#[repr(transparent)]
pub struct Cell<T>
where T: ?Sized,
{ value: UnsafeCell<T>, }
Expand description

A mutable memory location.

§Memory layout

Cell<T> has the same memory layout and caveats as UnsafeCell<T>. In particular, this means that Cell<T> has the same in-memory representation as its inner type T.

§Examples

In this example, you can see that Cell<T> enables mutation inside an immutable struct. In other words, it enables “interior mutability”.

use std::cell::Cell;

struct SomeStruct {
    regular_field: u8,
    special_field: Cell<u8>,
}

let my_struct = SomeStruct {
    regular_field: 0,
    special_field: Cell::new(1),
};

let new_value = 100;

// ERROR: `my_struct` is immutable
// my_struct.regular_field = new_value;

// WORKS: although `my_struct` is immutable, `special_field` is a `Cell`,
// which can always be mutated
my_struct.special_field.set(new_value);
assert_eq!(my_struct.special_field.get(), new_value);

See the module-level documentation for more.

Fields§

§value: UnsafeCell<T>

Implementations§

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impl<T> Cell<T>

const: 1.24.0 · source

pub const fn new(value: T) -> Cell<T>

Creates a new Cell containing the given value.

§Examples
use std::cell::Cell;

let c = Cell::new(5);
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pub fn set(&self, val: T)

Sets the contained value.

§Examples
use std::cell::Cell;

let c = Cell::new(5);

c.set(10);
1.17.0 · source

pub fn swap(&self, other: &Cell<T>)

Swaps the values of two Cells. Difference with std::mem::swap is that this function doesn’t require &mut reference.

§Panics

This function will panic if self and other are different Cells that partially overlap. (Using just standard library methods, it is impossible to create such partially overlapping Cells. However, unsafe code is allowed to e.g. create two &Cell<[i32; 2]> that partially overlap.)

§Examples
use std::cell::Cell;

let c1 = Cell::new(5i32);
let c2 = Cell::new(10i32);
c1.swap(&c2);
assert_eq!(10, c1.get());
assert_eq!(5, c2.get());
1.17.0 · source

pub fn replace(&self, val: T) -> T

Replaces the contained value with val, and returns the old contained value.

§Examples
use std::cell::Cell;

let cell = Cell::new(5);
assert_eq!(cell.get(), 5);
assert_eq!(cell.replace(10), 5);
assert_eq!(cell.get(), 10);
1.17.0 (const: unstable) · source

pub fn into_inner(self) -> T

Unwraps the value, consuming the cell.

§Examples
use std::cell::Cell;

let c = Cell::new(5);
let five = c.into_inner();

assert_eq!(five, 5);
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impl<T> Cell<T>
where T: Copy,

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pub fn get(&self) -> T

Returns a copy of the contained value.

§Examples
use std::cell::Cell;

let c = Cell::new(5);

let five = c.get();
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pub fn update<F>(&self, f: F) -> T
where F: FnOnce(T) -> T,

🔬This is a nightly-only experimental API. (cell_update)

Updates the contained value using a function and returns the new value.

§Examples
#![feature(cell_update)]

use std::cell::Cell;

let c = Cell::new(5);
let new = c.update(|x| x + 1);

assert_eq!(new, 6);
assert_eq!(c.get(), 6);
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impl<T> Cell<T>
where T: ?Sized,

1.12.0 (const: 1.32.0) · source

pub const fn as_ptr(&self) -> *mut T

Returns a raw pointer to the underlying data in this cell.

§Examples
use std::cell::Cell;

let c = Cell::new(5);

let ptr = c.as_ptr();
1.11.0 · source

pub fn get_mut(&mut self) -> &mut T

Returns a mutable reference to the underlying data.

This call borrows Cell mutably (at compile-time) which guarantees that we possess the only reference.

However be cautious: this method expects self to be mutable, which is generally not the case when using a Cell. If you require interior mutability by reference, consider using RefCell which provides run-time checked mutable borrows through its borrow_mut method.

§Examples
use std::cell::Cell;

let mut c = Cell::new(5);
*c.get_mut() += 1;

assert_eq!(c.get(), 6);
1.37.0 · source

pub fn from_mut(t: &mut T) -> &Cell<T>

Returns a &Cell<T> from a &mut T

§Examples
use std::cell::Cell;

let slice: &mut [i32] = &mut [1, 2, 3];
let cell_slice: &Cell<[i32]> = Cell::from_mut(slice);
let slice_cell: &[Cell<i32>] = cell_slice.as_slice_of_cells();

assert_eq!(slice_cell.len(), 3);
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impl<T> Cell<T>
where T: Default,

1.17.0 · source

pub fn take(&self) -> T

Takes the value of the cell, leaving Default::default() in its place.

§Examples
use std::cell::Cell;

let c = Cell::new(5);
let five = c.take();

assert_eq!(five, 5);
assert_eq!(c.into_inner(), 0);
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impl<T> Cell<[T]>

1.37.0 · source

pub fn as_slice_of_cells(&self) -> &[Cell<T>]

Returns a &[Cell<T>] from a &Cell<[T]>

§Examples
use std::cell::Cell;

let slice: &mut [i32] = &mut [1, 2, 3];
let cell_slice: &Cell<[i32]> = Cell::from_mut(slice);
let slice_cell: &[Cell<i32>] = cell_slice.as_slice_of_cells();

assert_eq!(slice_cell.len(), 3);
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impl<T, const N: usize> Cell<[T; N]>

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pub fn as_array_of_cells(&self) -> &[Cell<T>; N]

🔬This is a nightly-only experimental API. (as_array_of_cells)

Returns a &[Cell<T>; N] from a &Cell<[T; N]>

§Examples
#![feature(as_array_of_cells)]
use std::cell::Cell;

let mut array: [i32; 3] = [1, 2, 3];
let cell_array: &Cell<[i32; 3]> = Cell::from_mut(&mut array);
let array_cell: &[Cell<i32>; 3] = cell_array.as_array_of_cells();

Trait Implementations§

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impl<T> Clone for Cell<T>
where T: Copy,

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fn clone(&self) -> Cell<T>

Returns a copy of the value. Read more
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fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
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impl<T> Debug for Cell<T>
where T: Copy + Debug,

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fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter. Read more
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impl<T> Default for Cell<T>
where T: Default,

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fn default() -> Cell<T>

Creates a Cell<T>, with the Default value for T.

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impl<'de, T> Deserialize<'de> for Cell<T>
where T: Deserialize<'de> + Copy,

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fn deserialize<D>( deserializer: D ) -> Result<Cell<T>, <D as Deserializer<'de>>::Error>
where D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer. Read more
1.12.0 · source§

impl<T> From<T> for Cell<T>

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fn from(t: T) -> Cell<T>

Creates a new Cell<T> containing the given value.

1.10.0 · source§

impl<T> Ord for Cell<T>
where T: Ord + Copy,

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fn cmp(&self, other: &Cell<T>) -> Ordering

This method returns an Ordering between self and other. Read more
1.21.0 · source§

fn max(self, other: Self) -> Self
where Self: Sized,

Compares and returns the maximum of two values. Read more
1.21.0 · source§

fn min(self, other: Self) -> Self
where Self: Sized,

Compares and returns the minimum of two values. Read more
1.50.0 · source§

fn clamp(self, min: Self, max: Self) -> Self
where Self: Sized + PartialOrd,

Restrict a value to a certain interval. Read more
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impl<T> PartialEq for Cell<T>
where T: PartialEq + Copy,

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fn eq(&self, other: &Cell<T>) -> bool

This method tests for self and other values to be equal, and is used by ==.
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fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.10.0 · source§

impl<T> PartialOrd for Cell<T>
where T: PartialOrd + Copy,

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fn partial_cmp(&self, other: &Cell<T>) -> Option<Ordering>

This method returns an ordering between self and other values if one exists. Read more
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fn lt(&self, other: &Cell<T>) -> bool

This method tests less than (for self and other) and is used by the < operator. Read more
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fn le(&self, other: &Cell<T>) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more
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fn gt(&self, other: &Cell<T>) -> bool

This method tests greater than (for self and other) and is used by the > operator. Read more
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fn ge(&self, other: &Cell<T>) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more
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impl<T> Serialize for Cell<T>
where T: Serialize + Copy,

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fn serialize<S>( &self, serializer: S ) -> Result<<S as Serializer>::Ok, <S as Serializer>::Error>
where S: Serializer,

Serialize this value into the given Serde serializer. Read more
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impl<T, U> CoerceUnsized<Cell<U>> for Cell<T>
where T: CoerceUnsized<U>,

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impl<T, U> DispatchFromDyn<Cell<U>> for Cell<T>
where T: DispatchFromDyn<U>,

1.2.0 · source§

impl<T> Eq for Cell<T>
where T: Eq + Copy,

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impl<T> Send for Cell<T>
where T: Send + ?Sized,

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impl<T> !Sync for Cell<T>
where T: ?Sized,

Auto Trait Implementations§

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impl<T> !RefUnwindSafe for Cell<T>

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impl<T: ?Sized> Unpin for Cell<T>
where T: Unpin,

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impl<T: ?Sized> UnwindSafe for Cell<T>
where T: UnwindSafe,

Blanket Implementations§

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<U> As for U

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fn as_<T>(self) -> T
where T: CastFrom<U>,

Casts self to type T. The semantics of numeric casting with the as operator are followed, so <T as As>::as_::<U> can be used in the same way as T as U for numeric conversions. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T1> DecodeUntypedSlice for T1
where T1: From<UntypedValue>,

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fn decode_untyped_slice(results: &[UntypedValue]) -> Result<T1, UntypedError>

Decodes the slice of [UntypedValue] as a value of type Self. Read more
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impl<T> Downcast for T
where T: Any,

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fn into_any(self: Box<T>) -> Box<dyn Any>

Convert Box<dyn Trait> (where Trait: Downcast) to Box<dyn Any>. Box<dyn Any> can then be further downcast into Box<ConcreteType> where ConcreteType implements Trait.
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fn into_any_rc(self: Rc<T>) -> Rc<dyn Any>

Convert Rc<Trait> (where Trait: Downcast) to Rc<Any>. Rc<Any> can then be further downcast into Rc<ConcreteType> where ConcreteType implements Trait.
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fn as_any(&self) -> &(dyn Any + 'static)

Convert &Trait (where Trait: Downcast) to &Any. This is needed since Rust cannot generate &Any’s vtable from &Trait’s.
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fn as_any_mut(&mut self) -> &mut (dyn Any + 'static)

Convert &mut Trait (where Trait: Downcast) to &Any. This is needed since Rust cannot generate &mut Any’s vtable from &mut Trait’s.
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impl<Q, K> Equivalent<K> for Q
where Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

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fn equivalent(&self, key: &K) -> bool

Compare self to key and return true if they are equal.
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impl<Q, K> Equivalent<K> for Q
where Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

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fn equivalent(&self, key: &K) -> bool

Checks if this value is equivalent to the given key. Read more
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impl<Q, K> Equivalent<K> for Q
where Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

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fn equivalent(&self, key: &K) -> bool

Compare self to key and return true if they are equal.
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impl<T> From<!> for T

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fn from(t: !) -> T

Converts to this type from the input type.
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T> Pointable for T

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const ALIGN: usize = _

The alignment of pointer.
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type Init = T

The type for initializers.
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unsafe fn init(init: <T as Pointable>::Init) -> usize

Initializes a with the given initializer. Read more
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unsafe fn deref<'a>(ptr: usize) -> &'a T

Dereferences the given pointer. Read more
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unsafe fn deref_mut<'a>(ptr: usize) -> &'a mut T

Mutably dereferences the given pointer. Read more
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unsafe fn drop(ptr: usize)

Drops the object pointed to by the given pointer. Read more
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impl<T> Same for T

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type Output = T

Should always be Self
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impl<T> ToOwned for T
where T: Clone,

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type Owned = T

The resulting type after obtaining ownership.
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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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impl<V, T> VZip<V> for T
where V: MultiLane<T>,

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fn vzip(self) -> V

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impl<T> DeserializeOwned for T
where T: for<'de> Deserialize<'de>,