Struct std::cell::Cell

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

A mutable memory location.

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);
Run

See the module-level documentation for more.

Fields

value: UnsafeCell<T>

Implementations

Creates a new Cell containing the given value.

Examples
use std::cell::Cell;

let c = Cell::new(5);
Run

Sets the contained value.

Examples
use std::cell::Cell;

let c = Cell::new(5);

c.set(10);
Run

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());
Run

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);
Run

Unwraps the value.

Examples
use std::cell::Cell;

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

assert_eq!(five, 5);
Run

Returns a copy of the contained value.

Examples
use std::cell::Cell;

let c = Cell::new(5);

let five = c.get();
Run
🔬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);
Run

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();
Run

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);
Run

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);
Run

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);
Run

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);
Run
🔬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();
Run

Trait Implementations

Returns a copy of the value. Read more
Performs copy-assignment from source. Read more
Formats the value using the given formatter. Read more

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

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

This method returns an Ordering between self and other. Read more
Compares and returns the maximum of two values. Read more
Compares and returns the minimum of two values. Read more
Restrict a value to a certain interval. Read more
This method tests for self and other values to be equal, and is used by ==. Read more
This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason. Read more
This method returns an ordering between self and other values if one exists. Read more
This method tests less than (for self and other) and is used by the < operator. Read more
This method tests less than or equal to (for self and other) and is used by the <= operator. Read more
This method tests greater than (for self and other) and is used by the > operator. Read more
This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more
Immutably borrows from an owned value. Read more
Mutably borrows from an owned value. Read more
Converts to this type from the input type.

Returns the argument unchanged.

Calls U::from(self).

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

The resulting type after obtaining ownership.
Creates owned data from borrowed data, usually by cloning. Read more
Uses borrowed data to replace owned data, usually by cloning. Read more
The type returned in the event of a conversion error.
Performs the conversion.
The type returned in the event of a conversion error.
Performs the conversion.