Cell in core::cell - Rust (original) (raw)

Struct Cell

1.6.0 · Source

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

Expand description

A mutable memory location.

§Memory layout

Cell<T> has the same memory layout and caveats asUnsafeCell. In particular, this means thatCell<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.

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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 (const: unstable) · 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 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

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);

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1.0.0 (const: 1.88.0) · Source

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

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);

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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: 1.88.0) · 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: 1.88.0) · 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);

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1.17.0 (const: unstable) · 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);

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1.37.0 (const: 1.88.0) · 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);

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1.91.0 (const: 1.91.0) · Source

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();

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Source

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

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);