Struct std::cell::Cell

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

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

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impl<T> Cell<T>

const: 1.24.0source

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);

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pub fn set(&self, val: T)

Sets the contained value.

Examples

use std::cell::Cell;

let c = Cell::new(5);

c.set(10);

1.17.0source

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.

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());

1.17.0source

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);

1.17.0 (const: unstable)source

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);

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

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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();

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pub fn update<F>(&self, f: F) -> T
where
    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);

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

1.12.0 (const: 1.32.0)source

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();

1.11.0source

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);

1.37.0source

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);

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

1.17.0source

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);

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impl<T> Cell<[T]>

1.37.0source

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);

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

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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

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

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

Returns a copy of the value. Read more

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

Performs copy-assignment from source. Read more

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

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

Formats the value using the given formatter. Read more

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

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fn default() -> Cell<T>

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

1.12.0source

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

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

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

1.10.0source

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

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

This method returns an Ordering between self and other. Read more

1.21.0source

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

Compares and returns the maximum of two values. Read more

1.21.0source

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

Compares and returns the minimum of two values. Read more

1.50.0source

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

Restrict a value to a certain interval. Read more

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

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

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

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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.

1.10.0source

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

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

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

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

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

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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. Read more

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

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

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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. Read more

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

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

1.2.0source

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

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

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

Auto Trait Implementations

impl<T> !RefUnwindSafe for Cell<T>

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

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

Blanket Implementations

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impl<T> Any for T
where
    T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more

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impl<T> Borrow<T> for T
where
    T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more

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impl<T> BorrowMut<T> for T
where
    T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more

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impl<T> From<!> for T

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fn from(t: !) -> T

Converts to this type from the input type.

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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where
    U: From<T>,

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fn into(self) -> U

Calls U::from(self).

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

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impl<T> ToOwned for T
where
    T: Clone,

type Owned = T

The resulting type after obtaining ownership.

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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more

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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more

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impl<T, U> TryFrom<U> for T
where
    U: Into<T>,

type Error = Infallible

The type returned in the event of a conversion error.

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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.

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impl<T, U> TryInto<U> for T
where
    U: TryFrom<T>,

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.

© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/cell/struct.Cell.html

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Struct std::cell::Cell

Memory layout

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Trait Implementations

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