Cell in std::cell - Rust

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>](https://doc.rust-lang.org/std/cell/struct.UnsafeCell.html#memory-layout "struct std::cell::UnsafeCell"). 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.

Source §

1.0.0 (const: 1.24.0) · Source

Creates a new Cell containing the given value.

§ Examples

use std::cell::Cell;

let c = Cell::new(5);

1.0.0 · Source

Sets the contained value.

§ Examples

use std::cell::Cell;

let c = Cell::new(5);

c.set(10);

1.17.0 · Source

Swaps the values of two Cell s.

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 Cell s that partially overlap. (Using just standard library methods, it is impossible to create such partially overlapping Cell s. 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: unstable) · Source

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

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 §

1.0.0 (const: unstable) · Source

Returns a copy of the contained value.

§ Examples

use std::cell::Cell;

let c = Cell::new(5);

let five = c.get();

Source 🔬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);

Source §

1.12.0 (const: 1.32.0) · Source

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: unstable) · Source

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: unstable) · Source

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 §

1.17.0 · Source

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 §

1.37.0 (const: unstable) · Source

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 §

Source 🔬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();

1.0.0 · Source §1.0.0 · Source §1.0.0 · Source §

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

1.12.0 · Source §

Source §

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

1.10.0 · Source §1.0.0 · Source §

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Tests for self and other values to be equal, and is used by ==.

1.0.0 · Source §

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

1.10.0 · Source §