Struct std::cell::Cell

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

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

impl<T> Cell<T>

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);

pub fn set(&self, val: T)

Sets the contained value.

Examples

use std::cell::Cell;

let c = Cell::new(5);

c.set(10);

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.

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());

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);

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);

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

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();

pub fn update<F>(&self, f: F) -> Twhere F: FnOnce(T) -> T,

🔬This is a nightly-only experimental API. (cell_update #50186)

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);

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

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();

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);

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);

impl<T> Cell<T>where T: Default,

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);

impl<T> Cell<[T]>

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);

impl<T, const N: usize> Cell<[T; N]>

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

🔬This is a nightly-only experimental API. (as_array_of_cells #88248)

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

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

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

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

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

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

Formats the value using the given formatter.

impl<T> Default for Cell<T>where T: Default,

fn default() -> Cell<T>

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

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

fn assert_receiver_is_total_eq(&self)

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

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

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

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

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

This method returns an Ordering between self and other.

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

Compares and returns the maximum of two values.

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

Compares and returns the minimum of two values.

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

Restrict a value to a certain interval.

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

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

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

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.

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

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

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

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

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

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.

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

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

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.

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

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

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

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