<P> where
P: DerefMut,` [src]

#### `pub fn as_mut(&mut self) -> Pin<&mut <P as Deref>::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(&mut self, value: <P as Deref>::Target) where
<P as Deref>::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> Pin<&'a T> where
T: ?Sized,` [src]

#### `pub unsafe fn map_unchecked<U, F>(self, 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.

####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'a, R: Read + ?Sized> Read for &'a mut Rimpl<'a, W: Write + ?Sized> Write for &'a mut W`
`pub fn get_ref(self) -> &'a T`[src]

Get 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> Pin<&'a mut T> where
T: ?Sized,` [src]

#### `pub fn into_ref(self) -> Pin<&'a T>`[src]

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

####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'a, R: Read + ?Sized> Read for &'a mut Rimpl<'a, W: Write + ?Sized> Write for &'a mut W`
`pub fn get_mut(self) -> &'a mut T where
T: Unpin,` [src]

Get 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`.

####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'a, R: Read + ?Sized> Read for &'a mut Rimpl<'a, W: Write + ?Sized> Write for &'a mut W`
`pub unsafe fn get_unchecked_mut(self) -> &'a mut T`[src]

Get 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.

#### `pub unsafe fn map_unchecked_mut<U, F>(self, 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> Pointer for Pin<P> where
P: Pointer,` [src]

#### `fn fmt(&self, f: &mut Formatter) -> Result<(), Error>`[src]

Formats the value using the given formatter.

### `impl<P> Display for Pin<P> where
P: Display,` [src]

#### `fn fmt(&self, f: &mut Formatter) -> Result<(), Error>`[src]

Formats the value using the given formatter. Read more

### `impl<P> Copy for Pin<P> where
P: Copy,` [src]

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

### `impl<P> Eq for Pin<P> where
P: Eq,` [src]

### `impl<P> Clone for Pin<P> where
P: Clone,` [src]

#### `fn clone(&self) -> Pin<P>`[src]

Returns a copy of the value. Read more

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

Performs copy-assignment from `source`. Read more

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

### `impl<P> Hash for Pin<P> where
P: Hash,` [src]

#### `fn hash<__HP>(&self, state: &mut __HP) where
__HP: Hasher,` [src]

Feeds this value into the given [`Hasher`]. Read more

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

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

### `impl<P> Debug for Pin<P> where
P: Debug,` [src]

#### `fn fmt(&self, f: &mut Formatter) -> Result<(), Error>`[src]

Formats the value using the given formatter. Read more

### `impl<P> Deref for Pin<P> where
P: Deref,` [src]

#### `type Target = <P as Deref>::Target`

The resulting type after dereferencing.

#### `fn deref(&self) -> &<P as Deref>::Target`[src]

Dereferences the value.

### `impl<P> DerefMut for Pin<P> where
P: DerefMut,
<P as Deref>::Target: Unpin,` [src]

#### `fn deref_mut(&mut self) -> &mut <P as Deref>::Target`[src]

Mutably dereferences the value.

### `impl<P> PartialEq<Pin<P>> for Pin<P> where
P: PartialEq<P>,` [src]

#### `fn eq(&self, other: &Pin<P>) -> bool`[src]

This method tests for `self` and `other` values to be equal, and is used by `==`. Read more

#### `fn ne(&self, other: &Pin<P>) -> bool`[src]

This method tests for `!=`.

### `impl<P> Future for Pin<P> where
P: Unpin + DerefMut,
<P as Deref>::Target: Future,` [src]

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

🔬 This is a nightly-only experimental API. (`futures_api` #50547)

futures in libcore are unstable

The result of the `Future`.

#### `fn poll(
self: Pin<&mut Pin<P>>,
lw: &LocalWaker
) -> Poll<<Pin<P> as Future>::Output>`[src]

🔬 This is a nightly-only experimental API. (`futures_api` #50547)

futures in libcore are unstable

Attempt to resolve the future to a final value, registering the current task for wakeup if the value is not yet available. Read more

### `impl<P> Ord for Pin<P> where
P: Ord,` [src]

#### `fn cmp(&self, other: &Pin<P>) -> Ordering`[src]

This method returns an `Ordering` between `self` and `other`. Read more

#### `fn max(self, other: Self) -> Self`
1.21.0
[src]

Compares and returns the maximum of two values. Read more

#### `fn min(self, other: Self) -> Self`
1.21.0
[src]

Compares and returns the minimum of two values. Read more

### `impl<P> PartialOrd<Pin<P>> for Pin<P> where
P: PartialOrd<P>,` [src]

#### `fn partial_cmp(&self, other: &Pin<P>) -> Option<Ordering>`[src]

This method returns an ordering between `self` and `other` values if one exists. Read more

#### `fn lt(&self, other: &Pin<P>) -> bool`[src]

This method tests less than (for `self` and `other`) and is used by the `<` operator. Read more

#### `fn le(&self, other: &Pin<P>) -> bool`[src]

This method tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more

#### `fn gt(&self, other: &Pin<P>) -> bool`[src]

This method tests greater than (for `self` and `other`) and is used by the `>` operator. Read more

#### `fn ge(&self, other: &Pin<P>) -> bool`[src]

This method tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more

### `impl<T> From<Box<T>> for Pin<Box<T>> where
T: ?Sized,` [src]

#### `fn from(boxed: Box<T>) -> Pin<Box<T>>`[src]

Converts a `Box<T>` into a `Pin<Box<T>>`

This conversion does not allocate on the heap and happens in place.

## Auto Trait Implementations

### `impl<P> Send for Pin<P> where
P: Send,`

### `impl<P> Sync for Pin<P> where
P: Sync,`

## Blanket Implementations

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

#### `fn from(t: T) -> T`[src]

Performs the conversion.

### `impl<T, U> TryFrom for T where
T: From<U>,` [src]

#### `type Error = !`

🔬 This is a nightly-only experimental API. (`try_from` #33417)

The type returned in the event of a conversion error.

#### `fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>`[src]

🔬 This is a nightly-only experimental API. (`try_from` #33417)

Performs the conversion.

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

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

🔬 This is a nightly-only experimental API. (`try_from` #33417)

The type returned in the event of a conversion error.

#### `fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>`[src]

🔬 This is a nightly-only experimental API. (`try_from` #33417)

Performs the conversion.

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

#### `fn into(self) -> U`[src]

Performs the conversion.

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

####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'a, R: Read + ?Sized> Read for &'a mut Rimpl<'a, W: Write + ?Sized> Write for &'a mut W`
`fn borrow(&self) -> &T`[src]

Immutably borrows from an owned value. Read more

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

####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'a, R: Read + ?Sized> Read for &'a mut Rimpl<'a, W: Write + ?Sized> Write for &'a mut W`
`fn borrow_mut(&mut self) -> &mut T`[src]

Mutably borrows from an owned value. Read more

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

#### `fn get_type_id(&self) -> TypeId`[src]

🔬 This is a nightly-only experimental API. (`get_type_id` #27745)

this method will likely be replaced by an associated static

Gets the `TypeId` of `self`. Read more

### `impl<T> ToOwned for T where
T: Clone,` [src]

#### `type Owned = T`

#### `fn to_owned(&self) -> T`[src]

Creates owned data from borrowed data, usually by cloning. Read more

#### `fn clone_into(&self, target: &mut T)`[src]

🔬 This is a nightly-only experimental API. (`toowned_clone_into` #41263)

recently added

Uses borrowed data to replace owned data, usually by cloning. Read more

### `impl<T> ToString for T where
T: Display + ?Sized,` [src]

#### `fn to_string(&self) -> String`[src]

Converts the given value to a `String`. Read more

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