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);
See the module-level documentation for more.
Implementations§
source§impl<T> Cell<T>
impl<T> Cell<T>
1.17.0 · sourcepub fn swap(&self, other: &Cell<T>)
pub fn swap(&self, other: &Cell<T>)
Swaps the values of two Cell
s.
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 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());
1.17.0 (const: unstable) · sourcepub fn replace(&self, val: T) -> T
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: 1.83.0) · sourcepub const fn into_inner(self) -> T
pub const 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);
source§impl<T> Cell<T>where
T: Copy,
impl<T> Cell<T>where
T: Copy,
1.0.0 (const: unstable) · sourcepub fn get(&self) -> T
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();
sourcepub fn update<F>(&self, f: F) -> Twhere
F: FnOnce(T) -> T,
🔬This is a nightly-only experimental API. (cell_update
)
pub fn update<F>(&self, f: F) -> Twhere
F: FnOnce(T) -> T,
cell_update
)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);
source§impl<T> Cell<T>where
T: ?Sized,
impl<T> Cell<T>where
T: ?Sized,
1.12.0 (const: 1.32.0) · sourcepub const fn as_ptr(&self) -> *mut T
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 (const: unstable) · sourcepub fn get_mut(&mut self) -> &mut T
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 (const: unstable) · sourcepub fn from_mut(t: &mut T) -> &Cell<T>
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);
source§impl<T> Cell<[T]>
impl<T> Cell<[T]>
1.37.0 (const: unstable) · sourcepub fn as_slice_of_cells(&self) -> &[Cell<T>]
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);
source§impl<T, const N: usize> Cell<[T; N]>
impl<T, const N: usize> Cell<[T; N]>
sourcepub const fn as_array_of_cells(&self) -> &[Cell<T>; N]
🔬This is a nightly-only experimental API. (as_array_of_cells
)
pub const fn as_array_of_cells(&self) -> &[Cell<T>; N]
as_array_of_cells
)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§
1.10.0 · source§impl<T> Ord for Cell<T>
impl<T> Ord for Cell<T>
1.10.0 · source§impl<T> PartialOrd for Cell<T>where
T: PartialOrd + Copy,
impl<T> PartialOrd for Cell<T>where
T: PartialOrd + Copy,
source§impl<T> VirtualAddressSpaceIndependent for Cell<T>where
T: VirtualAddressSpaceIndependent,
impl<T> VirtualAddressSpaceIndependent for Cell<T>where
T: VirtualAddressSpaceIndependent,
impl<T, U> CoerceUnsized<Cell<U>> for Cell<T>where
T: CoerceUnsized<U>,
impl<T, U> DispatchFromDyn<Cell<U>> for Cell<T>where
T: DispatchFromDyn<U>,
impl<T> Eq for Cell<T>
impl<T> PinCoerceUnsized for Cell<T>where
T: ?Sized,
impl<T> Send for Cell<T>
impl<T> !Sync for Cell<T>where
T: ?Sized,
Auto Trait Implementations§
impl<T> !Freeze for Cell<T>
impl<T> !RefUnwindSafe for Cell<T>
impl<T> Unpin for Cell<T>
impl<T> UnwindSafe for Cell<T>where
T: UnwindSafe + ?Sized,
Blanket Implementations§
source§impl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere
T: ?Sized,
source§fn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
source§impl<T> CloneToUninit for Twhere
T: Clone,
impl<T> CloneToUninit for Twhere
T: Clone,
source§unsafe fn clone_to_uninit(&self, dst: *mut T)
unsafe fn clone_to_uninit(&self, dst: *mut T)
clone_to_uninit
)