# Struct std::cell::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);

Run

See the module-level documentation for more.

## Implementations§

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### impl<T> Cell<T>

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);

Run
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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);

Run
1.17.0 · source

#### pub fn swap(&self, other: &Cell<T>)

Swaps the values of two `Cell`s. 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 `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());

Run
1.17.0 · source

#### 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);

Run
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);

Run
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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();

Run
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#### pub fn update<F>(&self, f: F) -> Twhere 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);

Run
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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();

Run
1.11.0 · source

#### 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);

Run
1.37.0 · source

#### 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);

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

1.17.0 · source

#### 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);

Run
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### impl<T> Cell<[T]>

1.37.0 · source

#### 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);

Run
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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();

Run

## 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.

1.12.0 · source§

### 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.

1.10.0 · source§

### 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
1.21.0 · source§

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

Compares and returns the maximum of two values. Read more
1.21.0 · source§

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

Compares and returns the minimum of two values. Read more
1.50.0 · source§

#### fn clamp(self, min: Self, max: Self) -> Selfwhere 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.
1.10.0 · source§

### 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>,

1.2.0 · source§

### 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§

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### impl<T> !RefUnwindSafe for Cell<T>

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

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

## Blanket Implementations§

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### impl<T> Any for Twhere 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 Twhere 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 Twhere 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 Twhere 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 Twhere T: Clone,

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#### 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 Twhere U: Into<T>,

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#### 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 Twhere U: TryFrom<T>,

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#### 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.