Struct tracing_core::stdlib::cell::Cell

1.0.0 · source ·
pub struct Cell<T>where
    T: ?Sized,{
    value: UnsafeCell<T>,
}
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);

See the module-level documentation for more.

Fields§

§value: UnsafeCell<T>

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);
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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);
1.17.0 · source

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.

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 · 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);
1.17.0 (const: unstable) · source

pub fn into_inner(self) -> T

Unwraps the value.

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) -> 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);
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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();
1.11.0 · 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);
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);
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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);
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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);
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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.

1.12.0 (const: unstable) · source§

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

const: unstable · source§

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<Self>,

Restrict a value to a certain interval. Read more
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impl<T> PartialEq<Cell<T>> for Cell<T>where T: PartialEq<T> + 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<Cell<T>> for Cell<T>where T: PartialOrd<T> + 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,

const: unstable · source§

fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for Twhere T: ?Sized,

const: unstable · source§

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

Mutably borrows from an owned value. Read more
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impl<T> From<!> for T

const: unstable · source§

fn from(t: !) -> T

Converts to this type from the input type.
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impl<T> From<T> for T

const: unstable · source§

fn from(t: T) -> T

Returns the argument unchanged.

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

const: unstable · source§

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.
const: unstable · source§

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.
const: unstable · source§

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

Performs the conversion.