std::cell

Struct Cell

1.0.0 · Source

pub struct Cell<T>where
    T: ?Sized,
{ /* private fields */ }

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.

Implementations§

Source §

impl<T> Cell<T>

1.0.0 (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);

1.0.0 (const: unstable) · Source

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>)

Available on non-crate feature ferrocene_subset only.

Swaps the values of two Cells.

The difference with std::mem::swap is that this function doesn’t require a &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 (const: 1.88.0) · Source

pub const 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: 1.83.0) · Source

pub const fn into_inner(self) -> T

Available on non-crate feature ferrocene_subset only.

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);

Source §

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

1.0.0 (const: 1.88.0) · Source

pub const 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();

1.88.0 (const: unstable) · Source

pub fn update(&self, f: impl FnOnce(T) -> T)

Available on non-crate feature ferrocene_subset only.

Updates the contained value using a function.

§Examples

use std::cell::Cell;

let c = Cell::new(5);
c.update(|x| x + 1);
assert_eq!(c.get(), 6);

Source §

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

1.12.0 (const: 1.32.0) · Source

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

Available on non-crate feature ferrocene_subset only.

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 (const: 1.88.0) · Source

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

Available on non-crate feature ferrocene_subset only.

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 (const: 1.88.0) · Source

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

Available on non-crate feature ferrocene_subset only.

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);

Source §

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

1.17.0 (const: unstable) · Source

pub fn take(&self) -> T
where T: Default,

Available on non-crate feature ferrocene_subset only.

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);

Source §

impl<T> Cell<[T]>

1.37.0 (const: 1.88.0) · Source

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

Available on non-crate feature ferrocene_subset only.

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);

Source §

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

1.91.0 (const: 1.91.0) · Source

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

Available on non-crate feature ferrocene_subset only.

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

§Examples

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();

Source §

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

Source

pub fn get_cloned(&self) -> Cell<T>

🔬This is a nightly-only experimental API. (cell_get_cloned #145329)

Available on non-crate feature ferrocene_subset only.

Get a clone of the Cell that contains a copy of the original value.

This allows a cheaply Clone-able type like an Rc to be stored in a Cell, exposing the cheaper clone() method.

§Examples

#![feature(cell_get_cloned)]

use core::cell::Cell;
use std::rc::Rc;

let rc = Rc::new(1usize);
let c1 = Cell::new(rc);
let c2 = c1.get_cloned();
assert_eq!(*c2.into_inner(), 1);